JP6603116B2 - Photoelectric conversion device - Google Patents

Description

  The present invention relates to a photoelectric conversion device.

  A quantum dot solar cell, known as a new high-efficiency photoelectric conversion device, is an electron that is excited when sunlight of a specific wavelength hits the quantum dot, and when the electron is excited from the valence band to the conduction band. The generated holes are used as carriers.

  In this case, since the photoelectric conversion efficiency of the quantum dot solar cell is related to the total amount of carriers generated in the quantum dot integrated part, for example, the quantum dot integrated part may be thickened to increase the degree of integration of the quantum dots. This will lead to an improvement in power generation.

  Theoretically, carriers in quantum dots are considered to be less susceptible to energy relaxation and disappear.

  However, when a quantum dot integrated part is formed by integrating quantum dots, carriers generated in the quantum dot are likely to disappear by combining with defects existing in the quantum dot integrated part including the barrier layer. There is a problem in that the amount of charge that can reach the electrode is reduced and the photoelectric conversion efficiency cannot be increased.

  In recent years, various structures for improving the current collection performance of carriers in the quantum dot integrated portion have been proposed for such problems. For example, Patent Document 1 shows an example in which a carrier collection unit 105 called a nanorod is arranged in a quantum dot integration unit 103 in which a plurality of quantum dots 101 are integrated as shown in FIG.

JP 2009-536790 Gazette

  However, the carrier collecting unit 105 disclosed so far generally has a so-called columnar body shape such as a cylinder, a column, and a linear structure, and has a horizontal cross section (hereinafter sometimes referred to as a cross section). The shape is isotropic as represented by a circle. For this reason, the above-described conventional carrier collecting unit 105 has a shape in which the surface area per unit volume is not so large. As a result, the conventional carrier collection unit 105 has a problem that the charge collection efficiency is low because the number of quantum dots in contact with the surface is small, and the photoelectric conversion efficiency is still low.

  Therefore, an object of the present invention is to provide a photoelectric conversion device that has high charge collection efficiency and can improve photoelectric conversion efficiency.

The photoelectric conversion device of the present invention is a photoelectric conversion device including a quantum dot layer having a quantum dot integration unit in which a plurality of quantum dots are integrated, and a plurality of carrier collection units provided in the quantum dot integration unit. And the carrier collection part has a columnar part extending in the thickness direction of the quantum dot accumulation part, and the columnar part has a concave part extending in a longitudinal direction of the columnar part on a side surface , the bottom surface of the recess is Ru Tei rounded.
The photoelectric conversion device of the present invention is a photoelectric conversion device including a quantum dot layer having a quantum dot integration unit in which a plurality of quantum dots are integrated, and a plurality of carrier collection units provided in the quantum dot integration unit. The carrier collecting unit includes a base layer for erecting the columnar part, and has a columnar part extending in the thickness direction of the quantum dot integrated part, and the columnar part is formed on the side surface. It has a recess extending in the longitudinal direction of the columnar part.
The photoelectric conversion device of the present invention is a photoelectric conversion device including a quantum dot layer having a quantum dot integration unit in which a plurality of quantum dots are integrated, and a plurality of carrier collection units provided in the quantum dot integration unit. The carrier collecting unit has a columnar part extending in the thickness direction of the quantum dot accumulation part, and the columnar part has a concave part extending in a longitudinal direction of the columnar part on a side surface, The quantum dot integration unit has two groups consisting of an n-type quantum dot group and a p-type quantum dot group. It is arranged in layers.

  According to the present invention, it is possible to obtain a photoelectric conversion device that has high charge collection efficiency and can improve photoelectric conversion efficiency.

It is a disassembled perspective view which shows typically one Embodiment of the photoelectric conversion apparatus of this invention partially. It shows a cross section in the width direction of the columnar part, and is a schematic diagram showing a state where the bottom surface of the recess formed in the columnar part is rounded. It is a perspective view which shows the columnar part whose width | variety by the side of a base layer is wider than the width | variety by the side of an open end. In (a), the quantum dot integrated part is composed of an n-type quantum dot group and a p-type quantum dot group, the n-type quantum dot group is arranged on the columnar part side, and the n-type quantum dot group The cross-sectional schematic diagram which shows the state by which the p-type quantum dot group is arrange | positioned around (a), (b) is the sectional view on the AA line of (a). It is process drawing which shows the manufacturing method of the photoelectric conversion apparatus of this embodiment. (A) is a cross-sectional schematic diagram which shows the conventional photoelectric conversion apparatus, (b) is sectional drawing along the AA of (a).

  FIG. 1 is an exploded perspective view schematically showing a part of an embodiment of the photoelectric conversion device of the present invention. Here, in order to facilitate understanding of the shape of the carrier collection unit, the quantum dot filling amount is reduced. Moreover, although the photoelectric conversion apparatus shown here has shown the quantum dot solar cell with one photoelectric conversion layer 1 as an example, this invention is not limited to this, The photoelectric conversion layer 1 is two or more layers. It also applies to what has become.

  As shown in FIG. 1, in the photoelectric conversion device of this embodiment, a transparent conductive film 3 and a glass substrate 5 are provided in this order on the upper surface side of the photoelectric conversion layer 1, while electrodes are provided on the lower surface side of the photoelectric conversion layer 1. Layer 7 is provided.

  In this photoelectric conversion device, the upper surface side of the glass substrate 5 is the light incident surface 16a, and the lower surface side of the electrode layer 7 is the light emitting surface 16b. In this case, a protective layer, an antireflection material, or the like may be provided on the surface of the glass substrate 11 on the light incident surface 16a side or the surface of the electrode layer 7 on the light emitting surface 16b.

  The photoelectric conversion layer 1 constituting the photoelectric conversion device of the present embodiment has a configuration having a semiconductor substrate 9 and a quantum dot layer 11. In FIG. 1, the semiconductor substrate 9 and between the semiconductor substrate 9 and the carrier collecting unit 15 are illustrated in a simplified manner, but more specifically, the semiconductor substrate 9 is a p / n junction, A bonding layer exists between the semiconductor substrate 9 and the carrier collecting unit 15.

  The quantum dot layer 11 has a structure having a plurality of columnar portions 15A serving as carrier collecting units 15 in a quantum dot integration unit 13 in which a plurality of quantum dots 13a are integrated.

  Here, the columnar portion 15A constituting the carrier collecting portion 15 has a long shape that extends the quantum dot layer 11 in the thickness direction, and one end thereof is a release end 15a. In this case, since one of the columnar portions 15A is the open end 15a, the quantum dots 13a are also present between the open end 15a and the transparent conductive film 3 although not shown in FIG. .

Here, a part of the plurality of columnar portions 15A provided in the quantum dot layer 11 has a concave portion 15U extending in the longitudinal direction of the columnar portion 15A on the side surface 15s of the columnar portion 15A.

  The columnar portion 15A having the concave portion 15U on the side surface 15s has a larger surface area relative to the unit volume as compared with a case where the cross section has an isotropic shape such as a circle. Thereby, even if the volume of the carrier collecting part 15 is the same, the quantum dots 13a accumulated in the quantum dot layer 11 can be brought into contact with the columnar part 15A by the amount corresponding to the large specific surface area. As a result, since the collection efficiency of the carrier C in the columnar part 15A is improved, the open-circuit voltage (Voc) of the photoelectric conversion device is improved, and a quantum dot solar cell having high photoelectric conversion efficiency can be obtained. This is because, when the columnar portion 15A having the recess 15U on the side surface 15s is included in the plurality of columnar portions 15A, the total specific surface area estimated from all the columnar portions 15A existing in the quantum dot layer 11 However, this is because the cross section is larger than the total specific surface area when the cross section is formed by a columnar portion having an isotropic shape.

  From such a point, it is better that the ratio of the columnar portion 15A having the recess 15U on the side surface 15s is larger in the quantum dot layer 11, for example, the columnar portion 15A when the cross section of the quantum dot layer 11 is observed. The ratio of the number to the total number is desirably 50% or more, particularly 90% or more per unit area. Here, if the columnar portion 15A has two or more rows of recesses 15A on the side surface 15s, and the so-called cross section has a gear shape, the contact area between the side surface 15s of the columnar portion 15A and the quantum dots 13a is further increased. The open circuit voltage (Voc) can be further increased.

  In addition, since the columnar portion 15A has a shape in which the concave portion 15U extends along the longitudinal direction as described above, when the quantum dot 13a is placed around the columnar portion 15A, the quantum dot 13a is replaced with the columnar portion. It can arrange | position so that it may densify in the longitudinal direction of 15A, ie, the thickness direction of the quantum dot layer 11. FIG. Thereby, the continuity of the carrier C flowing in the longitudinal direction of the columnar portion 15A is increased, the carrier C is difficult to disappear, and a decrease in current value is suppressed.

  Further, in this photoelectric conversion device, since the photoelectric conversion layer 1 has the semiconductor substrate 9 and the quantum dot layer 11, the band gap of the quantum dot layer 11 is added to the band gap of the semiconductor substrate 9. Therefore, it becomes possible to cover a wide wavelength range.

  FIG. 2 shows a cross section in the width direction of the columnar portion 15A, and is a schematic view showing a state where the bottom surface 15Us of the recess 15U formed in the columnar portion 15A is rounded. The shape of the bottom surface 15Us of the recess 15U does not have to be so sharp as long as the side surface 15s of the columnar portion 15A has the recess 15U. For example, the bottom surface 15Us of the recess 15U is preferably rounded. When the bottom surface 15Us of the recess 15U is rounded, it usually follows the contour shape of the particle-like quantum dots 13a such as a spherical shape or a polygonal shape, and the contact area between the columnar portion 15A and the quantum dots 13a is increased. be able to. Thereby, the collection efficiency of the carrier C can further be improved.

  Further, in this photoelectric conversion device, as shown in FIG. 1, it is desirable that the carrier collecting unit 15 includes a base layer 15B for standing the columnar portion 15A. When the columnar portion 15 </ b> A is provided so as to stand substantially perpendicular to the main surface of the semiconductor substrate 9, the base layer 15 </ b> B having carrier collection capability is provided so as to cover the main surface of the semiconductor substrate 9. And the short circuit by the contact with the quantum dot layer 11 and the transparent conductive film 3 with high carrier density can be prevented. In this case, it is desirable that a concave portion (the concave portion may be a groove shape) is formed on the surface of the base layer 15B so as to match the contour shape of the quantum dots 13a.

FIG. 3 is a perspective view showing a columnar portion whose width on the base layer side is wider than that on the open end side. FIG.
The maximum diameter of the columnar portion 15A when measured in the base layer 15B side to the open end 15a side, when towards the maximum diameter D ₂ of the base layer 15B side is larger than the maximum diameter D ₁ of the open end 15a side Since the columnar portion 15A can increase the current density on the base layer 15B side, the collection efficiency of the carrier C can be further increased.

  In the photoelectric conversion device of the present embodiment, the quantum dot integration unit 13 has two groups of an n-type quantum dot group 13an and a p-type quantum dot group 13ap, and each of the two groups. However, it is desirable that they are arranged in layers from the side close to the carrier collecting unit 15 toward the periphery thereof.

  For example, in FIGS. 4A and 4B, as an example, an n-type quantum dot group 13an is disposed on the columnar portion 15A side, and a p-type quantum dot group 13p is disposed around the n-type quantum dot group 13an. The state of arrangement is shown.

  Normally, the quantum dots 13a receive light energy, so that electrons existing in the quantum dots 13a are excited to the conduction band, and at the same time, holes are formed, which become carriers C and become photoelectric. Conversion happens. At this time, as shown in FIG. 4, in the quantum dot layer 11, a layer constituted by the n-type quantum dot group 13an and a layer constituted by the p-type quantum dot group 13ap are laminated from the columnar portion 15A side. With this configuration, when electrons and holes that can move to the n-type quantum dot group 13an and the p-type quantum dot group 13ap are generated, the electrons and holes are respectively converted into the n-type quantum dot group 13an and p. The type of quantum dot group 13ap becomes easier to move, and thereby the current collecting property of the carrier C can be further improved.

  4A and 4B show a configuration in which the n-type quantum dot group 13an is arranged on the columnar portion 15A side. In this case, the p-type quantum dot group 13ap is arranged on the columnar portion 15A side. Similar photoelectric conversion characteristics can be obtained with the arrangement.

  4A and 4B, the columnar portion 15A is formed directly on the surface of the semiconductor substrate 9, but in this case as well, the columnar portion 15A is similar to the configuration of FIG. A configuration may also be adopted in which the base layer 15B disposed on the semiconductor substrate 9 is formed on the surface.

  Although various semiconductor materials are applied as materials of the quantum dots 13a, the semiconductor substrate 9, the columnar portion 15A, and the base layer 15B constituting the quantum dot integrated portion 13, the energy gap (Eg) is 0. Those having .15 to 4.50 ev are preferred. Specific semiconductor materials include germanium (Ge), silicon (Si), gallium (Ga), indium (In), arsenic (As), antimony (Sb), copper (Cu), iron (Fe), zinc ( It is desirable to use any one selected from Zn), sulfur (S), lead (Pb), tellurium (Te) and selenium (Se), or a compound or oxide thereof.

  In addition, the above-described quantum dots 13a may have a barrier layer (barrier layer) on the surface of the quantum dots 13a because the electron confinement effect can be enhanced. The barrier layer is preferably a material having an energy gap 2 to 15 times that of the semiconductor material to be the quantum dots 13a, and preferably has an energy gap (Eg) of 1.0 to 10.0 ev. In addition, when the quantum dot 13a has a barrier layer on the surface, as a material of the barrier layer, a compound containing at least one element selected from Si, C, Ti, Cu, Ga, S, In and Se ( Semiconductors, carbides, oxides, nitrides) are preferred.

As described above, the photoelectric conversion device according to the present embodiment has been described with reference to FIGS. 1 to 4. 1
When the configuration is such that the band gap of 3a is changed, the wavelength region of light that can be absorbed can be made wider, and a quantum dot solar cell exhibiting higher photoelectric conversion efficiency can be obtained.

  Next, the manufacturing method of the photoelectric conversion apparatus of this embodiment is demonstrated. FIG. 5 is a process diagram showing the method for manufacturing the photoelectric conversion device of this embodiment.

  First, as shown in FIG. 5A, a semiconductor substrate 9 having an electrode layer 7 on one main surface is prepared. Next, as shown in FIG. 5B, a semiconductor film 21 to be the carrier collecting portion 15 is formed on the main surface of the semiconductor substrate 9 opposite to the electrode layer 7, and then on the surface of the semiconductor film 21. A mask 23 is installed. As the mask 23, a mask 23 having a portion other than the columnar portion 15 </ b> A constituting the carrier collecting portion 15 is used.

  Next, as illustrated in FIG. 5C, the columnar portion 15 </ b> A is formed from the semiconductor film 21 by performing an etching process (reactive ion etching (RIE)). At this time, the base layer 15B is formed by leaving the lower layer side of the semiconductor film 21 together with the columnar portion 15A. Here, when the columnar portion 15A has a shape as shown in FIG. 3, a shape obtained by processing the cross section of the mask into a flared shape is used.

  Next, as shown in FIG. 5 (d), the quantum dots 13 a are filled around the carrier collection unit 15 to form the quantum dot layer 11 having the carrier collection unit 15 in the quantum dot accumulation unit 13. Next, after forming the transparent conductive film 3 on the upper surface of the quantum dot layer 1, the glass substrate 5 is placed on the surface of the transparent conductive film 3.

  Next, a protective layer, an antireflection material, or the like is formed on the surface of the glass substrate 5 as necessary.

  Since the photoelectric conversion device obtained as described above includes the columnar portion 15A having the concave portion 15U on the side surface 15s in the quantum dot layer 11, the surface area of the carrier collecting unit 15 (columnar portion 15A) increases, and the carrier C Thus, the collection efficiency can be increased and the photoelectric conversion efficiency can be increased.

  Hereinafter, a photoelectric conversion device provided with one photoelectric conversion layer having the above-described columnar part was produced by the method shown in FIG. 5, and Voc was evaluated. At this time, indium tin oxide (ITO) was used for the transparent conductive film, and gold (Au) was used for the electrode layer. PbS particles (average particle size: 5 nm) were used for the quantum dots. When the photoelectric conversion device shown in FIG. 4 was produced, PbS particles transformed into p-type and n-type were used. Zinc oxide was used for the carrier collection part and the base layer. A silicon substrate was used as the semiconductor substrate.

  The produced photoelectric conversion device has an average thickness of the silicon substrate of 100 μm, an average thickness of the quantum dot integrated film of 1.2 μm, an average thickness of the base layer of 0.05 μm, and an average length in the thickness direction of the carrier collection unit (base layer) From the surface of the substrate to the open end of the carrier collecting part) was 1.0 μm, the average thickness of the electrode layer was 0.1 μm, the average thickness of the transparent conductive film was 0.3 μm, and the average thickness of the glass substrate was 100 μm. .

  Next, the cross section of the produced photoelectric conversion device was observed with a scanning electron microscope, and the shape of the carrier collecting part was confirmed.

  Next, a lead wire was connected between the transparent conductive film and the electrode layer of the obtained photoelectric conversion device, and IV characteristics were measured.

The open circuit voltage (Voc) is the same as the sample No. of the conventional structure. 5 was 0.35 V, whereas sample No. 5 having the structure of FIG. 1 is 0.38 V, and sample No. 1 having the structure of FIG. 2 is 0.40 V, sample No. 2 having the structure of FIG. 3 is 0.39 V and sample No. 3 having the structure of FIG. 4 was 0.42 V, and the sample having a recess extending in the longitudinal direction on the side surface of the columnar part showed a higher open-circuit voltage than the circular cross-sectional sample, and the charge collection efficiency was high. .

1 .... Photoelectric conversion layer 3 .... Transparent conductive film 5 .... Glass substrate 7 ...・ ・ ・ ・ ・ ・ Electrode layer 9 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Semiconductor substrate 11 ・ ・ ・ ・ ・ ・ Quantum dot layer 13 ・ ・ ・ ・ ・ ・ Quantum dot integration Portion 13a... Quantum dot 13an... N-type quantum dot group 13pn... P-type quantum dot group 15. ········································································· Open side 15s (of the carrier collector) ··· Columnar portion 15B ········· Base layer 16a ········ Light incident surface 16b ······· Light exit surface 21 ··· ... Semiconductor film 23 ... ...... mask C ··········· career

Claims (6)

A photoelectric conversion device including a quantum dot layer having a quantum dot integration unit in which a plurality of quantum dots are integrated, and a plurality of carrier collection units provided in the quantum dot integration unit, wherein the carrier collection unit The quantum dot integrated portion has a columnar portion extending in the thickness direction, the columnar portion has a concave portion extending in the longitudinal direction of the columnar portion on the side surface, and the bottom surface of the concave portion is rounded . A photoelectric conversion device characterized by that. The photoelectric conversion device according to claim 1, wherein the carrier collection unit includes a base layer for standing the columnar part. A photoelectric conversion device including a quantum dot layer having a quantum dot integration unit in which a plurality of quantum dots are integrated, and a plurality of carrier collection units provided in the quantum dot integration unit, wherein the carrier collection unit And a base layer for erecting the columnar portion, the columnar portion extending in the thickness direction of the quantum dot integrated portion, and the columnar portion extending on the side surface in the longitudinal direction of the columnar portion. the photoelectric conversion device characterized by having a recess. 4. The photoelectric conversion device according to claim 2 , wherein a width of the columnar portion is wider on the base layer side than on an open end side.   The quantum dot integration unit has two groups consisting of an n-type quantum dot group and a p-type quantum dot group, and each of the two groups is surrounded by a side closer to the carrier collection unit. The photoelectric conversion device according to claim 1, wherein the photoelectric conversion device is arranged in a layered shape toward the surface. A photoelectric conversion device including a quantum dot layer having a quantum dot integration unit in which a plurality of quantum dots are integrated, and a plurality of carrier collection units provided in the quantum dot integration unit, wherein the carrier collection unit The quantum dot integrated part has a columnar part extending in the thickness direction, the columnar part has a concave part extending in the longitudinal direction of the columnar part on the side surface, and the quantum dot integrated part is an n-type 2 and a p-type quantum dot group, and each of the two groups is arranged in layers from the side close to the carrier collecting portion toward the periphery thereof. A photoelectric conversion device characterized by that.