JP2004363580A - Photoelectric conversion device and photovoltaic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly efficient photoelectric conversion device such as a multilayer thin film solar cell and a photovoltaic power generation device which can ensure high reliability.
SOLUTION: A plurality of photoelectric conversion units each having a photoactive layer are provided as a laminate, and a photoactive layer of at least one of the photoelectric conversion units is provided with a TO mode scattering peak obtained by a Raman scattering spectrum. The photoelectric conversion device is constituted by an amorphous silicon semiconductor thin film having a ratio of the scattering peak intensity of the TA mode to the intensity of 0.35 or less. This makes it possible to provide a highly efficient photoelectric conversion device such as a multilayer thin-film solar cell and the like and a photovoltaic device using the same, which can ensure high reliability.
[Selection diagram] Fig. 1

Description

  The present invention relates to a multilayer thin-film photoelectric conversion device in which a plurality of photoelectric conversion units each having a photoactive layer are stacked, and in particular, an amorphous Si semiconductor containing at least silicon (Si) and hydrogen (H) as a photoactive layer. The present invention relates to a photoelectric conversion device using a thin film and a photovoltaic device using the photoelectric conversion device as a power generation unit.

  Devices using amorphous Si-based films typified by hydrogenated amorphous silicon (hereinafter also referred to as a-Si: H) are very diversified today. Solar cells have been particularly attracting attention as public interest has increased.

  The feature of amorphous Si in a solar cell is that the light absorption coefficient is much larger than that of crystalline Si (including microcrystalline Si). When the film is formed by a CVD method (chemical vapor deposition method) such as PECVD method (plasma CVD method), the productivity is much higher than when crystalline Si is used. It is to be excellent. However, on the other hand, it has long been known that amorphous silicon has a photodegradation phenomenon generally called the Staebler-Wronski effect, and a solar cell using this film has an efficiency of about 10 to 15% by light irradiation. The problem of declining continues to this day.

Although the mechanism of the photodegradation phenomenon has not yet been clarified, it is argued that it is a phenomenon related to hydrogen, and several approaches have been tried so far. That is, [1] reducing the Si—H ₂ (die hydride) bonding state in the film (increase the ratio of the Si—H (monohydride) bonding state), [2] reducing the hydrogen concentration in the film, [3] For example, fine crystal grains are appropriately contained in the film. However, [1] and [2] have overlapping portions.

The above [1] is based on the fact that a film having a high Si—H ₂ density in the film has a large photodegradation. Research on a specific method of reducing the density of Si—H ₂ in a film has been carried out by many organizations under various hypotheses. For example, the origin of the Si—H ₂ bond state in the film is described as follows. , considered to be in the high-order silane molecules in the gas phase is sterically hindered disturbing the film growth reaction by incorporated into the film, or film-forming surface, SiH ₂ involved in reaction for producing the high-order silane molecules Some attempt to reduce the production of molecules. Specifically, in the PECVD method, plasma having a low electron temperature such as VHF plasma is used, the hydrogen dilution rate is optimized (minimizing the electron temperature), and the substrate temperature is raised to some extent (the upper limit is 350). Attempts have been made to accelerate the hydrogen elimination reaction from the film-forming surface. Under the conditions of a film-forming speed of 2 nm / sec, a-Si having a stabilization efficiency of 8.2% and a light deterioration rate of 12%: H single element characteristics are obtained (see Non-Patent Document 1). However, the efficiency and the light degradation rate are not yet sufficient.

  Regarding the above [2], for example, in the film formation by the PECVD method, a method of extracting excess hydrogen from the surface layer of the film growth while alternately repeating film deposition and hydrogen plasma treatment has been proposed (Patent Document 1). 1, 2, 3). However, in this method, the hydrogen concentration in the film is not sufficiently reduced as expected, and it is difficult to obtain a high film formation rate because the film deposition and the hydrogen plasma treatment are repeated many times. The problem is that the productivity is very poor. Moreover, high efficiency and a low light degradation rate have not been achieved at the same time.

  The above [3], which uses an amorphous Si film which is said to be obtained near the phase boundary region between amorphous Si and microcrystalline Si, has recently attracted attention. This film has not yet been given a fixed name, and is called “Protocrystalline Si: H (Protocrystalline Si)” (see Non-Patent Document 2) or “Nanocrystal embedded amorphous Si (amorphous Si)” depending on the research period. (Non-Patent Document 3) or "Nanostructure-controlling Si film (Crystalline Si nanoclusters well-dispersed in amorphous Si)" (See Non-Patent Documents 4 and 5), but the common concept is "Nano which has an amorphous film characteristic but has a significantly reduced (or almost no) light degradation. Amorphous Si film containing crystal grains of a size. "

  In addition, when it is desired to particularly designate a film including the nano-sized crystal grains among the amorphous Si films, the film is referred to as a “nano crystal grain-containing amorphous Si film” in this specification. I do.

By the way, there are at least two reasons why the amorphous Si film containing nanocrystal grains exhibits a very small light deterioration rate (or hardly any light deterioration). That is, (1) since the recombination of carriers occurs preferentially in the crystal grains due to the scattered distribution of nano-sized crystal grains in the film, the recombination in the amorphous region is reduced (a-Si: H film) Is considered that the photo-deterioration of light is caused by the breakage of the weak Si-Si bond in the amorphous network by the energy released at the time of carrier recombination.) (2) Nano-sized crystal grains are formed in the film. This is because the network structure of the amorphous Si film is hardly deteriorated by light due to the scattered distribution (due to relaxation of strain, etc.), but in any case, it is present in the film. It is thought that nano-sized grains play an important role.
JP-A-5-166733 JP-A-6-120152 JP 2002-9317 A Applied Physics Vol.71 No.7 (2002) p.823 Twenty Ace I Triple E Photovoltaic Specialists Conference (28th-IEEE Photovoltaic Specialists Conference) 2000, p. 750 Proceedings of the 63rd Autumnal Society of Applied Physics (2002) p.838 (25p-ZM-3) Proceedings of the 63rd Autumn Meeting of the Japan Society of Applied Physics (2002) p.27 (25p-B-4) Proceedings of the 63rd Autumn Meeting of the Japan Society of Applied Physics (2002) p.845 (24p-ZM-9)

  However, even in a solar cell using an amorphous Si film containing nanocrystal grains, although the photodegradation rate is certainly reduced, there is still a problem that the initial efficiency is low (for example, Non-Patent Document 1). In Reference 3, the initial efficiency is 6.28% and the stabilization efficiency is 6.03%).

  Therefore, the present invention has been made in view of such a problem, and an object of the present invention is to provide a highly efficient photoelectric conversion device such as a multilayer thin-film solar cell capable of ensuring high reliability and a photovoltaic device using the same as a power generation means. It is to provide a device.

In order to achieve the above-mentioned object, a photoelectric conversion device of the present invention includes: 1) a plurality of photoelectric conversion units each having a photoactive layer as a laminate, and at least one photoelectric conversion unit among the plurality of photoelectric conversion units. of the photoactive layer, the ratio of the scattering peak intensity _{I TA} of TA (horizontal acoustic vibration) mode for scattering peak intensity _{I tO} of tO (horizontal optical vibration) mode obtained by Raman scattering spectrum _(I TA _/ I _tO) 0.35 It is characterized by comprising the following amorphous silicon semiconductor thin film.

Also, 2) a plurality of photoelectric conversion units having a photoactive layer are provided as a laminate, and the photoactive layer of at least one of the plurality of photoelectric conversion units is a TO mode of a TO mode obtained from a Raman scattering spectrum. It is characterized by comprising an amorphous silicon semiconductor thin film having a half width of a scattering peak of 65 cm ^-1 or less.

  3) The configuration according to 1) or 2) above, wherein in two of the plurality of photoelectric conversion units, the photoactive layer of one of the photoelectric conversion units located on the light incident side (front surface side) Is larger than the optical band gap of the photoactive layer of the other photoelectric conversion unit located on the back side of the photoelectric conversion unit.

Here, particularly, 4) in the photoelectric conversion device according to any one of the above 1) to 3), the photoactive layers of at least two photoelectric conversion units are provided with the scattering peak intensities I _TO and TA of the TO mode obtained from the Raman scattering spectrum. An amorphous silicon semiconductor thin film having a mode scattering peak intensity I _TA ratio (= I _TA / I _TO ) of 0.35 or less may be used.

5) In the photoelectric conversion device according to any one of the above 1) to 3), the photoactive layer of at least two photoelectric conversion units may have a half-width of a TO mode scattering peak obtained from a Raman scattering spectrum of 65 cm ^-1. It may be composed of the following amorphous silicon semiconductor thin film.

6) In the photoelectric conversion device according to any one of the above 1) to 3), the photoactive layers of all the photoelectric conversion units are provided with a TO mode scattering peak intensity I _TO obtained from a Raman scattering spectrum and a TA mode scattering. It may be made of an amorphous silicon semiconductor thin film having a peak intensity _ITA ratio ( _ITA / _ITO ) of 0.35 or less.

7) In the photoelectric conversion device according to any one of the above 1) to 3), the photoactive layers of all the photoelectric conversion units have a TO mode scattering peak half width of 65 cm ⁻¹ or less obtained from a Raman scattering spectrum. And an amorphous silicon semiconductor thin film.

  8) In the photoelectric conversion device according to any one of 1) to 5) above, the photoactive layer of the photoelectric conversion unit located on the light incident side is formed of the amorphous silicon semiconductor thin film, and The photoactive layer of the located photoelectric conversion unit may be composed of a microcrystalline silicon-based thin film.

  9) In the photoelectric conversion device according to any one of 1) to 5) above, the photoactive layer of the photoelectric conversion unit located on the light incident side is formed of the amorphous silicon semiconductor thin film, and the photoelectric conversion layer on the back side is formed. The conversion unit may be constituted by a photoelectric conversion unit using a semiconductor substrate.

  10) In the photoelectric conversion device according to any one of 1) to 9), a transparent intermediate layer may be disposed between the at least two photoelectric conversion units.

  11) In the photoelectric conversion device of the above 10), in the photoelectric conversion device of the above 10) which is in contact with the transparent intermediate layer and the transparent intermediate layer, the photoelectric conversion device has a first electrode, at least two It may have a structure in which a photoelectric conversion unit and a second electrode are sequentially formed, and an interface between the substrate and the first electrode may have an uneven shape.

  13) In the photoelectric conversion device according to 10), the photoelectric conversion device has a structure in which a first electrode, at least two photoelectric conversion units, and a second electrode are sequentially formed on a substrate, The interface between the first electrode and the photoelectric conversion unit may have an uneven shape.

  14) In the photoelectric conversion device according to 10), the photoelectric conversion device has a structure in which a first electrode, at least two photoelectric conversion units, and a second electrode are sequentially formed on a substrate, The interface between the photoelectric conversion unit and the second electrode may have an uneven shape.

  15) In the photoelectric conversion device according to 10), the photoelectric conversion device has a structure in which a first electrode, at least two photoelectric conversion units, and a second electrode are sequentially formed on a substrate, A transparent conductive film may be interposed between the photoelectric conversion unit and the second electrode, and an interface between the second transparent conductive film and the second electrode may have an uneven shape.

  16) In the photoelectric conversion device according to any one of the above 12) to 15), the substrate may also serve as the first electrode.

Further, 17) in the photoelectric conversion device of the above 16), wherein the amorphous type silicon semiconductor thin film is the ratio of the scattering peak intensity I _TO and TA mode scattering peak intensity I _TA of TO mode obtained by Raman scattering spectrum (I _TA / I _TO ) may be 0.25 or less.

18) In the photoelectric conversion device described in 16) above, the initial ESR spin density before light stabilization in the amorphous silicon semiconductor thin film may be 5 × 10 ¹⁵ / cm ³ or less.

19) In the photoelectric conversion device as described in 16) above, the existence density in the Si—H bonding state and the Si—H ₂ (Si—H (monohydride) bonding state) in the amorphous silicon semiconductor thin film. The ratio of the existence density of the (die hydride) bonded state to the total density may be 0.95 or more.

  20) In the photoelectric conversion device according to 16) above, the amount of hydrogen in the amorphous silicon semiconductor thin film may be 7 atom% or less.

  21) In the photoelectric conversion device according to 16), a plurality of crystal grains are present in the amorphous silicon semiconductor thin film, and the volume fraction (crystallization rate) occupied by the crystal grains is 30%. The following may be adopted.

  22) In the photoelectric conversion device as described in 16) above, in the amorphous silicon semiconductor thin film, a plurality of crystal grains are scattered and distributed in the thin film, and the maximum grain size of the crystal grains is 1 nm to 5 nm. The following may be adopted.

  Further, the photovoltaic device of the present invention is characterized in that the photovoltaic device of the present invention is configured to use any one of the photoelectric conversion devices of the above 1) to 22) as a power generating means, and to supply the power generated by the power generating means to a load. And

The photoelectric conversion device of the present invention includes a plurality of photoelectric conversion units each having a photoactive layer as a laminate, and the photoactive layer of at least one of the photoelectric conversion units is formed by a TO that can be obtained by Raman scattering spectrum. The ratio of the scattering peak intensity I _TA of the TA mode to the scattering peak intensity I _TO of the mode is made of an amorphous silicon semiconductor thin film in which the ratio I _TA / I _TO is 0.35 or less. In addition, since a photoactive layer having a low defect density and high light stability can be obtained, a highly efficient photoelectric conversion device such as a multi-layer thin-film solar cell that can ensure high reliability can be provided.

In addition, the photoelectric conversion device of the present invention includes a plurality of photoelectric conversion units each having a photoactive layer as a laminate, and obtains a photoactive layer of at least one of the photoelectric conversion units from a Raman scattering spectrum. Since the half-width of the scattering peak of the TO mode to be obtained is made of an amorphous silicon semiconductor thin film having a half value width of 65 cm ^-1 or less, the SRO has been greatly improved as compared with the related art, and a low defect density and high light stability have been obtained. Since a photoactive layer can be used, a highly efficient photoelectric conversion device such as a multilayer thin-film solar cell that can ensure high reliability can be provided.

  Further, according to the photovoltaic device of the present invention, the photoelectric conversion device of the present invention is used as power generating means, and the power generated by the power generating means is supplied to the load, thereby providing a high-efficiency photovoltaic device. can do.

  Hereinafter, embodiments of a photoelectric conversion device of the present invention and a photovoltaic device using the same will be described in detail.

  In order to obtain the amorphous Si film of the present invention, a Cat-PECVD method (a cathodic plasma CVD method with a built-in thermal catalyst; Japanese Patent Application No. 2001-313272, Japanese Patent Application No. 2001-293031, etc.) (See Reference Example). Note that the amorphous Si film here means a film having a crystallization rate defined by a Raman scattering spectrum falling within a range of 0 to 60% as defined later (that is, amorphous Si film). The film is included in the amorphous Si film), whereas the crystalline Si film means a film having a crystallization ratio in the range of 60 to 100%.

<Cat-PECVD method>
When the Cat-PECVD method is used, the amorphous Si film of the present invention uses a VHF band (27 MHz or more: usually about 40 to 80 MHz) as a plasma excitation frequency and uses Ta (tantalum) provided inside the cathode. , W 1400 to 2000 ° C. the temperature of the thermal catalyst consisting of a refractory material such as (tungsten) or C (carbon), 2-20 gas flow ratio _{(H 2 / SiH 4),} 100~350 ℃ substrate temperature And a gas pressure of 13 to 665 Pa and a VHF plasma power density of 0.01 to 0.5 W / cm ² . Here, until H ₂ and SiH ₄ are released into the film forming space, they are led in different states through different gas introduction paths, and the H ₂ gas introduction path is part of the paths. The thermal catalyst provided in the cathode is disposed, but the thermal catalyst is not disposed in the SiH ₄ gas introduction path. By activating only H ₂ by heating with the thermal catalyst in this manner, film deposition / consumption in the gas introduction path until SiH ₄ is decomposed and activated by the thermal catalyst and released into the film forming space. The effect of using a thermal catalyst, which will be described later, can be obtained while preventing such a phenomenon.

By a gas heating effects due to the use of thermal catalyst in the cat-PECVD method, the high-order silane formation reaction is exothermic (SiH ₂ insertion reaction to _Si n _{H m} molecules) is suppressed, a film The density of the higher order silane molecules in the space can be kept low, and the incorporation of the higher order silane molecules into the film and the occurrence of steric hindrance on the film formation surface are reduced. As a result, it becomes possible to form an amorphous Si film in which the existence density of the Si—H ₂ bond state in the film is greatly reduced.

In addition, since the gas heating effect also has the effect of lowering the electron temperature of the plasma, the generation of SiH ₂ by the one-electron collision reaction between the source gas SiH ₄ and the electrons in the plasma space (similarly, the generation of SiH ₃ by the one-electron collision reaction). is compared require high electron temperature (collision energy) by) is suppressed, whereby it is possible to suppress the high-order silane formation reaction (SiH ₂ insertion reaction to Si _n H _m molecules) also.

  In addition, since the Cat-PECVD method can promote the generation of hydrogen radicals, the hydrogen abstraction reaction from the film formation surface can be promoted, and the hydrogen concentration in the film can be effectively reduced.

Further, under film forming conditions in which the hydrogen dilution ratio (gas flow ratio H ₂ / SiH ₄ ) is increased, the temperature of the thermal catalyst Tcat is increased, or the VHF power is increased, Si clusters (higher order silanes) The growth of molecules to some extent usually refers to a size of up to about 10 nm, which includes those having an amorphous structure and those having a crystal structure. Due to the heating effect and the hydrogen radical generation promoting effect, it is possible to control the cluster size and density, and further promote the crystallization of the cluster, while suppressing the growth into particles and powder. That is, when the Si clusters are taken into the film, a high-quality nanocrystalline-particle-containing amorphous Si film in which the size and density of crystal grains contained in the film are controlled can be formed.

  By the effects described above, a high-quality amorphous Si film used in the present invention and having excellent light stability can be obtained. In the Cat-PECVD method, crystallization can be promoted by the effect of introducing a thermal catalyst even under film forming conditions that were difficult with the conventional PECVD method. Particularly preferred. Here, the origin of the crystallized region in the film is as follows: (1) those caused by the crystallization reaction on the film-forming surface, and (2) Si fine particles (crystal clusters of nanometer size) generated in the plasma space. There are at least two types, which are caused by being taken into the film.

<Substrate temperature>
The substrate temperature is in the range of 100 ° C to 350 ° C. This is because if the substrate temperature is lower than 100 ° C., the hydrogen extraction effect does not work effectively and the hydrogen concentration in the film cannot be reduced effectively.If the substrate temperature is higher than 350 ° C., This is because the desorption of hydrogen becomes remarkable, the dangling bond density in the film increases, and a high-quality film cannot be obtained.

<Raman scattering characteristics>
When describing the structure of an amorphous Si film, the degree of order is often handled. Particularly, short range order (SRO) has a very close relationship with film quality and photostability. It is said that there is. Raman scattering spectroscopy is known as a typical method for evaluating the vibration dynamics of an amorphous network in which the SRO is reflected.

In general, Raman scattering spectrum of amorphous system Si film, TO (horizontal optical vibration) band having a peak near 480 cm ^-1, LO (longitudinal optical vibrations) having a peak near 385cm ^-1 band, 305 cm ^-1 It is composed of an LA (vertical acoustic vibration) band having a peak in the vicinity, and a TA (horizontal acoustic vibration) band having a peak in the vicinity of 160 cm ⁻¹ .

Table 1 shows the Raman scattering measurement spectra of the Si films corresponding to the semiconductor films used in the devices 1 to 4 of the present invention and the conventional devices 1 and 2 for comparison, using the Gaussian type + Lorentzian type approximation curves to indicate the four energy bands described above. scattering peak intensity of TA bands obtained by separating the _{(I TA)} and the scattering peak intensity of tO band _{(I tO)} which is the ratio TA / tO scattering peak intensity ratio of the _(I TA _/ I _tO), the tO band The result of obtaining the half width (HW _TO ) of the scattering peak is shown. Here, for the measurement of the Raman spectrum, a Renishaw Ramanscope System 1000 using a He-Ne laser (wavelength 632.8 nm) as the excitation light was used.

It is known that the distribution width Δθ of the bonding angle θ of Si has a positive correlation with the TA / TO scattering peak intensity ratio (hereinafter, I _TA / I _TO ) or the TO band half-value width (HW _TO ). Have been. Here, looking at I _TA / I _TO , in the films used for the conventional elements 1 and 2, it was I _TA / I _TO = 0.36 and 0.38 (I _TA / I _TO of the conventional amorphous Si film was small. On the other hand, in the films used for the devices 1 to 4 of the present invention, all the films are 0.35 or less, which is smaller than the values of the conventional devices 1 and 2. . Further, it was found that the value of I _TA / I _TO was 0.22 or less, and that a value greatly reduced from the value of the conventional device was obtained. Further, even when viewed with the _{HW TO,} the film used in the conventional device 1, 2, TO band half width 65cm ^-1, whereas it was 68cm ^-1, used in the present invention device 1-4 film It can be seen that the widths were narrower than this, being 64 cm ^-1 and 65 cm ^-1 .

  The above results show that the variation Δθ of the Si bond angle of the films used in the devices 1 to 4 of the present invention is smaller than that of the conventional device, that is, the SRO is improved. It is considered that the structural change (improvement) related to the SRO is a main cause of realizing the photoelectric conversion device of the present invention having a high light stability in which the light deterioration rate is significantly reduced.

In addition, as is clear from the results of the photodegradation rate in Table 1, the above-mentioned SRO improvement effect is observed when I _TA / I _TO is 0.35 or less. When the value is less than 0.28 which is a value between 0.22 and 0.22 of the element 2 of the present invention, and more preferably 0.22 or less of the element 2 of the present invention, a large light deterioration rate is recognized.

<ESR spin density>
Further, in the amorphous Si film used in the device of the present invention, the Si dangling bond density, which is the ESR spin density measured by the electron spin resonance method, is about 3 × 10 ¹⁵ / cm before light irradiation (initial). ³ , which exceeds 5.0 × 10 ¹⁵ / cm ³ for the film used in the conventional device. As described above, in a film having a dangling bond density exceeding 5.0 × 10 ¹⁵ / cm ³ , when applied to an active layer, the recombination current in the same layer increases, and high device characteristics cannot be obtained. In addition, JES-RE3X manufactured by JEOL was used for ESR spin density measurement.

<FT-IR characteristic (Si-H bond state ratio)>
Further, in the amorphous Si film used in the device of the present invention, the existence density of the Si—H (monohydride) bonded state evaluated by FT-IR (Fourier transform infrared spectroscopy) analysis indicates the existence density of the Si—H bonded state. The ratio of the existing density and the existing density in the Si—H ₂ (die hydride) bonding state to the total existing density (hereinafter, referred to as the Si—H bonding state ratio) was 0.97 or more. This Si—H bond state ratio has a large correlation with photodegradation as already described in the description of the related art, and the higher the ratio (the more the Si—H bond is dominant), the higher the light intensity. Deterioration is reduced. In the Si film used in the device of the present invention, the Si-H bond state ratio obtained by the conventional plasma CVD method is about 0.90, which is much larger than 0.95, which is considered to have a remarkable light deterioration suppressing effect. Is obtained. The FT-IR characteristics were measured using FTIR-8300 manufactured by Shimadzu Corporation.

<Hydrogen concentration in film>
The hydrogen concentration in the amorphous Si film used in the device of the present invention was estimated to be about 5 atomic% by FT-IR analysis, and was estimated to be about 10% in the conventional device. At this time, the calculation of the hydrogen concentration in the film was performed using the absorption peak area near 630 cm ⁻¹ and A value = 1.6 × 10 ¹⁹ cm ⁻² . As described above, the Si film used in the device of the present invention has a low hydrogen concentration of 7 atomic% or less, which also seems to contribute significantly to the device of the present invention exhibiting high light stability. If the hydrogen concentration in the film is greater than 7%, the density of the Si—H ₂ bonded state in the film is increased, and the light deterioration rate is increased.

<Optical band gap>
The optical bandgap energy Eg.opt of the amorphous Si film used in the device of the present invention was evaluated to be about 1.6 eV by a so-called cube root plot, and the conventional film was about 1.8 eV. Thus, the optical band gap energy Eg.opt of the Si film used in the device of the present invention was narrowed to 1.7 eV or less, and it was confirmed that the Si film was an amorphous Si film having excellent long-wavelength sensitivity characteristics. Was done. When the optical bandgap energy Eg.opt is larger than 1.7 eV, when the film is used as a photoactive layer, long wavelength light cannot be sufficiently absorbed and photoelectric conversion cannot be performed, and the photocurrent decreases, and the device characteristics are reduced. Leads to a decrease in

<Band gap adjusting element>
The bandgap energy Eg of the amorphous Si film can be adjusted to some extent by the hydrogen concentration in the film. However, when it is desired to adjust the Eg while keeping the hydrogen concentration in the film low, it is necessary to add an Eg adjusting element. Just fine. Specifically, a gas containing a molecular formula such as Ge or Sn for narrow gap or C, N or O for wide gap may be introduced into the film forming space. That, _GeH 4 in case of incorporating the Ge (H contains deuterium _{D), Ge n H 2n +} 2 (n is a positive integer, the same applies hereinafter) of, _GeX 4 (X is a halogen element) such as, containing Sn _SnH 4 in the case of (H contains deuterium _{D), Sn n H 2n +} 2, SnX 4 (X is halogen), _SnR 4 (R is an alkyl group) and the like, CH ₄ in the case of incorporating the C (H includes deuterium D), C ₂ H ₂ , C _n H _{2n + 2} , C _n H _2n , CX ₄ (X is a halogen element), and N ₂ , NO _n , N _When O is contained in ₂ O, NH _3, or the like, O ₂ , CO, CO ₂ , NO _n , N ₂ O, H ₂ O, or the like may be introduced.

<Crystallization rate>
When the amorphous Si film is an amorphous Si film containing nanocrystal grains, the control of the crystallization rate expressed as a volume fraction occupied by the nanocrystal grains in the film is determined by a hydrogen dilution rate ( Gas flow ratio H ₂ / SiH ₄ ), thermal catalyst temperature (Tcat), VHF power density, film forming gas pressure, substrate temperature can be freely performed in the range of 0 to 100%. The rate is adjusted within a range of 30% or less, and more preferably, within a range of 10% or less. If the crystallization ratio exceeds 30%, it becomes difficult to sufficiently exhibit the characteristics as an amorphous system, and the deterioration in characteristics cannot be ignored.

  At this time, the efficiency of the photoelectric conversion element can be further improved by making the crystallization ratio have a gradient distribution, a stepwise distribution, or a periodic distribution in the film thickness direction (not shown). That is, in the case of a slope distribution or a stepwise distribution, the crystallization rate is increased from the light incident side (front side) to the back side.

  By doing so, a band profile in which the optical bandgap energy decreases from the front side to the rear side can be obtained, and effective light absorption can be performed. More efficient photoelectric conversion (that is, higher efficiency) can be performed as compared with the case where the thickness is constant in the thickness direction.

In the case of a periodic distribution, the length of one period is 100 nm or less, preferably 10 nm or less. As a result, a band profile in which the optical band gap energy is periodically modulated can be obtained, and effective light absorption can be performed. Therefore, compared to a case where the optical band gap energy is constant in the film thickness direction. Thus, more efficient photoelectric conversion (that is, higher efficiency) can be performed. In particular, when the period length is set to 10 nm or less, a quantum size effect (formation of a quantum well structure) starts to appear, and higher efficiency can be achieved. Here, the control of the crystallization ratio (that is, reduction by controlling the size and density of nanoclusters in the gas phase) is desirably performed by controlling the temperature of the thermal catalyst. That is, since the temperature control of the thermal catalyst can be performed very quickly and accurately, it is very suitable for controlling the crystallization rate at high speed and accurately during film formation. The crystallization ratio referred to in the present specification is defined as crystal phase peak intensity / (crystal phase peak intensity + amorphous phase peak intensity) in a spectrum obtained by Raman scattering spectroscopy. a peak intensity at a peak intensity + 520 cm ^-1 in crystalline phase peak intensity = 500~510cm ^-1, also intended to peak intensity in the definition of an amorphous phase peak intensity = 480 cm ^-1. The crystallization ratios shown in Table 1 were evaluated by the Raman scattering spectroscopy.

<Crystal size>
Here, when the amorphous Si film used in the present invention is a nanocrystal grain-containing amorphous Si film containing nanosized crystalline Si grains, the nanocrystal grain contained in the amorphous Si film is used. The maximum grain size of the crystal grains is 1 nm or more and 5 nm or less, more preferably 1.5 nm or more and 3 nm or less. If the maximum particle size is smaller than 1 nm, the number of Si atoms constituting the same is too small to significantly reduce the band gap energy of the amorphous Si film, and substantially the same film characteristics as the amorphous Si film It becomes. Further, when the maximum particle size exceeds 5 nm, it becomes difficult to disperse and distribute the particles at appropriate distances in the amorphous phase, and the effect of preferentially causing the recombination of carriers in the crystal grains and the effect of the amorphous phase are considered. The effect of improving the matrix network structure (such as SRO described later) is reduced.

  At this time, the efficiency of the photoelectric conversion element can be further improved by making the existence density distribution or the crystal grain size distribution of the crystal grains have a gradient distribution, a stepwise distribution, or a periodic distribution in the film thickness direction. Not shown). That is, in the case of a gradient distribution or a stepwise distribution, the density distribution of crystal grains or the crystal grain size distribution increases from the light incident side (front side) to the back side. This makes it possible to obtain a band profile in which the optical bandgap energy decreases from the front surface side on the light incident side toward the back surface, and the optical bandgap energy increases in the film thickness direction as described above. Thus, more efficient photoelectric conversion (that is, higher efficiency) can be performed as compared with a fixed case. In the case of a periodic distribution, the length of one period is 100 nm or less, preferably 10 nm or less.

  As described above, it is possible to obtain a band profile in which the optical bandgap energy is periodically modulated. As described above, more efficient photoelectric conversion (compared to the case where the optical bandgap energy is constant in the film thickness direction). That is, high efficiency) can be achieved. In particular, when the period length is set to 10 nm or less, a quantum size effect (formation of a quantum well structure) starts to appear, and higher efficiency can be achieved. Here, it is desirable to control the crystal grains (that is, reduce by controlling the size and density of the nanoclusters in the gas phase) by controlling the temperature of the thermal catalyst. This is because the temperature control of the thermal catalyst can be performed at a very high speed and with high accuracy, which is suitable for controlling the crystal grains at high speed and with high accuracy during film formation.

<Photoelectric conversion device>
Next, an embodiment of the photoelectric conversion device according to the present invention will be described in detail with reference to the drawings, taking a multilayer thin-film Si-based solar cell as an example.

FIG. 1 schematically illustrates a tandem type thin film Si solar cell element having a super straight structure. The thin-film Si solar cell element includes a plurality of photoelectric conversion units each having a photoactive layer as a stacked body, and a photoactive layer of at least one photoelectric conversion unit among the plurality of photoelectric conversion units is obtained by a Raman scattering spectrum. It is composed of an amorphous silicon semiconductor thin film in which the ratio I _TA / I _TO of the scattering peak intensity I _TA of the TA mode to the scattering peak intensity I _TO of the TO mode is 0.35 or less. Further, a plurality of photoelectric conversion units each having a photoactive layer are provided as a laminate, and the photoactive layer of at least one of the plurality of photoelectric conversion units is provided with a TO mode scattering obtained from a Raman scattering spectrum. It is composed of an amorphous silicon semiconductor thin film having a peak half width of 65 cm ^-1 or less. Furthermore, in at least two of the plurality of photoelectric conversion units, the optical band gap of the photoactive layer of the photoelectric conversion unit located on the front side where light is incident is located on the back side of the photoelectric conversion unit. Larger than the optical band gap of the photoactive layer of the photoelectric conversion unit.

  In FIG. 1, 101 is a translucent substrate, 102 is a light receiving surface side electrode, 103 is a semiconductor layer of one conductivity type, 104 is an amorphous Si photoactive layer, 105 is a semiconductor layer of opposite conductivity type, and 106 is light to be incident. Intermediate layer 107, one conductive layer semiconductor layer 107, Si photoactive layer 108, opposite conductive semiconductor layer 109, transparent conductive layer 110, back side electrode 111, and power generation 112 and 113 respectively. An extraction electrode for extracting electric power. The thick arrow in the figure indicates the incident direction of light (hν).

  In manufacturing such a thin-film silicon-based solar cell, first, the translucent substrate 101 is prepared. As the light-transmitting substrate 101, a plate material or a film material made of glass, plastic, resin, or the like can be used.

  Here, it is desirable to form a concavo-convex structure (not shown) on the surface of the light-transmitting substrate 101 on which a thin film to be described later is formed. This uneven structure can function to further promote the light confinement effect described later. As a method of forming the uneven structure, there are an etching method, a blast method, and the like. The maximum height (Rmax) of the uneven shape is set to 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.3 μm or more. The arithmetic mean roughness (Ra) of the uneven shape is set to 0.01 μm or more, more preferably 0.05 μm or more. If necessary, an additional etching process can be performed to obtain a desired uneven shape. As described above, the maximum height (Rmax) and the arithmetic average roughness (Ra) of the concavo-convex shape are set to the above-mentioned ranges, because the scattering effect of incident light is weak below the above ranges, and it is difficult to realize a sufficient light confinement structure. It is. In addition, such an uneven shape can be determined by image processing of a cross-sectional TEM (transmission electron microscope) photograph or surface shape measurement by AFM (atomic force microscope). Is).

Next, a transparent conductive film to be the light receiving surface side electrode 102 is formed. As a material of the transparent conductive film, a known material such as SnO ₂ , ITO, or ZnO can be used. However, when a Si film is formed in a later step, hydrogen caused by using SiH ₄ and H ₂ is used. Since it is exposed to a gas atmosphere, it is desirable to form a ZnO film having excellent reduction resistance at least as a final surface. Known techniques such as a CVD method, a vapor deposition method, an ion plating method, and a sputtering method can be used as a film forming method. The thickness of the light receiving surface side electrode 102 is adjusted in the range of about 60 to several hundreds nm in consideration of the antireflection effect and the reduction in resistance. At this time, the surface of the light receiving surface side electrode 102 is formed into a spontaneous uneven shape by adjusting the forming conditions. The maximum height (Rmax) of the uneven shape is set to 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.3 μm or more. The arithmetic mean roughness (Ra) of the uneven shape is set to 0.01 μm or more, more preferably 0.05 μm or more. If necessary, an additional etching process can be performed to obtain a desired uneven shape. If the maximum height (Rmax) and the arithmetic average roughness (Ra) of the concavo-convex shape are less than the above ranges, the scattering effect of incident light is weak, and it is difficult to realize a sufficient light confinement structure.

  Next, a first photoelectric conversion unit including the hydrogenated amorphous silicon film in the photoactive layer is formed. As the film forming method, the above-described Cat-PECVD method can be used in addition to the plasma CVD (PECVD) method and the catalytic CVD (Cat-CVD) method.

First, the one conductivity type semiconductor layer 103 is formed. That is, a p-type amorphous Si layer having a wide gap and doped with a conductivity type determining element at a high concentration is formed on the light receiving surface side electrode 102. The thickness is adjusted in the range of about 2 to 100 nm. The concentration of a doping element (for example, B (boron)) is set to about 1 × 10 ¹⁸ to 10 ²¹ / cm ³ , and is substantially a p ⁺ type. The Si _x C _1-x film can be obtained by mixing an appropriate amount of a gas containing C (carbon) such as CH ₄ in addition to SiH ₄ and H ₂ used in forming the film and a gas such as B ₂ H ₆ as a doping gas. And is very effective in forming a window layer with small light absorption loss, and also effective in reducing a dark current component for improving an open circuit voltage. A similar effect can be obtained by mixing an appropriate amount of a gas containing O (oxygen) or a gas containing N (nitrogen) in addition to C.

Next, a substantially i-type photoactive layer 104 is formed on the one conductivity type semiconductor layer 3. As the photoactive layer 104, the above-described high-quality and high-stable amorphous Si film formed by the Cat-PECVD method is used. At this time, it is preferable that the film forming conditions are selected within the above-mentioned conditions. In particular, the plasma excitation frequency is 60 MHz, the catalyst temperature is 1600 to 1800 ° C., the H ₂ / SiH ₄ flow ratio is 5 to 10, and the substrate temperature is 200. 250250 ° C., gas pressure 133133200 Pa, RF power density 0.10.10.2 W / cm ² . Under such film forming conditions, the above-described high-quality, high-stable amorphous Si film can be formed at a high film forming rate of 2 nm / sec. Here, since the non-doped film generally shows a slight n-type characteristic, in this case, the non-doped film is adjusted to be substantially i-type by slightly including the p-type doping element. Can be. In some cases, for the purpose of fine adjustment of the internal electric field intensity distribution, an n ^- type or a p ^- type may be used.

  It is desirable that the thickness of the substantially i-type photoactive layer 104 is 0.5 μm or less, more preferably 0.3 μm or less. This is because the amount of light incident on the second photoelectric conversion unit is limited, so that the amount of photocurrent generated by the second photoelectric conversion unit decreases, and as a result, the characteristics of the tandem solar cell deteriorate.

Next, a reverse conductivity type semiconductor layer 105 is formed substantially on the i-type photoactive layer 104. That is, an amorphous Si layer having a wide gap, which is doped with a conductivity type determining element (for example, P (phosphorus)) of a conductivity type opposite to that of the one conductivity type semiconductor layer 103 (that is, n-type), is formed. The thickness is adjusted in the range of about 2 to 100 nm. The doping element concentration is set to about 1 × 10 ¹⁸ to 10 ²¹ / cm ³ , and is substantially an n ⁺ type. In addition, if an appropriate amount of a gas containing C (carbon) such as CH ₄ is mixed in addition to SiH ₄ and H ₂ used for film formation and a gas such as PH ₃ as a doping gas, a Si _x C _1-x film is obtained. As a result, it is possible to form a film with less light absorption loss, and it is also effective in reducing the dark current component for improving the open-circuit voltage. The same effect can be obtained by mixing an appropriate amount of a gas containing N (nitrogen) in addition to C.

In order to further improve the junction characteristics, an i-type layer is substantially formed between the p-type layer (or n-type layer) and the photoactive layer or between the photoactive layer and the n-type layer (or p-type layer). non-single-crystal Si layer and the non-single-crystal _Si x _{C 1-x} layer may be inserted. At this time, the thickness of the insertion layer is about 0.5 to 50 nm. This is because if the thickness is less than 0.5 nm, the effect of improving the junction characteristics cannot be obtained, and if the thickness is more than 50 nm, adverse effects such as a barrier for carrier traveling and a non-negligible resistance component occur.

  Here, in order to realize good recombination characteristics at the junction between the first photoelectric conversion unit and a second photoelectric conversion unit described later (that is, in order to realize ohmic contact-like electrical connection characteristics, It is desirable to increase the crystallization ratio in at least a portion where the opposite conductivity type semiconductor layer 105 and the later-described one conductivity type semiconductor layer 107 are in contact with each other. At this time, if the crystallization ratio is set to 60% or more, tunnel junction characteristics can be obtained, and good reverse junction recombination characteristics can be realized. Note that the crystalline reverse junction is formed by forming a microcrystalline Si layer of the same conductivity type about 5 to 30 nm following the reverse conductivity type semiconductor layer 105 and subsequently forming a microcrystalline Si layer of the opposite conductivity type about 5 to 30 nm. Then, the one-conductivity-type semiconductor layer 107 may be formed, for example, by inserting a dedicated crystalline Si layer independently of the opposite-conductivity-type semiconductor layer 105 and the one-conductivity-type semiconductor layer 107. (Not shown).

  Further, in order to realize an ohmic contact electrical connection characteristic between the first photoelectric conversion unit and the second photoelectric conversion unit, a transparent conductive film, a thin metal layer, or a thin silicide layer (of Si and metal) An alloy layer) may be inserted as the conductive intermediate layer 106. Here, when a transparent conductive film is used, an optical effect (reflection and transmission characteristics) can be introduced by the presence of the transparent conductive film, so that the use of the transparent conductive film is extremely excellent in terms of high efficiency. That is, by adjusting the thickness of the transparent conductive film, short-wavelength light is reflected by the transparent conductive film and re-enters the first photoelectric conversion unit preferentially. Accordingly, the second photoelectric conversion unit can be preferentially confined to the second photoelectric conversion unit, and more efficient photoelectric conversion of light energy becomes possible. The use of this intermediate layer makes it possible to reduce the thickness of the photoactive layer of the first photoelectric conversion unit. This is effective for reducing light deterioration of the unit.

Examples of the material of the transparent conductive film include carbon materials such as silicon oxide materials, silicon carbide materials, silicon nitride materials, and diamond-like carbon in addition to SnO ₂ , ITO, ZnO, and TiO ₂ as metal oxide materials. Can be used. As the film forming method, a known technique such as a CVD method, an evaporation method, an ion plating method, a sputtering method, and a sol-gel method can be used. If necessary, conductivity can be imparted and controlled by adding a material containing an appropriate doping element to a film forming material during film formation.

  The film thickness varies depending on the material, but is appropriately adjusted at about 10 nm to 300 nm.

At this time, among the surfaces of the intermediate layer 106, it is desirable that the surface in contact with at least one photoelectric conversion unit has an uneven shape. In order to form an uneven shape on the interface with the second photoelectric conversion unit, the formation condition of the intermediate layer 106 is adjusted to obtain a spontaneous uneven shape. If necessary, an additional etching process can be performed to obtain a desired uneven shape. In addition, by forming the first photoelectric conversion unit so as to take over the uneven shape of the surface (light receiving surface side electrode 102) on which the first photoelectric conversion unit is formed, the uneven shape is formed at the interface with the first photoelectric conversion unit. Can be formed. The maximum height (Rmax) of the uneven shape is set to 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.3 μm or more. The arithmetic mean roughness (Ra) of the uneven shape is set to 0.01 μm or more, more preferably 0.05 μm or more. This is because if the maximum height (Rmax) and the arithmetic average roughness (Ra) of the concavo-convex shape are less than the above ranges, the scattering effect of incident light is weak and it is difficult to realize a sufficient light confinement structure.

  Next, a second photoelectric conversion unit is formed.

First, a semiconductor layer 107 of one conductivity type opposite to the conductivity type of the semiconductor layer 105 (that is, p-type) is formed. That is, a microcrystalline Si layer doped with a conductivity type determining element at a high concentration is formed on the intermediate layer 106. The thickness is adjusted in the range of about 10 to 100 nm. The doping element concentration is about 1 × 10 ¹⁸ to 1 × 10 ²¹ / cm ³ , and is substantially a p ⁺ -type. Incidentally, it used during film _SiH 4, _{H 2,} and when an appropriate mixture of gas containing C (carbon), such as CH ₄ in addition to the gas such as _B 2 _{H 6} is a doping gas _{Si x C 1-x} A film is obtained, which is very effective for forming a window layer with small light absorption loss, and also effective for reducing a dark current component for improving an open circuit voltage. The same effect can be obtained by mixing an appropriate amount of a gas containing N (nitrogen) in addition to C.

Next, a substantially i-type Si photoactive layer 108 is formed on the one conductivity type semiconductor layer 107. For the Si photoactive layer 108, when using the above-mentioned high-quality and photostable amorphous silicon film formed by using the Cat-PECVD method, the film thickness is adjusted in the range of about 0.5 to 1 μm. When a crystalline Si film typified by a microcrystalline silicon film is used, it is desirable to adjust the film thickness to about 1 to 3 μm. At this time, when using the above-mentioned high-quality and high-stable amorphous Si film, the plasma excitation frequency is 60 MHz, the catalyst temperature is 1600 to 2000 ° C., and the H ₂ / SiH ₄ flow ratio is 5 to 10 μm. The substrate temperature was set to 200 to 250 ° C., the gas pressure was set to 133 to 200 Pa, the VHF power density was set to 0.1 to 0.3 W / cm ² , and the optical band gap was equal to or equal to that of the first photoactive layer. It is desirable that the size be smaller than the photoactive layer. The adjustment of the optical band gap is as described above. When a crystalline Si film is used, the flow rate ratio of H ₂ / SiH ₄ is 5 to 20, the gas pressure is 200 to 665 Pa, and the VHF power density is 0.2 to 0.5 W / cm ² . Under such film forming conditions, the above-described high-quality, high-stable amorphous Si film or crystalline Si film can be formed at a high film forming rate of 2 nm / sec. Here, since the non-doped film usually actually shows a slight n-type characteristic, in this case, it is necessary to include a small amount of the p-type doping element and adjust the film to be substantially i-type. it can. In some cases, for the purpose of fine adjustment of the internal electric field intensity distribution, an n ^- type or a p ^- type may be used. In the case where the crystalline Si film is used for the photoactive layer 108, the film structure is an aggregate of (110) -oriented columnar crystal grains, and the surface shape after film formation is a spontaneous suitable for light confinement. It is desirable to have an uneven structure.

Next, a reverse conductivity type semiconductor layer 109 is formed substantially on the i-type silicon photoactive layer. That is, an amorphous silicon layer or a microcrystalline Si layer in which a conductive type determining element having a conductivity type opposite to that of the one conductivity type semiconductor layer 107 (that is, n-type) is heavily doped is formed. The thickness is adjusted in the range of about 2 to 100 nm. The doping element concentration is set to about 1 × 10 ¹⁸ to 1 × 10 ²¹ / cm ³ , and is substantially n ⁺ type. In addition, if an appropriate amount of a gas containing C (carbon) such as CH ₄ is mixed in addition to SiH ₄ and H ₂ used for film formation and a gas such as PH ₃ as a doping gas, a Si _x C _1-x film is obtained. As a result, it is possible to form a film with less light absorption loss, and it is also effective in reducing the dark current component for improving the open-circuit voltage. A similar effect can be obtained by mixing an appropriate amount of a gas containing O (oxygen) or a gas containing N (nitrogen) in addition to C.

In order to further improve the junction characteristics, an i-type non-conductive layer is formed between the p-type layer (n-type layer) and the photoactive layer or between the photoactive layer and the n-type layer (p-type layer). the single-crystal Si layer and the non-single-crystal _Si x _{C 1-x} layer may be inserted. At this time, the thickness of the insertion layer is about 0.5 to 50 nm.

Further, it is preferable that the formation condition of the opposite conductivity type semiconductor layer 109 is such that a spontaneous uneven structure suitable for light confinement formed on the surface of the microcrystalline Si photoactive layer 108 is left. By the formation conditions of the microcrystalline Si photoactive layer 108 and the opposite conductivity type semiconductor layer 109 described above, the interface between the second photoelectric conversion unit and a second electrode formed above, which will be described later, can be made uneven. . The maximum height (Rmax) of the uneven shape is set to 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.3 μm or more. The arithmetic mean roughness (Ra) of the uneven shape is set to 0.01 μm or more, more preferably 0.05 μm or more. If the maximum height (Rmax) and the arithmetic average roughness (Ra) of the concavo-convex shape are less than the above ranges, the scattering effect of incident light is weak, and it is difficult to realize a sufficient light confinement structure.

  Next, a metal film to be the back electrode 111 as a second electrode is formed. As the metal material, it is desirable to use Al (aluminum), Ag (silver), or the like, which has excellent conductivity and light reflection properties. As the film forming method, known techniques such as an evaporation method, a sputtering method, an ion plating method, and a screen printing method can be used. For example, Ag is deposited by a sputtering method to an appropriate film thickness such that the sheet resistance becomes about 1 Ω / □ or less. Specifically, a sheet resistance of 0.1 Ω / □ or less can be realized by depositing about 1 μm.

As necessary, a transparent conductive layer 110 is formed between the second photoelectric conversion unit and the back surface side electrode 111. The transparent conductive layer 110 is effective for reflecting incident light that has not been absorbed by the second photoelectric conversion unit and causing it to be incident again on the second photoelectric conversion unit, thereby contributing to power generation in the second photoelectric conversion unit. It is. Examples of the material of the transparent conductive layer 110 include carbon materials such as silicon oxide materials, silicon carbide materials, silicon nitride materials, and diamond-like carbon, in addition to SnO ₂ , ITO, ZnO, and TiO ₂ as metal oxide materials. Can be used. As the film forming method, a known technique such as a CVD method, an evaporation method, an ion plating method, a sputtering method, and a sol-gel method can be used. If necessary, conductivity can be imparted and controlled by adding a material containing an appropriate doping element to a film forming material during film formation.

  Although the film thickness varies depending on the material, it is appropriately adjusted at about 10 nm to 100 nm.

At this time, it is desirable that the surface in contact with the back side electrode 111 has an uneven shape. In order to form the uneven shape, the formation condition of the transparent conductive layer 110 is adjusted to obtain a spontaneous uneven shape. If necessary, an additional etching process can be performed to obtain a desired uneven shape. Alternatively, the uneven shape can be formed by forming the transparent conductive layer 110 so as to take over the uneven shape formed by the second photoelectric conversion unit.

  The maximum height (Rmax) of the uneven shape is set to 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.3 μm or more. The arithmetic mean roughness (Ra) of the uneven shape is set to 0.01 μm or more, more preferably 0.05 μm or more. If the maximum height (Rmax) and the arithmetic average roughness (Ra) of the concavo-convex shape are less than the above ranges, the scattering effect of incident light is weak, and it is difficult to realize a sufficient light confinement structure.

  The extraction electrode 112 on the front side and the extraction electrode 113 on the back side, for example, Al, Ag, etc. may be formed on the light receiving surface side electrode 102 using a vacuum film forming technique, a printing and baking technique, and a plating technique. Can be.

<Device characteristics>
Table 1 shows the characteristics (initial characteristics and characteristics or rate of change after the light irradiation test) of the element manufactured as described above in comparison with the conventional example. Here, the light irradiation test is performed under the conditions of irradiating AM1.5 pseudo sunlight (solar simulator light) at a light irradiation intensity of 100 mW / cm ² for 200 hours at a temperature of 48 ± 2 ° C. The stabilization efficiency in Table 1 means the efficiency measured after the light irradiation test. Note that the elements shown in this table are obtained when the photoactive layer 108 of the second photoelectric conversion unit is formed using a microcrystalline Si film.

As can be seen from Table 1, in the device of the present invention, the use of the above-described high-quality and high-stable amorphous Si film makes it possible to form the photoactive layer 104 at a high film-forming rate, but the photo-active layer 104 is high. It has an initial conversion efficiency, and particularly shows a characteristic that the light deterioration rate is extremely lower than that of the conventional device and is greatly reduced to a value of 7% or less. The table also shows that a low photodegradation rate is obtained when the Raman peak intensity ratio TA / TO is 0.35 or less, or the TO band half width is 65 cm ^-1 or less.

  From the above, it has been proved from the device characteristics that the Si film of the present invention has high quality and high light stability.

<Photovoltaic device>
A photovoltaic device can be provided in which the above-described photoelectric conversion device is used as power generation means, and power generated from the power generation means is supplied to a load. That is, one or more of the above-described photoelectric conversion devices (in the case of a plurality of photoelectric conversion devices, these are connected in series, in parallel, or in series-parallel) are used as power generation means (in the case of a plurality of photoelectric conversion devices, these are connected in series, What is connected in parallel or series-parallel is used as the power generating means), and the generated power may be supplied directly to the DC load.

  In addition, the DC power generated by the above-described power generation means is converted into appropriate AC power by power conversion means such as an inverter, and the converted power is converted into an AC load such as a commercial power supply system or various electric devices. A photovoltaic device that can be supplied to

  Further, such a photovoltaic device can be used as a photovoltaic device such as a photovoltaic power generation system of various modes by installing the photovoltaic device on a roof or a wall of a sunny building.

<Generalization>
As described above, the embodiment of the present invention has been exemplified, but the present invention is not limited to the above-described embodiment, and may be in any form without departing from the object of the invention.

  In the above description of the embodiment, an example in which the amorphous Si film of the present invention is applied to a tandem solar cell having two photoelectric conversion units has been described, but a triple having three photoelectric conversion units has been described. The present invention can be applied to a junction type solar cell (not shown) and further to a multi-junction type solar cell (not shown) having a larger number of semiconductor junctions, and similar effects can be obtained. In this case, a solar cell with high efficiency and high photostability can be expected by using two or more photoactive layers, more preferably all the photoactive layers, as the amorphous Si film of the present invention. In a solar cell in which two or more photoelectric conversion units are stacked, the optical band gap of the photoactive layer of the photoelectric conversion unit located on the front side where light is incident is positioned on the back side of the photoelectric conversion unit. By making the optical band gap larger than the optical band gap of the photoactive layer of the photoelectric conversion unit, light absorption is effectively performed.

  Further, as the photoactive layer on the light incident side, amorphous Si of a conventional example can be used.

  Further, a photoelectric conversion unit using a semiconductor substrate can be used as the photoelectric conversion unit on the back side. In this case, as the semiconductor substrate, a single crystal Si substrate, a polycrystalline Si substrate, a GaAs substrate, or the like can be used.

  Further, in the above description of the embodiment, the solar cell in which the semiconductor bonding layer pin is formed in the order of pin from the light receiving surface side has been described. However, the same effect can be obtained with the solar cell formed in the order of nip from the light receiving surface side. .

  Further, the superstrate type solar cell in which light is incident from the substrate side has been described, but the same effect can be obtained for a substrate type solar cell (not shown) in which light is incident from the semiconductor film side. In the case of a substrate type, the substrate is not limited to a light-transmitting substrate, but may be a non-light-transmitting substrate such as stainless steel. The electrodes are made of a light-transmitting material. It is also possible that the substrate also serves as the first electrode.

  Further, the case where the amorphous Si film of the present invention is formed by using the Cat-PECVD method, which is a kind of the PECVD method, has been described. However, the manufacturing method is not limited to this, and the film forming conditions may be adjusted. However, this does not exclude the possibility of formation by the conventional PECVD method. In addition, the possibility of forming by a CVD method other than the PECVD method typified by the Cat-CVD method (catalytic CVD method) by adjusting the film forming conditions is not excluded.

  In addition, although an example in which a high-quality and high-stable amorphous Si film formed by a Cat-PECVD method is used for the photoactive layer of the photoelectric conversion element has been described, the amorphous Si film having the same film characteristics is used. As long as a film can be obtained, there is no particular limitation to the Cat-PECVD method, and another CVD method may be used.

  Further, the amorphous Si film of the present invention can be applied to photoelectric conversion devices such as photodiodes, phototransistors, and optical sensors in addition to solar cells.

<Summary>
As described above, the photoelectric conversion device of the present invention includes a plurality of photoelectric conversion units each having a photoactive layer as a stacked body, and the Raman scattering of the photoactive layer of at least one of the photoelectric conversion units. The ratio of the TA mode scattering peak intensity I _TA to the TO mode scattering peak intensity I _TO obtained from the spectrum, I _TA / I _TO is 0.35 or less. Provided is a highly efficient photoelectric conversion device such as a multi-layer thin-film solar cell or the like which can ensure high reliability because the SRO can be significantly improved and a photoactive layer having low defect density and high light stability can be obtained. Can be.

In addition, the photoelectric conversion device of the present invention includes a plurality of photoelectric conversion units each having a photoactive layer as a laminate, and obtains a photoactive layer of at least one of the photoelectric conversion units from a Raman scattering spectrum. Since the half-width of the scattering peak of the TO mode to be obtained is made of an amorphous silicon semiconductor thin film having a half value width of 65 cm ^-1 or less, the SRO has been greatly improved as compared with the related art, and a low defect density and high light stability have been obtained. Since a photoactive layer can be used, a highly efficient photoelectric conversion device such as a multilayer thin-film solar cell that can ensure high reliability can be provided.

  Further, according to the photovoltaic device of the present invention, the photoelectric conversion device of the present invention is used as power generating means, and the power generated by the power generating means is supplied to the load, thereby providing a high-efficiency photovoltaic device. can do.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically one Embodiment of the multilayer type thin film silicon solar cell of this invention.

Explanation of reference numerals

101: Translucent substrate
102: Light receiving surface side electrode
103: One conductivity type semiconductor layer
104: Amorphous Si photoactive layer
105: reverse conductivity type semiconductor layer
106: Middle class
107: One conductivity type semiconductor layer
108: Si photoactive layer
109: reverse conductivity type semiconductor layer
110: Transparent conductive layer
111: Back side electrode
112, 113: extraction electrode

Claims (4)

A plurality of photoelectric conversion units each having a photoactive layer are provided as a laminate, and the photoactive layer of at least one photoelectric conversion unit among the plurality of photoelectric conversion units is provided with a TO mode scattering peak intensity obtained by a Raman scattering spectrum. A photoelectric conversion device comprising an amorphous silicon semiconductor thin film having a TA mode scattering peak intensity ratio of 0.35 or less. A plurality of photoelectric conversion units having a photoactive layer are provided as a laminate, and the photoactive layer of at least one of the plurality of photoelectric conversion units is set to a half of a TO mode scattering peak obtained from a Raman scattering spectrum. A photoelectric conversion device comprising an amorphous silicon semiconductor thin film having a value width of 65 cm ^-1 or less. In two of the plurality of photoelectric conversion units, the optical band gap of the photoactive layer of one of the photoelectric conversion units located on the light incident side is the optical band of the photoactive layer of the other photoelectric conversion unit. The photoelectric conversion device according to claim 1, wherein the photoelectric conversion device is larger than the gap. A photovoltaic device using the photoelectric conversion device according to any one of claims 1 to 3 as power generation means, and supplying power generated by the power generation means to a load.

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