JP2012023400A - Photoelectric conversion element and solid state imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element which can improve an optical absorption rate without thickening a photoelectric conversion layer.SOLUTION: A photoelectric conversion element 100 is provided with a lower electrode 2, an upper electrode 4 opposite to the lower electrode 2 and a photoelectric conversion layer 3 formed between the lower electrode 2 and the upper electrode 4, and the photoelectric conversion element 100 applies bias voltage to between the lower electrode 2 and the upper electrode 4 and picks up photocurrent. In this case, the upper electrode 4 is an electrode on a light entry side, the upper electrode 4 is a transparent electrode, and the lower electrode 2 is a metal electrode having a function of reflecting light.

Description

  The present invention includes a lower electrode, an upper electrode facing the lower electrode, and a photoelectric conversion layer formed between the lower electrode and the upper electrode, and the gap between the lower electrode and the upper electrode. The present invention relates to a photoelectric conversion element that takes out a photocurrent by applying a bias voltage to a solid-state imaging device including the photoelectric conversion element.

  A normal single-plate solid-state imaging device has a disadvantage that light is less likely to be guided to the photodiode due to higher integration of pixels because the photodiode is provided in substantially the same plane as the charge transfer path. Therefore, although incident light is condensed on the photodiode by a microlens or the like, the light collection efficiency is not sufficient, and the light collection efficiency may vary depending on the light incident angle, which causes problems such as shading. . Furthermore, the number of processes increases in forming microlenses, leading to an increase in cost. In order to obtain a color-separated signal, a color filter is also required, which also increases the number of processes and increases costs.

  As an image pickup element having a high aperture ratio, an image pickup element in which a photoelectric conversion element in which an a-Si (amorphous silicon) photoelectric conversion layer is sandwiched between a pair of electrodes is provided on a silicon substrate on which a signal readout circuit is formed has been proposed. (See Patent Document 1). However, with a-Si, it is difficult to separate light in the visible range with good color separation, and a color filter is required, leading to an increase in cost. Further, in order to achieve sufficient light absorption, the thickness of the photoelectric conversion layer needs to be several μm, and the manufacturing cost by the high frequency glow discharge decomposition method is high.

JP-A-8-88341

  The present invention has been made in view of the above circumstances, a photoelectric conversion element capable of improving the light absorption rate without increasing the thickness of the photoelectric conversion layer and sharpening the action spectrum, and the photoelectric conversion element. An object of the present invention is to provide a solid-state imaging device.

  The photoelectric conversion element of the present invention has a lower electrode, an upper electrode facing the lower electrode, and a photoelectric conversion layer including an organic photoelectric conversion material formed between the lower electrode and the upper electrode. A photoelectric conversion element for extracting a photocurrent by applying a bias voltage between the lower electrode and the upper electrode, wherein the upper electrode is a light incident side electrode, and the upper electrode is transparent, The lower electrode is a metal electrode having a light reflection function, the lower electrode is an electrode for extracting electrons, the upper electrode is an electrode for extracting holes, and between the photoelectric conversion layer and the upper electrode A smooth layer made of an organic hole transporting material that relieves unevenness on the surface of the photoelectric conversion layer, the thickness of the photoelectric conversion layer is 50 nm to 100 nm, and the thickness of the smooth layer is 150 nm to 200 nm. There is That.

  In the photoelectric conversion element of the present invention, the organic photoelectric conversion material includes any of materials having a quinacridone skeleton, a phthalocyanine skeleton, and an anthraquinone skeleton.

  The photoelectric conversion element of the present invention includes one in which the hole transporting material is a material having a triphenylamine structure.

  The photoelectric conversion element of the present invention includes one in which the hole transporting material is a material having a starburst amine structure.

  The photoelectric conversion element of the present invention includes an element in which the light absorption rate of the entire photoelectric conversion element with respect to incident light is 80% or more at the absorption peak wavelength of the photoelectric conversion layer.

  The photoelectric conversion element of the present invention includes one having a half-value width of an action spectrum of the photoelectric conversion element with respect to incident light of 130 nm or less.

  The solid-state imaging device according to the present invention includes a plurality of photoelectric conversion elements arranged in an array on the same plane above a semiconductor substrate, and a signal readout for reading a signal corresponding to a signal charge generated in each of the multiple photoelectric conversion elements Part.

  In the solid-state imaging device according to the present invention, the signal reading unit is formed of a CMOS circuit or a CCD formed on the semiconductor substrate.

  According to the present invention, it is possible to provide a photoelectric conversion element capable of improving the light absorption rate without increasing the thickness of the photoelectric conversion layer and sharpening the action spectrum, and a solid-state imaging device including the photoelectric conversion element. it can.

Sectional schematic diagram which shows schematic structure of the photoelectric conversion element for describing 1st embodiment of this invention Sectional schematic diagram which shows schematic structure of the modification of the photoelectric conversion element for describing 1st embodiment of this invention Sectional schematic diagram which shows schematic structure of the modification of the photoelectric conversion element for describing 1st embodiment of this invention Sectional schematic diagram which shows schematic structure of the modification of the photoelectric conversion element for describing 1st embodiment of this invention The figure which shows the result of comparative example simulation The figure which shows the result of simulation 1 The figure which shows the result of simulation 2 The figure which shows the result of simulation 3 The figure which shows the result of simulation 4 The figure which shows the result of simulation 5 The figure which shows the result of simulation 6 Sectional schematic diagram for one pixel of a solid-state imaging device using the photoelectric conversion device described in the first embodiment The figure which shows the arrangement pattern of the pixel of the solid-state image sensor shown in FIG. The figure which shows the result of the comparative example 1 The figure which shows the result of Example 1 The figure which shows the result of Example 1 The figure which shows the result of having actually measured the light absorption rate of the element of Example 1. The figure which shows the result of Example 2

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a photoelectric conversion element for explaining a first embodiment of the present invention.
A photoelectric conversion element 100 shown in FIG. 1 includes a lower electrode 2 formed on a substrate 1, an upper electrode 4 facing the lower electrode 2, and an intermediate layer between the lower electrode 2 and the upper electrode 4. The intermediate layer includes at least the photoelectric conversion layer 3.

  In the example of FIG. 1, light is incident from the upper electrode 4 side, and charges corresponding to the light are generated in the photoelectric conversion layer 3. Then, by applying a bias voltage of 0.1 V to 30 V, for example, to the lower electrode 2 and the upper electrode 4, the charge generated in the photoelectric conversion layer 3 moves to the lower electrode 2 and the upper electrode 4. The signal according to the electric charge moved to either the electrode 2 or the upper electrode 4 can be extracted to the outside.

  The lower electrode 2 is an electrode for collecting charges (electrons or holes) generated in the photoelectric conversion layer 3. As the lower electrode 2, a metal electrode having a reflection function of reflecting light is used. Examples of such metal electrodes include Ag, Al, Ca, In, Mg, Mn, Ta, Ti, V, W, Au, Co, Fe, Mo, Pd, and Pt, or a mixture thereof. The material of the lower electrode 2 may be appropriately selected according to the wavelength of light absorbed by the photoelectric conversion layer 3. For example, when the photoelectric conversion layer 3 absorbs visible light in the range of about 420 nm to about 660 nm, the lower electrode 2 is a metal electrode having a function of reflecting visible light, and the photoelectric conversion layer 3 is in the infrared region. In the case of absorbing light, the lower electrode 2 may be a metal electrode having a function of reflecting infrared light. In addition, since the lower electrode 2 forms the photoelectric conversion layer 3 on it, if this surface is uneven, the photoelectric conversion layer 3 will become the shape reflecting this unevenness, and will lead to the performance deterioration of an element. For this reason, the average surface roughness Ra of the surface of the lower electrode 2 is preferably 3 nm or less.

  The upper electrode 4 is an electrode for collecting charges (electrons or holes) generated in the photoelectric conversion layer 3. Since it is necessary to make light incident on the photoelectric conversion layer 3, the upper electrode 4 is preferably transparent. In this specification, “transparent” means that 80% or more of visible light or infrared light is transmitted. As the transparent electrode material, a transparent conductive oxide is suitable, and ITO (indium oxide doped with Sn) or the like is a candidate from the viewpoint of process suitability and smoothness. Further, the upper electrode 4 may be provided with a function of transmitting light by using a metal thin film deposited with metal. The thickness of the upper electrode 4 varies depending on the material and the required light transmittance, but is preferably in the range of 5 nm to 200 nm.

  The photoelectric conversion layer 3 is composed of a photoelectric conversion material that absorbs light of a specific wavelength and generates a charge corresponding to the absorbed light. The photoelectric conversion layer 3 may have a single layer structure or a multilayer structure. As the photoelectric conversion material constituting the photoelectric conversion layer 3, an inorganic material and an organic material can be used, but it is particularly preferable to use an organic material from the viewpoint of excellent spectral characteristics and sensitivity. From the viewpoint of high photoelectric conversion performance, an organic material having high crystallinity is more preferable. Examples of the organic material constituting the photoelectric conversion layer 3 include materials having a quinacridone skeleton, a phthalocyanine skeleton, and an anthraquinone skeleton. When quinacridone represented by the following chemical formula 1 is used as the photoelectric conversion layer 3, the photoelectric conversion layer 3 can absorb light in the green wavelength region and generate a charge corresponding thereto. In the case where zinc phthalocyanine represented by the following chemical formula 2 is used as the photoelectric conversion layer 3, the photoelectric conversion layer 3 can absorb light in the red wavelength region and generate a charge corresponding thereto. . When anthraquinone A represented by the following chemical formula 3 is used as the photoelectric conversion layer 3, the photoelectric conversion layer 3 can absorb light in the blue wavelength region and generate a charge corresponding thereto. .

  In addition to the photoelectric conversion layer 3, the intermediate layer suppresses injection of charges from the lower electrode 2 and the upper electrode 4 to the photoelectric conversion layer 3 when a bias voltage is applied to the lower electrode 2 and the upper electrode 4. For example, a charge blocking layer may be included.

  In a simple case, when light enters the photoelectric conversion element 100, light in a specific wavelength region of light transmitted through the upper electrode 4 is absorbed by the photoelectric conversion layer 3, and light transmitted through the photoelectric conversion layer 3 is lower The light that is reflected by the electrode 2 and reenters the photoelectric conversion layer 3 and is not absorbed by the photoelectric conversion layer 3 earlier is further absorbed. When a bias voltage is applied to the lower electrode 2 and the upper electrode 4, charges generated in the photoelectric conversion layer 3 are collected by the lower electrode 2 and the upper electrode 4, and a photocurrent is taken out to the outside. Thus, the light absorption rate can be increased by the effect of light reflection at the lower electrode.

  The effect of light reflection can be cited in addition to an increase in absorption rate due to simple light reciprocation. When the photoelectric fields of incident light and reflected light interfere with each other, the light absorption rate changes in a complicated manner depending on the thickness of the intermediate layer, the wavelength of the incident light, and the like. By using this interference effect, the light absorption rate can be further increased.

  Thus, since the light absorption rate of the photoelectric conversion layer 3 is increased by reflecting the light at the lower electrode 2, it is possible to increase the light absorption rate without increasing the thickness of the photoelectric conversion layer 3. Become. As can be seen from a comparison of simulations to be described later, by appropriately designing the film thickness and the material, 80% or more of light can be absorbed at the absorption peak wavelength in the visible region even if the photoelectric conversion layer is made 100 nm or less.

  Furthermore, because of the interference effect, the light absorptance changes according to the thickness of the intermediate layer, the wavelength of incident light, and the like, so the half width of the light absorption spectrum in the photoelectric conversion layer 3 also changes. By utilizing this and designing a material having an appropriate optical constant and its thickness, the absorption spectrum in the photoelectric conversion layer 3 can be sharpened, and the action spectrum of the photoelectric conversion element can be sharpened. Become. As described in Examples 1 and 2 described later, the half width can be set to 130 nm or less.

When the photoelectric conversion layer 3 is thinned, the following problems occur.
Since the transparent conductive oxide used for the upper electrode 4 is generally formed by sputtering, when the upper electrode 4 is formed on the photoelectric conversion layer 3, the photoelectric conversion layer that has already been formed when the upper electrode 4 is formed. The sputtered particles sink into the unevenness of the surface 3 and the device is easily short-circuited. This problem becomes significant when the photoelectric conversion layer 3 is thin. In particular, when a polycrystalline layer formed of a pigment-based material with many irregularities is used as the photoelectric conversion layer, this phenomenon becomes more prominent. Here, the polycrystalline layer is a layer in which microcrystals having the same material and different crystal orientations are gathered, and has a relatively large unevenness on the surface thereof as compared with a single crystal material or an amorphous material.

  Although not directly related to the thinning of the photoelectric conversion layer 3, the upper electrode 4 is formed by a sputtering method. Therefore, the photoelectric conversion layer 3 is easily damaged by plasma at the time of sputtering, and element characteristics are easily deteriorated. Furthermore, as the sputtered particles enter the irregularities on the surface of the photoelectric conversion layer 3, irregularities are also formed on the surface of the upper electrode 4. If the surface of the upper electrode 4 is uneven, a uniform electric field cannot be applied in the photoelectric conversion layer 3 when a bias is applied to the photoelectric conversion layer 3, and a region with a high electric field is generated locally, increasing the leakage current. It becomes the cause of.

Therefore, FIG. 2 shows a configuration for solving such a problem.
FIG. 2 is a schematic cross-sectional view showing a schematic configuration of a modification of the photoelectric conversion element for explaining the first embodiment of the present invention. In FIG. 2, the same components as those in FIG.
The photoelectric conversion element 200 shown in FIG. 2 has a configuration in which a smoothing layer 5 that relaxes unevenness on the surface of the photoelectric conversion layer 3 is added between the photoelectric conversion layer 3 and the upper electrode 4 of the photoelectric conversion element 100 shown in FIG. It is. The average surface roughness Ra of the smooth layer surface is preferably 1 nm or less. In addition, the effect by having introduce | transduced the smooth layer is demonstrated in detail in Japanese Patent Application No. 2006-45955.

  The smooth layer 5 may be any material as long as the surface thereof has little unevenness and does not short-circuit the photoelectric conversion layer 3, and an organic material or an inorganic material can be used. In particular, an amorphous material is preferably used because there is not much unevenness on the surface. The smooth layer 5 is preferably transparent because it is necessary to make light incident on the photoelectric conversion layer 3. The thickness of the smooth layer 5 is preferably in the range of 10 to 300 nm. In particular, 30 nm or more is preferable in order to effectively relieve the unevenness, and if it is too thick, the bias voltage to be applied to the photoelectric conversion layer 3 becomes large, and thus it is preferably 200 nm or less. In order to effectively prevent a short circuit, the average surface roughness Ra of the surface of the smooth layer 5 is preferably 1 nm or less.

  In the photoelectric conversion element 200 shown in FIG. 2, when the upper electrode 4 is an electrode for extracting holes, that is, holes generated in the photoelectric conversion layer 3 are moved to the upper electrode 4 and electrons are moved to the lower electrode 2. When a bias voltage is applied to, the material constituting the smooth layer 5 is preferably a hole transporting material. Examples of the hole transporting material suitable for the smooth layer 5 include a triphenylamine-based organic material having a triphenylamine structure. Further, examples of the triphenylamine organic material include a starburst amine organic material having a starburst amine structure in which the triphenylamine structure is connected in a star shape. Here, the starburst amine structure refers to the structure of TDATA shown in the following chemical formula 4. As the triphenylamine-based organic material, a material represented by the following chemical formula 5 (referred to as amine A) can be used, and as the starburst amine-based organic material, m represented by the following chemical formula 6 is used. -MTDATA (4,4 ', 4' '-tris (3-methylphenylphenylamino) triphenylamine) or the like can be used.

In the photoelectric conversion element 200, when the upper electrode 4 is used as an electrode for extracting electrons, that is, a bias voltage is applied so that electrons generated in the photoelectric conversion layer 3 are moved to the upper electrode 4 and holes are moved to the lower electrode 2. When is applied, the material constituting the smooth layer 5 is preferably an electron transporting material. As an electron transporting material suitable for the smooth layer 5, Alq ₃ (tris (8-hydroxyquinolinato) aluminum (III)) represented by the following chemical formula 7 or a derivative thereof can be used.

  Due to the presence of the smooth layer 5, it is possible to prevent the sputtered particles from entering the irregularities on the surface of the photoelectric conversion layer 3 even when the upper electrode 4 is formed by the sputtering method. Further, the smooth layer 5 can prevent the photoelectric conversion layer 3 from being exposed to plasma. Further, since the upper electrode 4 is formed on the smooth layer 5, the upper electrode 4 can be formed flat, and a uniform electric field can be applied to the photoelectric conversion layer 3. Thus, by providing the smooth layer 5, it becomes possible to prevent the performance deterioration of the photoelectric conversion element 200 at the time of electrode film-forming. In addition, the unevenness | corrugation in the surface of the photoelectric converting layer 3 is notably seen when the photoelectric converting layer 3 is comprised with the polycrystalline layer. For this reason, it is particularly effective to provide the smooth layer 5 in such a configuration. Moreover, you may comprise the smooth layer 5 itself with a photoelectric conversion material. Examples of the organic material constituting the polycrystalline layer include quinacridone described above.

  In the photoelectric conversion element having a structure in which the photoelectric conversion layer shown in FIGS. 1 and 2 is sandwiched between two electrodes, particularly when a transparent electrode having high transparency such as ITO is used as an electrode for extracting electrons, a bias is applied. The dark current is considerably large.

  One possible cause of the dark current is the current flowing from the electrode for extracting electrons into the photoelectric conversion layer when a bias is applied. When a highly transparent electrode such as an ITO transparent electrode is used as an electrode for extracting electrons, holes are injected from the electrode for extracting electrons into the photoelectric conversion layer because the work function of the electrode is relatively large. It was thought that the barrier at the time would be low and hole injection into the photoelectric conversion layer would easily occur. Actually, when examining the work function of a highly transparent metal oxide transparent electrode such as ITO, the work function of the ITO electrode is about 4.8 eV, and the work function of the Al (aluminum) electrode is about 4. It is considerably higher than 3 eV, and other metal oxide-based transparent electrodes other than ITO are about 4. e.g., except for the smallest AZO (Al-doped zinc oxide) of about 4.5 eV. 6 to 5.4 and its work function are known to be relatively large (for example, see J. Vac. Sci. Technol. A17 (4), Jul / Aug 1999 p. 1765-1772, FIG. 1). 12).

  Thus, when the work function of the electrode for extracting electrons is large, the barrier when holes are transferred from the electrode for extracting electrons to the photoelectric conversion layer when a bias is applied is lowered, and photoelectric conversion from the electrode for extracting electrons is performed. It is considered that hole injection tends to occur in the layer, and as a result, dark current increases.

  Therefore, in the photoelectric conversion elements 100 and 200 shown in FIGS. 1 and 2, it is preferable that the work function of the electrode for extracting electrons is 4.5 eV or less. For example, methods for setting the work function of the upper electrode 4 to 4.5 eV or less when the upper electrode 4 is an electrode for extracting electrons are listed below. The adjustment of the work function of the electrode is described in detail in Japanese Patent Application No. 2005-251745.

(A) A work function adjusting layer for adjusting the work function of the upper electrode 2 is provided between the upper electrode 4 and the photoelectric conversion layer 3.
For example, ITO is used as the upper electrode 4 and a metal thin film containing In, Ag, or Mg having a work function of 4.5 eV or less is used as the work function adjusting layer. (B) A conductive transparent metal oxide thin film having a work function of 4.5 eV or less is used as the upper electrode 4.
For example, an AZO thin film having a work function of 4.5 eV is used as the conductive transparent metal oxide thin film. (C) As the upper electrode 4, a transparent electrode doped with metal oxide and having a work function of 4.5 eV or less is used.
For example, an electrode having a work function of 4.5 eV or less by doping Cs into ITO as a conductive metal oxide is used. (D) As the upper electrode 4, an electrode having a work function of 4.5 eV or less by surface-treating a conductive transparent metal oxide thin film is used.
For example, ITO is used as the upper electrode 4, and this ITO is immersed in an alkaline solution and subjected to surface treatment, and an electrode having a work function of 4.5 eV or less is used. Alternatively, an electrode in which ITO is sputtered with Ar ions or Ne ions and surface-treated to have a work function of 4.5 eV or less is used.

  When the lower electrode 2 is an electrode for extracting electrons, the work function of the lower electrode 2 may be 4.5 eV or less. Since the lower electrode 2 originally uses a metal electrode having a small work function, the work function can be easily reduced to 4.5 eV or less by selecting a material.

  When the upper electrode 4 that is an electrode on the light incident side is an electrode for extracting electrons, the work function of the lower electrode 2 that is an electrode for extracting holes is preferably 4.5 eV or more. It has been found that the dark current can be suppressed and the bias voltage can be suppressed low by setting the work function of to 4.5 eV or less.

  As shown in Table 2 below, most of the metals used as the material of the lower electrode 2 have a work function of 4.5 eV or less, and the metals of 4.5 eV or more include Au, Co, Fe, Mo, Pd, Pt etc. or a mixture thereof etc. are mentioned. For this reason, by using these for the lower electrode 2, the work function of the lower electrode 2 can be set to 4.5 eV or more. However, since these do not have a large light reflection function, the light interference effect is weakened. In addition, the material itself is expensive and the manufacturing cost is increased. Therefore, when it is desired to maintain the work function of the lower electrode 2 at 4.5 eV or more while maintaining the optical interference effect and reducing the cost, the configuration shown in FIGS.

  FIG. 3 is a schematic cross-sectional view showing a schematic configuration of a modification of the photoelectric conversion element for explaining the first embodiment of the present invention. 3, the same components as those in FIG. 1 are denoted by the same reference numerals. FIG. 4 is a schematic cross-sectional view showing a schematic configuration of a modification of the photoelectric conversion element for explaining the first embodiment of the present invention. In FIG. 4, the same components as those in FIG.

  In the photoelectric conversion element 300 shown in FIG. 3, a work function adjustment layer 6 for adjusting the work function of the lower electrode 2 is added between the lower electrode 2 and the photoelectric conversion layer 3 of the photoelectric conversion element 100 shown in FIG. This is the configuration. A photoelectric conversion element 400 shown in FIG. 4 has a work function adjustment layer 6 for adjusting the work function of the lower electrode 2 added between the lower electrode 2 and the photoelectric conversion layer 3 of the photoelectric conversion element 200 shown in FIG. This is the configuration. The photoelectric conversion element 300 and the photoelectric conversion element 400 use the upper electrode 4 as an electrode for extracting electrons.

  The work function adjusting layer 6 is for adjusting the work function of the lower electrode 2 to 4.5 eV or more, and a transparent electrode having a work function of 4.5 eV or more is used. As such a transparent electrode material, a transparent conductive oxide is suitable, and ITO (indium oxide doped with Sn) or the like is a candidate from the viewpoint of process suitability and smoothness. Thus, by providing the work function adjustment layer 6, it is possible to relax the restriction on the material selection of the lower electrode 2, while suppressing the dark current while maintaining the light interference effect and reducing the cost. It can be driven with a bias.

  Examples of literature relating to work function adjustment of a transparent electrode made of ITO will be given below.

  Moreover, the metal whose work function is 4.5 or less is enumerated below with the characteristic.

  Hereinafter, specific examples of the intermediate layer including the above-described photoelectric conversion layer 3 will be described.

(Middle layer)
The intermediate layer is formed by stacking or mixing a photoelectric conversion layer, an electron transport site, a hole transport site, an electron blocking site, a hole blocking site, a crystallization preventing site, and the like. Alternatively, the photoelectric conversion layer alone may be used. The photoelectric conversion layer preferably contains an organic p-type compound or an organic n-type compound.

  The organic p-type semiconductor (compound) is a donor-type organic semiconductor (compound), which is mainly represented by a hole-transporting organic compound and refers to an organic compound having a property of easily donating electrons. More specifically, an organic compound having a smaller ionization potential when two organic materials are used in contact with each other. Therefore, any organic compound can be used as the donor organic compound as long as it is an electron-donating organic compound. For example, triarylamine compound, benzidine compound, pyrazoline compound, styrylamine compound, hydrazone compound, triphenylmethane compound, carbazole compound, polysilane compound, thiophene compound, phthalocyanine compound, cyanine compound, merocyanine compound, oxonol compound, polyamine compound, indole Compounds, pyrrole compounds, pyrazole compounds, polyarylene compounds, condensed aromatic carbocyclic compounds (naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, tetracene derivatives, pyrene derivatives, perylene derivatives, fluoranthene derivatives), nitrogen-containing heterocyclic compounds The metal complex etc. which it has as can be used. Not limited to this, as described above, any organic compound having an ionization potential smaller than that of the organic compound used as the n-type (acceptor property) compound may be used as the donor organic semiconductor.

  Organic n-type semiconductors (compounds) are acceptor organic semiconductors (compounds), which are mainly represented by electron-transporting organic compounds and refer to organic compounds that easily accept electrons. More specifically, the organic compound having the higher electron affinity when two organic compounds are used in contact with each other. Therefore, as the acceptor organic compound, any organic compound can be used as long as it is an electron-accepting organic compound. For example, condensed aromatic carbocyclic compounds (naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, tetracene derivatives, pyrene derivatives, perylene derivatives, fluoranthene derivatives), 5- to 7-membered heterocyclic compounds containing nitrogen atoms, oxygen atoms, and sulfur atoms (E.g. pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, quinoxaline, quinazoline, phthalazine, cinnoline, isoquinoline, pteridine, acridine, phenazine, phenanthroline, tetrazole, pyrazole, imidazole, thiazole, oxazole, indazole, benzimidazole, benzotriazole, Benzoxazole, benzothiazole, carbazole, purine, triazolopyridazine, triazolopyrimidine, tetrazaindene, o Metal complexes having as ligands such as saziazole, imidazopyridine, pyralidine, pyrrolopyridine, thiadiazolopyridine, dibenzazepine, tribenzazepine), polyarylene compounds, fluorene compounds, cyclopentadiene compounds, silyl compounds, nitrogen-containing heterocyclic compounds Etc. Note that the present invention is not limited thereto, and as described above, any organic compound having an electron affinity higher than that of the organic compound used as the donor organic compound may be used as the acceptor organic semiconductor.

  Any p-type organic dye or n-type organic dye may be used, but preferably a cyanine dye, styryl dye, hemicyanine dye, merocyanine dye (including zero methine merocyanine (simple merocyanine)), three nucleus Merocyanine dye, 4-nuclear merocyanine dye, rhodacyanine dye, complex cyanine dye, complex merocyanine dye, allopolar dye, oxonol dye, hemioxonol dye, squalium dye, croconium dye, azamethine dye, coumarin dye, arylidene dye, anthraquinone dye, triphenyl Methane dye, azo dye, azomethine dye, spiro compound, metallocene dye, fluorenone dye, fulgide dye, perylene dye, phenazine dye, phenothiazine dye, quinone dye, indigo Dye, diphenylmethane dye, polyene dye, acridine dye, acridinone dye, diphenylamine dye, quinacridone dye, quinophthalone dye, phenoxazine dye, phthaloperylene dye, porphyrin dye, chlorophyll dye, phthalocyanine dye, metal complex dye, condensed aromatic carbocyclic dye (Naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, tetracene derivatives, pyrene derivatives, perylene derivatives, fluoranthene derivatives).

  Next, the metal complex compound will be described. The metal complex compound is a metal complex having a ligand having at least one nitrogen atom or oxygen atom or sulfur atom coordinated to the metal, and the metal ion in the metal complex is not particularly limited, but preferably beryllium ion, magnesium Ion, aluminum ion, gallium ion, zinc ion, indium ion, or tin ion, more preferably beryllium ion, aluminum ion, gallium ion, or zinc ion, and still more preferably aluminum ion or zinc ion. As the ligand contained in the metal complex, there are various known ligands. Examples include the ligands described in “Photochemistry and Photophysics of Coordination Compounds” by Yersin (Springer-Verlag, 1987), “Organic Metal Chemistry-Fundamentals and Applications” (Yukakabo, 1982), etc. .

  The ligand is preferably a nitrogen-containing heterocyclic ligand (preferably having 1 to 30 carbon atoms, more preferably 2 to 20 carbon atoms, particularly preferably 3 to 15 carbon atoms, and a monodentate ligand. Or a bidentate or higher ligand, preferably a bidentate ligand such as a pyridine ligand, a bipyridyl ligand, a quinolinol ligand, a hydroxyphenylazole ligand (hydroxyphenyl) Benzimidazole, hydroxyphenylbenzoxazole ligand, hydroxyphenylimidazole ligand)), alkoxy ligand (preferably 1-30 carbon atoms, more preferably 1-20 carbon atoms, particularly preferably carbon 1-10, for example, methoxy, ethoxy, butoxy, 2-ethylhexyloxy, etc.), aryloxy ligands Preferably it has 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, such as phenyloxy, 1-naphthyloxy, 2-naphthyloxy, 2,4,6-trimethylphenyl Oxy, 4-biphenyloxy, etc.), heteroaryloxy ligands (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as pyridyl. Oxy, pyrazyloxy, pyrimidyloxy, quinolyloxy, etc.), alkylthio ligands (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as methylthio, Ethylthio, etc.), arylthio ligands (preferably having 6 to 30 carbon atoms, more preferred) Has 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, such as phenylthio, etc.), a heterocyclic substituted thio ligand (preferably 1 to 30 carbon atoms, more preferably 1 to carbon atoms). 20, particularly preferably 1 to 12 carbon atoms, such as pyridylthio, 2-benzimidazolylthio, 2-benzoxazolylthio, 2-benzthiazolylthio and the like, or siloxy ligand (preferably Has 1 to 30 carbon atoms, more preferably 3 to 25 carbon atoms, particularly preferably 6 to 20 carbon atoms, and examples thereof include a triphenylsiloxy group, a triethoxysiloxy group, and a triisopropylsiloxy group. More preferably a nitrogen-containing heterocyclic ligand, an aryloxy ligand, a heteroaryloxy group, or a siloxy ligand, Preferably, a nitrogen-containing heterocyclic ligand, an aryloxy ligand, or a siloxy ligand is used.

  The photoelectric conversion layer has a p-type semiconductor layer and an n-type semiconductor layer between a lower electrode and an upper electrode, and at least one of the p-type semiconductor and the n-type semiconductor is an organic semiconductor, and those semiconductors It is preferable that a bulk heterojunction structure layer including the p-type semiconductor and the n-type semiconductor is provided as an intermediate layer between the layers. By including a bulk heterojunction structure, the disadvantage that the carrier diffusion length of the organic layer is short can be compensated, and the photoelectric conversion efficiency can be improved. The bulk heterojunction structure is described in detail in Japanese Patent Application No. 2004-080639.

  The photoelectric conversion layer may contain a structure having two or more repeating structures (tandem structures) of a pn junction layer formed of a p-type semiconductor layer and an n-type semiconductor layer between the lower electrode and the upper electrode. Preferably, more preferably, a thin layer of conductive material is inserted between the repetitive structures. The number of repeating structures (tandem structures) of the pn junction layer may be any number, but is preferably 2 to 50, more preferably 2 to 30, particularly preferably 2 or 10 in order to increase the photoelectric conversion efficiency. It is. Silver or gold is preferable as the conductive material, and silver is most preferable. The tandem structure is described in detail in Japanese Patent Application No. 2004-079930.

  In a photoelectric conversion layer having a p-type semiconductor layer, an n-type semiconductor layer (preferably a mixed / dispersed (bulk heterojunction structure) layer) between the lower electrode and the upper electrode, of the p-type semiconductor and the n-type semiconductor It is also preferable to include an organic compound whose orientation is controlled in at least one direction, and more preferably, it includes a (possible) organic compound whose orientation is controlled in both the p-type semiconductor and the n-type semiconductor. As the organic compound used for the photoelectric conversion site, those having π-conjugated electrons are preferably used, but this π-electron plane is not perpendicular to the substrate (electrode substrate) but is oriented at an angle close to parallel. The more preferable. The angle with respect to the substrate is preferably 0 ° or more and 80 ° or less, more preferably 0 ° or more and 60 ° or less, further preferably 0 ° or more and 40 ° or less, and further preferably 0 ° or more and 20 ° or less. Particularly preferably, it is 0 ° or more and 10 ° or less, and most preferably 0 ° (that is, parallel to the substrate). As described above, the organic compound layer whose orientation is controlled may be partially included in the entire organic layer, but preferably the proportion of the portion whose orientation is controlled with respect to the entire organic layer is 10% or more. More preferably, it is 30% or more, more preferably 50% or more, further preferably 70% or more, particularly preferably 90% or more, and most preferably 100%. Such a state compensates for the shortcoming of the short carrier diffusion length of the organic layer by controlling the orientation of the organic compound in the organic layer in the photoelectric conversion layer, and improves the photoelectric conversion efficiency.

  In the case where the orientation of the organic compound is controlled, it is more preferable that the heterojunction plane (for example, the pn junction plane) is not parallel to the substrate. It is more preferable that the heterojunction plane is oriented not at a parallel to the substrate (electrode substrate) but at an angle close to the vertical. The angle with respect to the substrate is preferably 10 ° or more and 90 ° or less, more preferably 30 ° or more and 90 ° or less, further preferably 50 ° or more and 90 ° or less, and further preferably 70 ° or more and 90 ° or less. Particularly preferably, it is 80 ° or more and 90 ° or less, and most preferably 90 ° (that is, perpendicular to the substrate). The organic compound layer whose heterojunction surface is controlled as described above may be partially included in the entire organic layer. Preferably, the proportion of the portion where the orientation is controlled with respect to the entire organic layer is 10% or more, more preferably 30% or more, more preferably 50% or more, further preferably 70% or more, and particularly preferably 90%. Above, most preferably 100%. In such a case, the area of the heterojunction surface in the organic layer increases, the amount of carriers of electrons, holes, electron-hole pairs, etc. generated at the interface increases, and the photoelectric conversion efficiency can be improved. In the above-described photoelectric conversion film (photoelectric conversion film) in which the orientation of both the heterojunction plane and the π-electron plane of the organic compound is controlled, the photoelectric conversion efficiency can be particularly improved. These states are described in detail in Japanese Patent Application No. 2004-079931. In terms of light absorption, the thickness of the organic dye layer is preferably as large as possible, but considering the ratio that does not contribute to charge separation, the thickness of the organic dye layer is preferably 30 nm to 300 nm, more preferably 50 nm to 250 nm, Especially preferably, it is 80 nm or more and 200 nm or less.

(Formation method of organic layer)
The layer containing these organic compounds is formed by a dry film formation method or a wet film formation method. Specific examples of the dry film forming method include a physical vapor deposition method such as a vacuum evaporation method, a sputtering method, an ion plating method, a molecular beam epitaxy method, or a chemical vapor deposition method such as plasma polymerization. As the wet film forming method, a coating method, a spin coating method, a dipping method, an LB method, or the like is used.
In the case where a polymer compound is used as at least one of a p-type semiconductor (compound) or an n-type semiconductor (compound), it is preferable to form a film by a wet film formation method that is easy to create. When a dry film formation method such as vapor deposition is used, it is difficult to use a polymer because it may be decomposed, and the oligomer can be preferably used instead. On the other hand, when a low molecule is used, a dry film forming method is preferably used, and a vacuum deposition method is particularly preferably used. The vacuum deposition method is basically based on the method of heating compounds such as resistance heating deposition method and electron beam heating deposition method, shape of deposition source such as crucible and boat, degree of vacuum, deposition temperature, base temperature, deposition rate, etc. It is a parameter. In order to enable uniform deposition, it is preferable to perform deposition by rotating the substrate. The higher the degree of vacuum is, preferably 10 ⁻² Pa or less, preferably 10 ⁻⁴ Pa or less, particularly preferably 10 ⁻⁶ Pa or less. It is preferable that all steps during the vapor deposition be performed in the above-described vacuum, and basically the compound is not directly in contact with oxygen and moisture in the outside air. The above-described conditions of vacuum deposition affect the crystallinity, amorphousness, density, density, etc. of the organic film, and must be strictly controlled. It is preferable to use PI or PID control of the deposition rate using a film thickness monitor such as a quartz crystal resonator or an interferometer. When two or more kinds of compounds are vapor-deposited simultaneously, a co-evaporation method, a flash vapor deposition method, or the like can be preferably used.

(electrode)
The transparent electrode is preferably made plasma-free. By creating a transparent electrode without plasma, the influence of plasma on the substrate can be reduced, and the photoelectric conversion characteristics can be improved. Here, plasma free means that no plasma is generated during the formation of the transparent electrode, or the distance from the plasma generation source to the substrate is 2 cm or more, preferably 10 cm or more, more preferably 20 cm or more, and reaches the substrate. It means a state where the plasma to be reduced decreases.

  Examples of apparatuses that do not generate plasma during the formation of the transparent electrode include an electron beam heating vapor deposition apparatus (EB vapor deposition apparatus) and a pulse laser vapor deposition apparatus. Regarding the EB deposition system or pulse laser deposition system, the supervision of Yutaka Sawada “New development of transparent conductive film” (CMC, 1999), the supervision of Yutaka Sawada “New development of transparent conductive film II” (CMC, 2002), Devices as described in “Transparent conductive film technology” by the Japan Society for the Promotion of Science (Ohm Co., 1999) and references attached to them can be used. Hereinafter, a method of forming a transparent electrode film using an EB vapor deposition apparatus is referred to as an EB vapor deposition method, and a method of forming a transparent electrode film using a pulse laser vapor deposition apparatus is referred to as a pulse laser vapor deposition method. For an apparatus that can realize a state in which the distance from the plasma generation source to the substrate is 2 cm or more and the arrival of plasma to the substrate is reduced (hereinafter referred to as a plasma-free film forming apparatus), for example, an opposed target sputtering Equipment, arc plasma deposition, etc. are considered, and these are supervised by Yutaka Sawada “New development of transparent conductive film” (CMC, 1999), and supervised by Yutaka Sawada “New development of transparent conductive film II” (CMC, 2002). ), “Transparent conductive film technology” (Ohm Co., 1999) by the Japan Society for the Promotion of Science, and references and the like appended thereto can be used.

Next, the effect obtained by providing the lower electrode 2 with a light reflecting function will be described based on simulation results.
In this simulation, the material of the photoelectric conversion layer 3 was quinacridone (hereinafter abbreviated as QA), which is a pigment-based organic material. The light absorptance simulation calculation based on the light interference calculation was performed according to the method of Document 1 or 2 below. Here, QA, m-MTDATA, and Alq ₃ which are materials used in this simulation are described in J. Org. A. The Ψ spectrum and Δ spectrum were measured using a W-Llam V-VASE rotational analyzer ellipsometer, and optical constants (refractive index n and extinction coefficient k) were determined. These various materials are vapor-deposited on a quartz substrate under the same conditions as those for producing a photoelectric conversion element, and reflected light is measured at an incident angle of 50, 60, and 70 ° with respect to light in a wavelength range of 350 nm to 1100 nm, The transmitted light was measured at an incident angle of 0 °. Other materials used for this simulation, ITO, Al, Ag, and Au, were calculated by interpolating literature values.

Reference 1: L. A. A. Pettersson et al. , Journal of Applied Physics, 86, 487 (1999).
Reference 2: P.M. Peumans et al. , Journal of Applied Physics, 93, 3693 (2003).

(Comparison simulation)
In the photoelectric conversion element 100 having the configuration shown in FIG. 1, the lower electrode 2 and the upper electrode 4 are each ITO, the thickness of the lower electrode 2 is 100 nm, the thickness of the upper electrode 4 is 10 nm, and the thickness of the photoelectric conversion layer 3 is 20 nm. , 50 nm, 100 nm, and 150 nm, the light absorptance in the whole photoelectric conversion element 100 and the light absorptance in the photoelectric conversion layer 3 were calculated. The result is shown in FIG. FIG. 5A is a diagram showing the relationship between the light absorption rate of the entire photoelectric conversion element and the wavelength of incident light (absorption spectrum of the entire element), and FIG. 5B shows the light in the photoelectric conversion layer. It is a figure which shows the relationship (absorption spectrum of only a photoelectric converting layer) of an absorptance and the wavelength of incident light. In FIG. 5A, the light absorbed by materials other than QA is also added, and the value is larger than that of (b). The light irradiation was calculated assuming that the irradiation was performed from above the upper electrode 4. In the comparative simulation element, the thickness of the QA needs to be 150 nm in order to make the light absorption rate at the absorption peak wavelength that is the wavelength most absorbed by QA (G wavelength range) 80% or more. I understand.

(Simulation 1)
In the comparative simulation element, the light absorption rate was calculated by changing the lower electrode 2 to Al. The result is shown in FIG. FIG. 6A is a diagram illustrating the relationship between the light absorption rate of the entire photoelectric conversion element and the wavelength of incident light, and FIG. 6B is the light absorption rate of the photoelectric conversion layer and the wavelength of incident light. It is a figure which shows the relationship.

(Simulation 2)
In the element of simulation 1, the thickness of the photoelectric conversion layer 3 is fixed to 50 nm, m-MTDATA is added as a smoothing layer between the photoelectric conversion layer 3 and the upper electrode 4, and the thickness of the smoothing layer is set to 0 nm, 100 nm, The light absorptance was calculated by changing the thickness to 125 nm, 150 nm, and 175 nm. The result is shown in FIG. FIG. 7A is a diagram showing the relationship between the light absorption rate of the entire photoelectric conversion element and the wavelength of incident light, and FIG. 7B is the light absorption rate of the photoelectric conversion layer and the wavelength of incident light. It is a figure which shows the relationship.

(Simulation 3)
In the comparative simulation element, the light absorption rate was calculated by changing the lower electrode 2 to Ag. The result is shown in FIG. FIG. 8A is a diagram illustrating the relationship between the light absorption rate of the entire photoelectric conversion element and the wavelength of incident light, and FIG. 8B is the light absorption rate of the photoelectric conversion layer and the wavelength of incident light. It is a figure which shows the relationship.

(Simulation 4)
In the element of simulation 3, the thickness of the photoelectric conversion layer 3 is fixed to 50 nm, m-MTDATA is added as a smooth layer between the photoelectric conversion layer 3 and the upper electrode 4, and the thickness of the smooth layer is 0 nm, 100 nm, The light absorptance was calculated by changing the thickness to 125 nm, 150 nm, and 175 nm. The result is shown in FIG. FIG. 9A is a diagram showing the relationship between the light absorption rate of the entire photoelectric conversion element and the wavelength of incident light, and FIG. 9B is the light absorption rate of the photoelectric conversion layer and the wavelength of incident light. It is a figure which shows the relationship.

(Simulation 5)
In the comparative simulation element, the light absorption rate was calculated by changing the lower electrode 2 to Au. The result is shown in FIG. FIG. 10A is a diagram showing the relationship between the light absorption rate of the entire photoelectric conversion element and the wavelength of incident light, and FIG. 10B is the light absorption rate of the photoelectric conversion layer and the wavelength of incident light. It is a figure which shows the relationship.

(Simulation 6)
In the element of the simulation 5, the thickness of the photoelectric conversion layer 3 is fixed to 50 nm, Alq ₃ is added as a smooth layer between the photoelectric conversion layer 3 and the upper electrode 4, and the thickness of the smooth layer is 0 nm, 20 nm, 50 nm. The optical absorptance was calculated by changing to 70 nm. The result is shown in FIG. FIG. 11A is a diagram showing the relationship between the light absorption rate of the entire photoelectric conversion element and the wavelength of incident light, and FIG. 11B shows the light absorption rate of the photoelectric conversion layer and the wavelength of incident light. It is a figure which shows the relationship.

  As can be seen from FIG. 5, when the lower electrode 2 is made transparent, the thickness of the QA needs to be about 150 nm in order to make the light absorption at the QA absorption peak wavelength about 80%. However, if the thickness of the QA is increased to 150 nm or more, the carrier transportability of the QA is small (particularly the electron transportability is small), so that the electrons generated by light absorption cannot be sufficiently moved to the electrode, As a result, the external quantum efficiency is impaired.

  On the other hand, as shown in FIGS. 6 to 11, according to the elements of simulations 1 to 6, even if the thickness of QA is reduced, the light absorption rate can be increased as compared with the element of the simulation for comparison. 6 to 9, it can be seen that even when the thickness of the QA is 50 nm, the Q light can absorb about 90% of the G light. With this thin layer thickness, the low electron transport property of the QA layer can be covered to some extent. Similarly, it can be seen from the results of FIGS. 10 and 11 that even when the QA thickness is 50 nm, the GA can absorb about 70% of the G light.

  Further, considering the magnitude of the light absorption rate and the spectrum waveform, and considering that a certain level of the thickness of the smooth layer is necessary from the viewpoint of preventing a short circuit, the results of FIG. 7 and FIG. A thickness of about 150 nm can be judged to be appropriate because of the high G light absorption rate. In this case, the light absorptance of G light in QA was about 90%.

(Second embodiment)
In the present embodiment, a solid-state imaging device using the photoelectric conversion elements 100 to 400 described in the first embodiment will be described.
FIG. 12 is a schematic cross-sectional view of one pixel of the solid-state imaging device using the photoelectric conversion element described in the first embodiment. The solid-state imaging device 500 has a large number of one pixel shown in FIG. 12 arranged in an array on the same plane, and can generate one pixel data of image data by a signal obtained from the one pixel. .

  One pixel of the solid-state imaging device 500 shown in FIG. 12 is provided with one photoelectric conversion device described in any of FIGS. 1 to 4 above a semiconductor substrate such as silicon, and charges generated by the photoelectric conversion device are converted into semiconductors. Reading is performed by a signal reading unit formed on the substrate. In FIG. 12, only the lower electrode, the photoelectric conversion layer, and the upper electrode are illustrated as photoelectric conversion elements provided above the semiconductor substrate for the sake of simplicity.

  One pixel of the solid-state imaging device 500 is formed on the p-type silicon substrate 10, the p-type silicon substrate 10, the lower electrode 15, the photoelectric conversion layer 16 formed on the lower electrode 15, and the photoelectric conversion layer 16. The photoelectric conversion element including the upper electrode 17 is formed with the lower electrode 15 facing the p-type silicon substrate 10 side. The lower electrode 15 corresponds to the lower electrode 2 in FIGS. 1 to 4, the photoelectric conversion layer 16 corresponds to the photoelectric conversion layer 3 in FIGS. 1 to 4, and the upper electrode 17 corresponds to the upper portion in FIGS. 1 to 4. It corresponds to the electrode 4. The lower electrode 15 is divided for each pixel. The upper electrode 17 may be divided for each pixel, or may be shared by all pixels.

  An n-type high concentration impurity region (n + region) 11 is formed in the p-type silicon substrate 10. The p-type silicon substrate 10 is formed with a signal reading unit (not shown) composed of a CCD, a CMOS circuit, or the like that reads a signal corresponding to the electric charge accumulated in the n + region 11. On the n + region 11, a connection portion 14 made of metal or the like for electrically connecting the n + region 11 and the lower electrode 15 is formed. An insulating layer 13 is formed between the silicon substrate 10 and the lower electrode 15, and a light shielding film 12 for preventing light from entering the connection portion 14 and the signal readout portion is formed in the insulating layer 13. ing. If the insulating layer 13 is opaque, the light shielding film 12 may be omitted. A transparent insulating layer 18 is formed on the upper electrode 17.

  The large number of pixels constituting the solid-state imaging device 500 includes three types of pixels: an R pixel for detecting R light, a G pixel for detecting G light, and a B pixel for detecting B light. Is included. The photoelectric conversion layer 16 included in the R pixel is made of a material that absorbs R light and generates a charge corresponding thereto. The photoelectric conversion layer 16 included in the G pixel is made of a material that absorbs G light and generates a charge corresponding thereto. The photoelectric conversion layer 16 included in the B pixel is made of a material that absorbs B light and generates a charge corresponding thereto.

  These three types of pixels are arranged in a predetermined arrangement pattern. As this arrangement pattern, for example, a Bayer-like arrangement as shown in FIG. 13A or a stripe-like arrangement as shown in FIG. 13B can be adopted. A square shown in FIG. 13 represents a pixel, and a symbol in the square represents a color detected by the pixel.

  Here, the solid-state image sensor 500 is assumed to be composed of three types of pixels. However, the number of types of pixels may be two or more. Also, the type of pixel is not limited to the above-described primary color light detection pixel, and may be a pixel that detects complementary color light.

  When an organic material is used as the photoelectric conversion layer 16 of each pixel of the solid-state imaging device 500 as shown in FIG. 12, it is necessary to devise its manufacturing method. Organic materials are vulnerable to heat, moisture, and the like, and if the photoelectric conversion layer 16 is formed by a photolithography method in the same manner as a color filter of a single-plate solid-state imaging device, the performance of the photoelectric conversion layer 16 deteriorates. Because. Therefore, it is effective to form the photoelectric conversion layer 16 by evaporating the material constituting the photoelectric conversion layer 16 at a predetermined position on the already formed lower electrode 15 through a mask such as a metal mask.

  For example, after forming the lower electrode 15, first, a photoelectric conversion material that absorbs R light is deposited through a metal mask r in which an opening is formed at a position where the photoelectric conversion layer 16 that absorbs R light is to be formed. Next, a photoelectric conversion material that absorbs G light is deposited through a metal mask g in which an opening is formed at a position where the photoelectric conversion layer 16 that absorbs G light is to be formed. Finally, a photoelectric conversion material that absorbs B light is vapor-deposited through a metal mask b in which an opening is formed at a position where the photoelectric conversion layer 16 that absorbs B light is to be formed, and R light, G light, B The photoelectric conversion layer 16 that absorbs light may be formed on the same plane. By doing in this way, the photoelectric converting layer 16 can be formed, without using a photolithography method.

  Thus, when forming the photoelectric conversion layer 16 through a mask, if the arrangement pattern is as shown in FIG. 13B, the metal masks r, g, and b are used as the same mask, and the mask is used in the horizontal direction. Since a large number of photoelectric conversion layers 16 can be formed by simply shifting one-dimensionally and depositing different materials, the manufacturing becomes easier as compared with the arrangement pattern shown in FIG.

  Note that when the optimum smoothing layer has the same thickness for each photoelectric conversion layer that absorbs R light, G light, and B light, the smoothing layer can be formed at a time without using a mask. In this case, the manufacturing becomes easy, and the unevenness between the photoelectric conversion layers can be alleviated, so that problems such as pixel short-circuiting or increase in leakage current can be reduced.

  Next, what kind of effect can be obtained by providing the lower electrode 2 with a light reflecting function will be described based on the result of actually creating a photoelectric conversion element and conducting an experiment.

(Comparative Example 1)
An ITO film having a thickness of 100 nm was formed on the substrate, and In2 nm was deposited thereon to form a lower electrode having a work function of 4.5 eV or less. A quinacridone (QA) film having a thickness of 100 nm is formed thereon to form a photoelectric conversion layer, a m-MTDATA film having a thickness of 100 nm is formed thereon to form a smooth layer, and an ITO film having a thickness of 10 nm is formed thereon. To form a photoelectric conversion element. FIG. 14 shows an action spectrum which is a relationship between the wavelength of incident light and the external quantum efficiency when the photoelectric conversion element is irradiated with light having a wavelength of 550 nm and an intensity of 50 μW / cm ² from the upper electrode. As shown in FIG. 14, when a bias voltage of 2 V is applied to the upper electrode and the lower electrode, an external quantum efficiency of about 6% is obtained at the QA absorption peak wavelength.

Example 1
On the substrate, Al is formed to a thickness of 100 nm to form a lower electrode, quinacridone (QA) is deposited to a thickness of 50 nm to form a photoelectric conversion layer, and m-MTDATA is deposited to a thickness of 150 nm on the smooth surface. A layer was formed, and a 10-nm thick ITO film was formed thereon to form an upper electrode, thereby producing a photoelectric conversion element. The average surface roughness Ra of the surface of m-MTDATA after m-MTDATA film formation is about 0.8 nm. FIG. 15 shows an action spectrum that is a relationship between the wavelength of incident light and the external quantum efficiency when the photoelectric conversion element is irradiated with light having a wavelength of 550 nm and an intensity of 50 μW / cm ² from the upper electrode. Further, FIG. 16 shows the relationship between the average electric field strength applied to the intermediate layer of the photoelectric conversion element and the photocurrent and dark current.

Since the thickness of the intermediate layer and the element of Comparative Example 1 are the same, the external quantum efficiency is compared with the same bias voltage. In the device of Example 1, it can be seen that the external quantum efficiency when 2 V is applied is as high as about 10% even though the thickness of QA is as thin as 50 nm. When the bias voltage is increased, the external quantum efficiency is further increased. For example, when 16 V is applied, the dark current is 3 nA / cm ² and the external quantum efficiency is 42%. In addition, the half-value width of the action spectrum of the element of Comparative Example 1 is about 150 nm, but the half-value width of the action spectrum of the element of Example 1 is about 120 nm, and the half-value width is reduced due to the effect of optical interference. I understand.

  FIG. 17 shows the results of actual measurement of the light absorptance of the device of Example 1. Measurement was performed by collecting the reflected light with a spectrophotometer equipped with an integrating sphere. Although the value of the long wave region derived from the plasmon absorption of Al is deviated, it can be seen that the other regions substantially coincide with the calculation results shown in FIG. This is probably due to inaccurate literature values for the constants). This also confirms that the light absorptance at the absorption peak wavelength of this element has reached 90% or more by providing the lower electrode with a reflecting function. Therefore, it can be considered that the improvement in external quantum efficiency despite the thin photoelectric conversion layer is due to the effect that the light absorptance is increased by providing the lower electrode with a reflection function. In addition, when the photoelectric conversion layer is thin, the effect of increasing the collection efficiency of carriers (particularly electrons) generated by light absorption is also included.

(Example 2)
A film of m-MTDATA in Example 1 was formed with a film thickness of 175 nm, and a photoelectric conversion element exactly the same as in Example 1 was prepared. The average surface roughness Ra of the surface of m-MTDATA after m-MTDATA film formation is about 0.8 nm. FIG. 18 shows an action spectrum that is a relationship between the wavelength of incident light and the external quantum efficiency when the photoelectric conversion element is irradiated with light having a wavelength of 550 nm and an intensity of 50 μW / cm ² from the upper electrode.

  In the device of Example 2, the peak value of the external quantum efficiency at the same bias was slightly smaller than that of the device of Example 1, which is considered to be because the film thickness was slightly increased. It should be noted that the half-value width of the action spectrum has become very small and sharpened. The full width at half maximum is as small as about 90 nm.

  The above result can be predicted from the calculation result of the simulation 2 shown in FIG. It can be seen that when the film thickness is 175 nm, the absorption at the photoelectric conversion film is very slightly reduced, but the half-value width is very small, compared with the case where the m-MTDATA film thickness is 150 nm. Thus, the half width can be changed by utilizing the effect of optical interference. It shows that the half width of the action spectrum can be reduced by appropriately designing the film thickness of m-MTDATA. The technique for controlling the half-value width is considered to be particularly important for an image sensor in which spectral sensitivity characteristics are important.

  Hereinafter, an example demonstrates the dark current suppression effect obtained by setting the work function of the electrode for extracting electrons described in the above embodiment to 4.5 eV or less.

(Comparative Example 2)
A glass substrate (commercially available) on which an ITO electrode having a thickness of 250 nm (a work function of 4.8 eV obtained with an atmospheric photoelectron spectrometer AC-2 manufactured by Riken Keiki Co., Ltd .; visible light transmittance of about 90%) was laminated A structure in which a quinacridone having a thickness of 100 nm and an Al electrode having a thickness of 100 nm (work function 4.3 eV; visible light transmittance 0%) are sequentially stacked by vacuum deposition. Take the case of collecting electrons on the side as an example. As a result of actual device fabrication and measurement with an element area of 2 mm × 2 mm, the dark current was as large as 9.3 μA / cm ² when a voltage of 1 V was applied. In this case, since the work function of ITO, which is an electrode for extracting electrons, is large, when a bias voltage is applied, holes are likely to be injected from the ITO electrode to quinacridone, and the dark current is considered to increase.

(Example 3)
A device similar to Comparative Example 2 was fabricated except that In having a small work function of 4.3 eV was laminated on the ITO electrode by 2 nm vacuum vapor deposition, and In was interposed between the quinacridone and the ITO electrode (2 nm In Of visible light transmittance of about 98%). As a result, the dark current when a voltage of 1 V was applied was greatly suppressed by 1.8 nA / cm ² and about 4 digits. This indicates that hole injection from the electrode for extracting electrons is greatly suppressed by reducing the work function of the ITO electrode, which is an electrode for extracting electrons. Similarly, when 550 nm light was incident from the ITO electrode side at an irradiation intensity of 50 μW / cm ² under the 1 V bias application condition, the external quantum efficiency (measured charge number relative to the number of incident photons) was 12%. When a bias voltage of 2 V was applied, the dark current was about 100 nA / cm ² and the external quantum efficiency was 19%.

Example 4
In the element of Example 3, the Al electrode is replaced with an ITO electrode (work function 4.8 eV; visible region light transmittance 98%) to adjust the work function of the hole extraction electrode. The device was fabricated. Here, the ITO transparent electrode formed in place of the Al electrode was formed on the organic film with a thickness of 10 nm at 40 W by RF magnetron sputtering. At the time of ITO sputtering film formation, some elements were short-circuited due to damage to the organic film due to plasma, but measurements were performed on elements that could be formed without short-circuiting. When light was incident under the same conditions as in Example 3 under a 2 V bias application condition, the dark current was 40 nA / cm ² and the external quantum efficiency was 42%.

Even when compared with Example 3, a further reduction of the dark current (bias 2V applied ^{upon: 100nA / cm 2 ⇒40nA / cm} 2) was confirmed. In addition, as a result of irradiating light under the same conditions as in Example 3, it was confirmed that the external quantum efficiency was improved (when bias 2 V was applied: 19% to 42%).

  The bias voltage for applying a certain electric field strength inside the intermediate layer varies depending on the combination of electrodes sandwiching the intermediate layer. For example, in the element of Example 4 in which the work function of the electrode for extracting electrons is 4.3 eV and the work function of the electrode for extracting holes is 4.8 eV, the work function of the electrode for extracting electrons is 4.8 eV. The work function of the device of Comparative Example 2 in which the work function of the hole extracting electrode is 4.3 eV and the work function of the electron extracting electrode is 4.3 eV, and the work function of the hole extracting electrode is 4. Compared with the element of Example 3 having 3 eV, the same electric field strength can be applied to the intermediate layer with a low bias. This can be expected to reduce the bias. In fact, the device of Example 4 has an external quantum efficiency of 19% at a bias of 1.5 V, and has the same external quantum efficiency at a lower bias than the device of Example 3. As described above, when the electrode on the light incident side is an electrode for extracting electrons, the work function of the electrode for extracting electrons is 4.5 eV or less, and the work function of the electrode for extracting holes is 4.5 eV or more. Thus, it was found that the bias voltage can be suppressed together with the dark current.

1 Substrate 2 Lower electrode 3 Photoelectric conversion layer 4 Upper electrode 5 Smooth layer 6 Work function adjustment layer

Claims (8)

A lower electrode; an upper electrode facing the lower electrode; and a photoelectric conversion layer including an organic photoelectric conversion material formed between the lower electrode and the upper electrode. The lower electrode and the upper electrode A photoelectric conversion element that extracts a photocurrent by applying a bias voltage between
The upper electrode is a light incident side electrode;
The upper electrode is transparent;
The lower electrode is a metal electrode having a light reflecting function;
The lower electrode is an electrode for extracting electrons, and the upper electrode is an electrode for extracting holes,
Between the photoelectric conversion layer and the upper electrode, comprising a smooth layer made of an organic hole transporting material that relaxes irregularities on the surface of the photoelectric conversion layer,
The photoelectric conversion layer has a thickness of 50 nm to 100 nm,
The photoelectric conversion element whose thickness of the said smooth layer is 150 nm-200 nm. The photoelectric conversion element according to claim 1,
The photoelectric conversion element in which the organic photoelectric conversion material contains any one of materials of a quinacridone skeleton, a phthalocyanine skeleton, and an anthraquinone skeleton. The photoelectric conversion element according to claim 1, wherein
A photoelectric conversion element, wherein the hole transporting material is a material having a triphenylamine structure. The photoelectric conversion element according to claim 3,
A photoelectric conversion element, wherein the hole transporting material is a material having a starburst amine structure. It is a photoelectric conversion element in any one of Claims 1-4, Comprising:
The photoelectric conversion element whose light absorption factor of the said whole photoelectric conversion element with respect to incident light is 80% or more in the absorption peak wavelength of the said photoelectric conversion layer. It is a photoelectric conversion element in any one of Claims 1-5, Comprising:
The photoelectric conversion element whose half width of the action spectrum of the said photoelectric conversion element with respect to incident light is 130 nm or less. The photoelectric conversion element according to any one of claims 1 to 6, wherein a large number of the photoelectric conversion elements are arranged in an array on the same plane above the semiconductor substrate,
A solid-state imaging device comprising: a signal reading unit that reads a signal corresponding to a signal charge generated in each of the plurality of photoelectric conversion elements. The solid-state imaging device according to claim 7,
A solid-state imaging device, wherein the signal readout unit is a CMOS circuit or a CCD formed on the semiconductor substrate.

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