JP2005064246A - Photoelectric conversion element and manufacturing method thereof, and solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion element that is excellent in photoelectric conversion efficiency. <P>SOLUTION: The photoelectric conversion element comprises a first p-type semiconductor layer 13, a second semiconductor layer (function layer) 14 formed on the first p-type semiconductor layer, and a third n-type semiconductor layer 17 formed on the second semiconductor layer. The second semiconductor layer 14 has a first member 15 comprising a columnar n-type semiconductor nearly vertically formed to the first semiconductor layer, and a second member 16 that is formed while surrounding the first member and contains a p-type semiconductor. The photoelectric conversion element is manufactured by processes. The processes comprise a process for creating a structure having the first columnar member nearly vertical to a substrate and the second member for surrounding the first one on a substrate having a semiconductor layer, a process for eliminating the first member and forming a hole, and a process for filling the hole with an n-type semiconductor material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a photoelectric conversion element and a method for manufacturing the same, and in particular, has a functional nanoporous body having semiconductor characteristics and a functional layer composed of a semiconductor material filled in the porous body, and has high photoelectric conversion efficiency. The present invention relates to a photoelectric conversion element, a manufacturing method thereof, and a solar cell.

  A photoelectric conversion element that converts light energy into electric energy is generally a solar cell using a pn junction or a pin junction of a semiconductor such as silicon or gallium arsenide, and particularly single crystal silicon. Solar cells, polycrystalline silicon solar cells, amorphous silicon solar cells and the like have been put into practical use.

  In the case of a silicon-based solar cell, the manufacturing cost is very low because a mass production process has been established, but the conversion efficiency is lower than that of a solar cell using a compound semiconductor such as gallium-arsenide. This is a problem caused by material properties such as band gap and light absorption coefficient of crystalline silicon and amorphous silicon. For this reason, in order to achieve improved conversion efficiency in crystalline silicon solar cells, the surface reflection is reduced by suppressing the surface reflection by creating a non-reflective coating layer and by creating a texture structure on the light incident surface by anisotropic etching. And device structures have been devised to improve optical confinement (see, for example, Non-Patent Document 1). In addition, amorphous silicon solar cells can be produced uniformly over a large area because there are no grain boundaries, and because there is no lattice matching problem, it is easy to form heterojunctions, compared to crystalline silicon, which is a low energy process. Although the absorption coefficient is about one digit larger, there is an advantage that a thin film can be formed. However, there is a problem that the carrier diffusion length is short and the characteristic deterioration is called a Stebler-Wronski effect.

  Some solar cells using materials other than silicon-based materials use compound semiconductors. Examples of the compound semiconductor include those using III-V group compound semiconductors such as gallium-arsenic (GaAs) and II-VI group compound semiconductors such as cadmium-tellurium (CdTe). Since these are direct transition semiconductors, they have characteristics such as a large absorption coefficient compared to Si, which is an indirect transition semiconductor, and a band gap close to the optimum value for photoelectric conversion. Conversion efficiency is higher than that of Si solar cells. high.

  In recent years, wet solar cells called dye-sensitized solar cells have attracted attention. In particular, a dye-sensitized solar cell called “Gretzel cell” (Non-Patent Document 2) announced by Graetzel et al. Has a relatively high theoretical conversion efficiency and a manufacturing process is a low-energy process. In this solar cell, attempts have been made to improve conversion efficiency by improving sensitizing dyes, semiconductor electrode films, and electrolytes.

Attempts have been made to use porous silicon in which a Si substrate is made porous by anodization in a Si solar cell (for example, Patent Document 1). Porous silicon can control the pore diameter according to anodization conditions, and can reduce the pore diameter to about several nanometers. When porous silicon having such a small pore is used for a photoelectric conversion element, the quantum confinement effect of light and the direct transition semiconductor of Si, which is an indirect transition semiconductor, occur, and the light absorption increases. In addition, since Si present in the pore walls has a quantum wire structure, an effect of increasing carrier mobility can be obtained. These effects contribute to the improvement of photoelectric conversion efficiency. Further, the pore surface of the porous silicon has a lattice spacing slightly widened by hydrogen diffusion during anodization, so that a material having a lattice constant different from Si, for example, GaAs can be heteroepitaxially grown. Heterojunction solar cells using this can also be used.
Japanese Patent Laid-Open No. 06-104463 21th IEEE Photo-voltaic Specialist Conference, (May 21-25 1990), p333-335 Nature, 353, 737 (1991)

  However, in the present situation, substantially sufficient conversion efficiency is not obtained in the photoelectric conversion element using the above-described conventional technology. In addition, in photoelectric conversion elements using porous silicon, attempts have been made to improve the photoelectric conversion efficiency by the quantum size effect, but there are problems such as limitation of substrate material, difficulty in pn junction production, and difficulty in stacking structure. there were.

Therefore, this invention is providing the element with high photoelectric conversion efficiency, such as an open circuit potential and a short circuit current value. In particular, the present invention provides a photoelectric conversion element that solves the problems of a photoelectric conversion element using porous silicon by using a novel functional nanoporous film.
Moreover, this invention is providing the manufacturing method of an element with high photoelectric conversion efficiency, such as an open circuit potential and a short circuit current value. In particular, the present invention provides a method for producing a photoelectric conversion element that solves the problems of a photoelectric conversion element using porous silicon by using a novel functional nanoporous film.

The above problems can be solved by the photoelectric conversion element of the present invention. That is, the first invention according to this application is
A second semiconductor layer formed on the p-type first semiconductor layer;
An n-type third semiconductor layer formed on the second semiconductor layer,
The second semiconductor layer is formed so as to surround a first member made of a columnar n-type semiconductor formed substantially perpendicular to the first semiconductor layer and the first member. It is characterized by having the 2nd member containing.

  In particular, the second member is preferably composed of silicon, germanium, or a mixture of silicon and germanium as a main component excluding oxygen.

  Moreover, it is preferable that a part or all of the second member is crystalline.

  The average diameter of the first member is preferably 1 nm or more and 20 nm or less.

  Furthermore, this invention provides the manufacturing method of the photoelectric conversion element which has said structure.

  That is, the second invention according to the present application includes a step of preparing an electrode on a substrate, a step of preparing a p-type first semiconductor layer on the electrode, a first semiconductor layer on the first semiconductor layer, Preparing a structure in which a columnar substance including one component is dispersed in a member including a second component which is a semiconductor material capable of forming a eutectic with the first component Removing the columnar substance to form a porous body; heat treating the porous body having columnar pores obtained by the removing process; and in the columnar pores of the porous body And a step of preparing a second semiconductor layer by filling an n-type semiconductor material, a step of preparing an n-type third semiconductor layer on the second semiconductor layer, and an electrode on the n-type semiconductor layer And a step of preparing the device.

  In particular, it is preferable that the first component is aluminum and the second component is silicon, germanium, or a mixture of silicon and germanium.

  Moreover, it is preferable that the process of heat-treating the porous body is a heat treatment in a non-oxidizing atmosphere. Here, the non-oxidizing atmosphere is an atmosphere having an oxygen concentration lower than the oxygen concentration in the atmosphere in which a person lives, and an oxygen concentration at which the material is not oxidized. This includes atmospheres that do not contain oxygen. Specifically, the atmosphere is when a film is formed on a substrate in a sealed container such as a sputtering apparatus.

  ADVANTAGE OF THE INVENTION According to this invention, a photoelectric conversion element with higher photoelectric conversion efficiency than before can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The photoelectric conversion element according to the present embodiment includes a p-n junction on the pore wall surface and the porous film surface by filling a functional nanoporous film having p-type semiconductivity with an n-type semiconductor material. The bonding region is increased by forming, and carriers generated by light irradiation are quickly separated. This makes it possible to efficiently prevent minority carrier recombination, resulting in an increase in the short-circuit current value. Also, by optimizing the n-type semiconductor material filled in the porous body, the internal electric field can be increased, and as a result, the open circuit voltage increases.

  In addition, since the pore diameter and pore wall thickness are several nanometers, when the functional nanoporous material is silicon, the absorption coefficient is increased by direct transition of silicon, which is an indirect transition type semiconductor, and the function The carrier mobility can be increased due to the quantum wire structure of the porous nanoporous film and the semiconductor material filled therein.

  In addition, the method for producing a photoelectric conversion element according to the present embodiment can produce a functional nanoporous film having semiconducting electrical conductivity having many pores of several nm by a very simple method. Is perpendicular to the film surface and penetrates, so that a conductive substance can be easily introduced by an electrodeposition method, and the photoelectric conversion element of this embodiment can be manufactured.

  Prior to the description of the embodiments of the present invention, the aluminum silicon structure thin film used in the present embodiment will be described.

(Experimental example 1: first material Al, second material Si)
The aluminum structure part surrounded by silicon is a columnar structure, and an aluminum fine wire having a diameter 2r of 3 nm, an interval 2R of 7 nm, and a length L of 200 nm is shown.

  First, a method for producing an aluminum thin wire will be described.

  An aluminum silicon mixed film containing silicon at 55 atomic% with respect to the total amount of aluminum and silicon is formed on a glass substrate by using an RF magnetron sputtering method. The target used was 8 pieces of 15 mm square silicon chips on a 4 inch aluminum target. Sputtering conditions were as follows: using an RF power source, Ar flow rate: 50 sccm, discharge pressure: 0.7 Pa, and input power: 1 kW. The substrate temperature was room temperature.

  In this example, the target used was eight silicon chips placed on an aluminum target. However, the number of silicon chips is not limited to this, and the composition of the aluminum silicon mixed film varies depending on sputtering conditions. Is about 55 atomic%. The target is not limited to a silicon chip placed on an aluminum target, and an aluminum chip placed on a silicon target may be used, or a target obtained by sintering silicon and aluminum powder may be used. .

  Next, the amount (atomic%) of silicon with respect to the total amount of aluminum and silicon was analyzed by ICP (inductively coupled plasma emission analysis) for the aluminum silicon mixed film thus obtained. As a result, the amount of silicon with respect to the total amount of aluminum and silicon was about 55 atomic%. Here, for convenience of measurement, an aluminum silicon mixed film deposited on a carbon substrate was used as the substrate.

  The aluminum silicon mixed film was observed with an FE-SEM (field emission scanning electron microscope). The shape of the surface viewed from directly above the substrate was a two-dimensional array of circular aluminum nanostructures surrounded by silicon. The pore diameter of the aluminum nanostructure part was 3 nm, and the average center-to-center distance was 7 nm. Moreover, when the cross section was observed with FE-SEM, the height was 200 nm and each aluminum nanostructure part was mutually independent.

  Further, when this sample was observed by an X-ray diffraction method, a silicon peak showing crystallinity could not be confirmed, and the silicon was amorphous.

  Therefore, an aluminum silicon nanostructure including an aluminum fine wire surrounded by silicon and having an interval 2R of 7 nm, a diameter 2r of 3 nm, and a height L of 200 nm could be produced.

(Comparative example)
Further, as a comparative sample A, an aluminum silicon mixed film containing silicon at 15 atomic% with respect to the total amount of aluminum and silicon was formed on a glass substrate by a sputtering method with a thickness of about 200 nm. The target used was a two inch 15 mm square silicon chip on a 4 inch aluminum target. Sputtering conditions were as follows: using an RF power source, Ar flow rate: 50 sccm, discharge pressure: 0.7 Pa, and input power: 1 kW. The substrate temperature was room temperature.

  Comparative sample A was observed with an FE-SEM (field emission scanning electron microscope). The shape of the surface viewed from directly above the substrate was not a circular shape in the aluminum portion but a rope shape. That is, the aluminum columnar structure was not a fine structure uniformly dispersed in the silicon region. Furthermore, its size was far over 10 nm. Moreover, when the cross section was observed with FE-SEM, the width | variety of the aluminum part exceeded 15 nm. The aluminum silicon mixed film thus obtained was analyzed by ICP (inductively coupled plasma emission analysis) for the amount of silicon (atomic%) relative to the total amount of aluminum and silicon. As a result, the amount of silicon with respect to the total amount of aluminum and silicon was about 15 atomic%.

  Further, as a comparative sample B, an aluminum silicon mixed film containing 75 atomic% of silicon with respect to the total amount of aluminum and silicon was formed on a glass substrate by sputtering to a thickness of about 200 nm. The target was a 14-inch aluminum target with 14 15 mm square silicon chips. Sputtering conditions were as follows: using an RF power source, Ar flow rate: 50 sccm, discharge pressure: 0.7 Pa, and input power: 1 kW. The substrate temperature was room temperature.

  Comparative sample B was observed with an FE-SEM (field emission scanning electron microscope). An aluminum portion could not be observed on the sample surface viewed from directly above the substrate. Further, even when the cross section was observed with FE-SEM, the aluminum portion could not be clearly observed. The aluminum silicon mixed film thus obtained was analyzed by ICP (inductively coupled plasma emission analysis) for the amount of silicon (atomic%) relative to the total amount of aluminum and silicon. As a result, the amount of silicon with respect to the total amount of aluminum and silicon was about 75 atomic%.

  Further, the sample in which the comparative sample A is manufactured and the condition of the number of silicon chips is changed, and the ratio of silicon to the total amount of the aluminum silicon mixture is 20 atomic%, 35 atomic%, 50 atomic%, 60 atomic%, and 70 atomic%. Was made. The case where the columnar structure of aluminum is a fine structure uniformly dispersed in the silicon region is indicated by ◯, and the case where it is not indicated by × is shown below.

このように、アルミニウムとシリコンの全量に対するシリコン含有量を、２０ａｔｏｍｉｃ％以上７０ａｔｏｍｉｃ％以下に調整することで、作製されたアルミニウムナノ構造体の径の制御が可能であり、また、直線性に優れたアルミニウム細線の作製が可能になる。なお、構造の確認には、ＳＥＭの他にもＴＥＭ（透過型電子顕微鏡）等を利用するのがよい。なお、上記含有量に関しては上記シリコンに代えてゲルマニウム、あるいはシリコンとゲルマニウムの混合物を用いても同様であった。

Thus, by adjusting the silicon content with respect to the total amount of aluminum and silicon to 20 atomic% or more and 70 atomic% or less, it is possible to control the diameter of the manufactured aluminum nanostructure, and excellent linearity is achieved. Fabrication of an aluminum thin wire becomes possible. For confirmation of the structure, a TEM (transmission electron microscope) or the like may be used in addition to the SEM. The content was the same even when germanium or a mixture of silicon and germanium was used instead of silicon.

  Further, as a comparative sample C, an aluminum-silicon mixed film containing silicon at 55 atomic% with respect to the total amount of aluminum and silicon was formed on a glass substrate by sputtering using a sputtering method. The target used was 8 pieces of 15 mm square silicon chips on a 4 inch aluminum target. Sputtering conditions were as follows: using an RF power source, Ar flow rate: 50 sccm, discharge pressure: 0.7 Pa, and input power: 1 kW. The substrate temperature was 250 ° C.

  Comparative sample C was observed with an FE-SEM (field emission scanning electron microscope). A clear boundary between aluminum and silicon could not be confirmed on the sample surface viewed from directly above the substrate. That is, the aluminum nanostructure could not be confirmed. That is, if the substrate temperature is too high, the state changes to a more stable state, so that it is considered that film growth for forming such an aluminum nanostructure cannot be performed.

  In order to obtain a structure in which columnar members are dispersed, it is also preferable to set the target composition to Al: Si = 55: 45 or the like.

Next, the structure etc. regarding a photoelectric conversion element and its manufacturing method are demonstrated below.
<Regarding Configuration of Photoelectric Conversion Device of the Present Invention>
First, the configuration of the present invention will be described.

  FIG. 1 shows a structural example of a photoelectric conversion element of the present invention. In FIG. 1, 11 is a substrate, 12 is a lower electrode, 13 is a p-type semiconductor layer, 14 is a functional layer, 15 is a first member made of a columnar n-type semiconductor constituting the functional layer 14, and 16 is a functional layer 14. , A second member containing a p-type semiconductor formed so as to surround the first member, 17 is an n-type semiconductor layer, and 18 is an upper electrode.

  First, the second member 16 constituting the functional layer 14 will be described.

  The second member 16 constituting the functional layer 14 includes a columnar substance 21 including the first component shown in FIG. 2A, and a second component that can form a eutectic with the first component. The columnar substance 21 is removed from the structure thin film 23 dispersed in the base material substance 24 that is included. This is shown in FIG. In FIG. 2B, 25 is a porous thin film formed by removing the columnar substance 21, and 26 is a pore from which the columnar substance 21 has been removed. The functional layer 14 is formed by filling the pores 26 of the porous thin film 25 with the material of the first member. The base material part 24 constitutes a second member.

  Here, the columnar substance 21 including the first component is made of, for example, a material mainly composed of aluminum. The base material 24 including the second component that can form a eutectic with the first component is made of, for example, germanium, silicon, or a mixture of germanium and silicon.

  The base material 24 is preferably composed mainly of silicon or germanium. It is also possible to use a mixture of silicon and germanium as a main component. The base material 24 is preferably composed mainly of silicon or germanium, but aluminum (Al), oxygen (O), argon (Ar), nitrogen (N) of several atomic% to several tens atomic%. Various elements such as hydrogen (H) may be contained.

  The base material 24 is preferably partly or entirely crystalline.

  Further, the shape of the pore portion constituting the base material 24 as viewed from the top surface of the substrate may be substantially circular as shown in FIG. 3A, or may be of an arbitrary shape such as an ellipse. .

  In addition, the shape of the pore portion constituting the base material 24 seen from the cross section of the substrate may be a rectangular shape as shown in FIG. 3B, or an arbitrary shape such as a square or a trapezoid.

  In addition, the average diameter 2r of the pores 26 shown in FIG. 3 (b) can be prepared from 0.5 nm to 50 nm, preferably 1 nm to 20 nm. Moreover, there is no restriction | limiting in the film thickness L of a porous thin film, Basically what kind of film thickness may be sufficient.

  Next, the first member 15 made of a columnar n-type semiconductor constituting the functional layer 14 will be described.

The material constituting the columnar n-type semiconductor member 15 may be basically any semiconductor as long as it has n-type conductivity. Examples thereof include IV such as silicon (Si) and germanium (Ge). Group semiconductors, III-V semiconductors such as gallium-arsenic (GaAs), indium-phosphorus (InP), indium-gallium-phosphorus (InGaP), cadmium sulfide (CdS), cadmium-zinc-sulfur (CdZnS), zinc- II-VI group semiconductors such as selenium (ZnSe), cadmium-selenium (CdSe), cadmium-tellurium (CdTe), zinc sulfide (ZnS), zinc oxide (ZnO), copper sulfide (Cu ₂ S), copper-indium -Selenium (CuInSe ₂ : CIS) and the like can be mentioned, but other semiconductors having n-type conductivity may be used. Of the semiconductor materials listed here, semiconductor materials having high photoelectric conversion efficiency are preferable, and specifically, CuInSe ₂ , GaAs, CdTe, InP, and the like are preferable. More preferably, a semiconductor material capable of filling the pores of the porous thin film by an electrodeposition method is preferable.

One columnar member may be composed of a plurality of n-type semiconductor materials. Specifically, a structure as shown in FIG. 4 may be used. In FIG. 4, 41 is a substrate, 42 is a lower electrode, 43 is a p-type semiconductor layer, 442 is a functional layer, 451, 452 and 453 are first members made of columnar n-type semiconductors constituting the functional layer 441, 46 denotes a second member containing a p-type semiconductor formed so as to surround the first member constituting the functional layer 442, 47 denotes an n-type semiconductor layer, and 48 denotes an upper electrode. The first member layers 451, 452, and 453 made of columnar n-type semiconductors are different semiconductor materials, and are preferably semiconductor materials having different band gaps. Examples of such a combination of semiconductor materials include InGaP, GaAs, and InGaAs. With such a configuration, it is expected that the wavelength sensitivity band is expanded and light of different wavelengths can be efficiently absorbed, and the photoelectric conversion efficiency is improved.
<About the manufacturing method of the photoelectric conversion element of this invention>
Next, the manufacturing method of the photoelectric conversion element concerning this invention is demonstrated in detail.

  Each process of one embodiment of the manufacturing method of a photoelectric conversion element is shown below. The manufacturing method of a photoelectric conversion element has the following process (a)-process (h).

Step (a): Step of forming an electrode on a substrate Step (b): Step of forming a p-type semiconductor layer on the electrode Step (c): Containing a first component on the p-type semiconductor layer A step of forming a structure in which the columnar substance is dispersed in a member including the second component which is a semiconductor material capable of forming a eutectic with the first component Step (d): Removal step of removing columnar substance and forming porous body Step (e): Step of heat-treating porous body having columnar pores obtained by the removal step Step (f): Columnar shape of the porous body Step of forming functional layer by filling n-type semiconductor material in pores Step (g): Step of forming n-type semiconductor layer on the functional layer Step (h): Electrode on the n-type semiconductor layer Step of Forming Each step will be described below with reference to FIGS. FIGS. 5A to 5D correspond to the steps (a) to (d), and FIGS. 6E to 6H correspond to the steps (e) to (h), and are cross-sectional views illustrating each configuration. .

Step (a): As shown in FIG. 5A, an electrode 512 is formed on a substrate 511. Any electrode material may be used. Specifically, any metal electrodes such as Al, Ti, Pt, Au, etc., and oxide transparent electrodes such as tin-doped indium oxide (Sn-doped In ₂ O ₃ : ITO) are basically used. However, a material that forms ohmic contact with the p-type semiconductor is preferable. The electrode may be produced by any means such as sputtering or vapor deposition.

Step (b): As shown in FIG. 5B, a p-type semiconductor layer 521 is formed on the electrode 512 formed in the step (a). The p-type semiconductor material may be basically any material as long as it can be formed into a film, but preferably amorphous silicon doped with an acceptor such as boron (B), aluminum (Al), or gallium (Ga). a-Si), hydrogenated amorphous silicon (a-Si: H), or polycrystalline silicon (poly-Si) is preferred. Furthermore, it is more preferable that the concentration of the acceptor in the a-Si, a-Si: H, and poly-Si is 10 ¹⁹ cm ⁻³ or more. Further, the p-type semiconductor material is preferably formed by a CVD method, and more preferably by a plasma CVD method. However, the method is not particularly limited to these methods, and a sputtering method, a liquid phase A film forming method such as a reaction method may be used.

Step (c): As shown in FIG. 5C, the columnar substance 532 including the first component is formed on the p-type semiconductor layer 521 formed in the step (b). And a structure layer 531 dispersed in a base material 533 including a second component which is a semiconductor material capable of forming a eutectic crystal. For example, providing a matrix material (a mixture of or germanium or silicon and germanium,) columnar substance (second component) in the aluminum and silicon to form a (first component), a sputtering method, an electron beam vapor deposition, etc. A mixed film (an aluminum silicon mixed film, an aluminum germanium mixed film, or an aluminum silicon germanium mixed film), which is a structure layer, is formed on the p-type semiconductor layer by a method capable of forming a substance in the non-equilibrium state.

  When an aluminum silicon mixed film (or aluminum germanium mixed film or aluminum silicon germanium mixed film) is formed by such a method, an eutectic structure in which aluminum and silicon (or germanium, or a mixture of silicon and germanium) are metastable. A columnar substance made of aluminum forms a nanostructure (columnar structure) of several nanometers in a base material made of amorphous silicon (or amorphous germanium, or a mixture of amorphous silicon and germanium), and is self-organized. Separate. At that time, the aluminum columnar substance has a substantially cylindrical shape, the pore diameter is 0.5 nm or more and less than 50 nm, and the interval is 3 nm or more and less than 30 nm.

  Note that in a mixed film of aluminum and amorphous silicon (or amorphous germanium, or a mixture of amorphous silicon and germanium), the amount of silicon (or germanium, or a mixture of silicon and germanium) in the formed film is the same as that of aluminum. It is 20 to 70 atomic%, preferably 25 to 65 atomic%, more preferably 30 to 60 atomic%, based on the total amount of silicon (or germanium, or a mixture of silicon and germanium). If the amount of silicon is within such a range, an aluminum-silicon mixed film (or aluminum-germanium mixed film) in which aluminum columnar substances are dispersed in an amorphous silicon (or amorphous germanium, or a mixture of amorphous silicon and germanium) base material. Or an aluminum silicon germanium mixed film).

  The atomic% indicating the ratio of aluminum and silicon (or germanium, or a mixture of silicon and germanium) indicates the ratio of the number of atoms of silicon (or germanium, or a mixture of silicon and germanium) and aluminum, and atom% Alternatively, it is also described as at%. For example, silicon (or germanium, or silicon and germanium) in an aluminum silicon mixed film (or aluminum germanium mixed film or aluminum silicon germanium mixed film) by inductively coupled plasma emission spectrometry (ICP method). It is the value when the amount of aluminum is quantitatively analyzed.

  Step (d): As shown in FIG. 5D, the columnar substance 532 including the first component is removed, and a porous body layer 541 having pores 542 is formed. For example, aluminum that is a columnar substance in the aluminum silicon mixed film (or aluminum germanium mixed film or aluminum silicon germanium mixed film) is removed by etching using phosphoric acid, and the inside of the base material (here, amorphous silicon or A pore is formed in amorphous germanium or a mixture of silicon and germanium in an amorphous state. Thereby, a porous body layer is formed on the p-type semiconductor layer.

  Note that the pores 542 in the porous body layer have an interval of 5 nm or more and less than 20 nm, and a pore diameter of 0.5 nm or more and less than 15 nm.

  The solution used for the etching is preferably an acid that dissolves aluminum and hardly dissolves amorphous silicon (or amorphous germanium, or a mixture of amorphous silicon and germanium), for example, phosphoric acid, sulfuric acid, hydrochloric acid, sulfuric acid, concentrated sulfuric acid, chromic acid. Such as a solution. Furthermore, among the above acids, an acid that does not proceed with oxidation of amorphous silicon (or amorphous germanium, or a mixture of amorphous silicon and germanium) forming the porous body layer is more desirable. For example, concentrated sulfuric acid. However, an alkali such as sodium hydroxide can be used as long as there is no inconvenience in the formation of pores by etching and the oxidation of the porous body layer surface does not proceed, and it is particularly limited to the type of acid and the type of alkali. It is not something. Also, a mixture of several types of acid solutions or several types of alkali solutions may be used. In addition, for example, the etching conditions such as solution temperature, concentration, and time can be appropriately set according to the porous layer to be produced.

  Step (e): As shown in FIG. 6 (e), the porous structure 543 having the pores 542 obtained by the removing step is heat-treated, and the porous structure having the pores 552 and the crystalline porous body layer 551 is obtained. A structure 553 is prepared. For example, the porous structure is subjected to conditions for crystallization of amorphous silicon (or amorphous germanium, or a mixture of amorphous silicon and germanium) constituting the porous layer, for example, heat treatment or laser irradiation. As a result, part or all of the amorphous silicon (or amorphous germanium, or a mixture of amorphous silicon and germanium) is crystallized. As a result, crystalline silicon (or crystalline germanium, or a mixture of crystalline silicon and germanium) is formed in the region of amorphous silicon (or amorphous germanium, or a mixture of amorphous silicon and germanium), and crystalline on the p-type semiconductor layer. A silicon porous body layer (or a crystalline germanium porous body layer or a crystalline silicon germanium porous body layer) is formed. At this time, heat treatment in a highly reducing atmosphere is preferable, and heat treatment in a high concentration hydrogen atmosphere is more preferable. The heat treatment is preferably performed at a temperature of 300 ° C. or higher and 1000 ° C. or lower, more preferably 600 ° C. or higher and 900 ° C. or lower. However, crystallization of amorphous silicon (or amorphous germanium, or a mixture of amorphous silicon and germanium) and crystalline silicon porous layer (or crystalline germanium porous layer or crystalline silicon germanium porous layer) Any method and condition may be used as long as there is no problem in the structure, and several types of methods such as heat treatment and laser irradiation may be used in combination.

  When the p-type semiconductor layer 521 manufactured in the step (b) is an amorphous semiconductor such as a-Si or a-Si: H, the amorphous p-type semiconductor layer may be crystallized by the heat treatment in this step. Absent.

  Step (f): As shown in FIG. 6 (f), the n-type semiconductor material is filled into the columnar pores 552 of the crystalline porous body layer 551, and the n-type semiconductor columnar member 562 and the crystalline porous body are filled. A functional layer 561 including the layer 551 is formed. The method of filling the n-type semiconductor material into the crystalline porous layer may be basically any method, but a method that can fill the n-type semiconductor into the pores without gaps, for example, an electrodeposition method. It is preferable.

  Further, when an oxide layer is formed on the surface of the porous body, it is preferable to remove the oxide layer before filling the pores of the porous body with the n-type semiconductor material. The removal method is preferably, but not limited to, an acid that dissolves silicon oxide such as hydrofluoric acid (HF), but the oxide layer present on the porous body layer surface is removed, and Any method may be used as long as the structure of the porous body layer can be maintained.

  Step (g): As shown in FIG. 6G, an n-type semiconductor layer 571 is formed on the functional layer 561. The n-type semiconductor layer formed in this step may basically use any substance, but if the n-type semiconductor material and the manufacturing method prepared in the step (f) are continuously used in this step, a process is performed. It is convenient and preferable.

  Step (h): As shown in FIG. 6H, an electrode 581 is formed on the n-type semiconductor layer 571. Basically, any electrode material may be used, but it is desirable to use a material that forms ohmic contact with the n-type semiconductor layer 571 underneath. The electrode may be formed by any method such as sputtering or vapor deposition.

  In addition, the surface of the n-type semiconductor layer 571 may be subjected to planarization treatment such as CMP polishing before preparing an electrode in this step.

  In addition, when the substrate 511 and the electrode 512 manufactured in the step (a) have no light transmission property or are very low, the electrode shape should be optimized using a mask or the like when forming the electrode in this step. Is desirable. Specifically, it is desirable that the introduction of light into the photoelectric conversion element is not hindered by the electrode. For example, by forming a patterned electrode such as a finger electrode, a sufficient amount of light is supplied into the element. It is desirable to have a structure that can be introduced.

  However, when the substrate 511 and the electrode 512 manufactured in step (a) sufficiently transmit light, for example, when a glass substrate is used as the substrate 511 and a transparent electrode such as ITO is used as the electrode 512, the electrode shape is basically Any shape may be used, but a shape that covers the entire surface of the n-type semiconductor layer 571 is preferable. Further, when light is emitted from the substrate 511 to the element, the light reaching the boundary surface between the n-type semiconductor layer 571 and the electrode 581 is reflected by the electrode 581 and returned to the element. Preferably it is.

  The above is the configuration of the photoelectric conversion element and the manufacturing method thereof. However, unless the configuration of the photoelectric conversion element and the manufacturing method are significantly changed, in addition to the element configuration, the present silicon solar cell and compound solar Devices for improving the conversion efficiency used in batteries, dye-sensitized solar cells and the like, for example, an antireflection film, a texture structure, a surface passivation structure, etc. may be added to the configuration of the photoelectric conversion element. Moreover, you may add the process of introducing the device for the said conversion efficiency improvement to the said manufacturing method.

  Hereinafter, the present invention will be described using examples.

  In this example, a quartz substrate was used as the substrate material.

Next, an ITO transparent electrode having a thickness of 200 nm was formed on the substrate by sputtering. A p-type amorphous silicon thin film doped with boron (B) was produced thereon using a plasma CVD apparatus. At this time, the doping amount of boron can be controlled by changing the ratio of the source gas SiH ₄ and the doping gas B ₂ H ₆ .

  Next, on the p-type amorphous silicon thin film, an aluminum silicon mixed film containing 56 atomic% of aluminum with respect to the total amount of aluminum and silicon was formed to a thickness of about 100 nm by magnetron sputtering. A circular aluminum silicon mixed target having a diameter of 4 inches (101.6 mm) was used as the target. As the aluminum silicon mixed target, an aluminum powder and silicon powder sintered at a ratio of 56 atomic%: 44 atomic% was used. Sputtering conditions were as follows: RF flow rate, Ar flow rate: 30 sccm, discharge pressure: 0.15 Pa, input power: 100 W. The substrate temperature was 100 ° C.

In addition, the aluminum silicon mixed film was observed with FE-SEM (field emission scanning electron microscope). As a result, as shown in FIG. 2A, the shape of the surface viewed from the obliquely upward direction of the substrate was a two-dimensional array of circular aluminum columnar structures surrounded by silicon regions. The average diameter of the aluminum columnar structure portion was 4 nm, and the average density was 1.5 × 10 ¹¹ cm ⁻² or more. Moreover, when the cross section was observed with FE-SEM, each aluminum columnar structure was mutually independent.

  The aluminum silicon mixed film thus produced was immersed in a 98% concentrated sulfuric acid solution for 24 hours, and only aluminum columnar structure portions were selectively etched to form pores. When the shape was observed with an FE-SEM, it was a film having a large number of pores perpendicular to the film surface as shown in FIG. As a result, a porous film composed of a member whose main component excluding oxygen was silicon was produced. When this porous film was measured with a microscopic Raman spectroscope, it was found to be amorphous silicon.

  Next, the thus produced structure was heat-treated at 600 ° C. for 5 hours in a 100% hydrogen atmosphere at atmospheric pressure to crystallize the p-type amorphous silicon film and the porous film. At this time, the presence of crystalline silicon was confirmed by an X-ray diffractometer and a microscopic Raman spectroscope. Moreover, when the conductivity type of the porous film crystallized by the thermoelectromotive force method was determined, it was found to have p-type conductivity.

The oxide film formed on the surface of the crystallized porous film is removed with 2% hydrofluoric acid (HF), and then cadmium selenide (CdSe) is introduced into the pores of the porous body by electrodeposition. did. The electrolyte used was a solution of cadmium dichloride (CdCl ₂ ) and selenium (Se) in a solvent of 0.05 mol·L ⁻¹ cadmium dichloride (CdCl ₂ ) and dimethyl sulfoxide (DMSO). Electrodeposition was performed at a current temperature of 185 ° C. for 30 minutes at a current density of 0.85 mA · cm ⁻² .

  The film after electrodeposition was surface polished to smooth the surface. When the cross-sectional structure was observed by FE-SEM, it was confirmed that CdSe was filled in the pores of the porous body, and that a CdSe film was formed on the porous film. Further, it was confirmed by X-ray diffraction measurement that CdSe exists as a polycrystal.

  Finally, a titanium-silver (Ti-Ag) electrode was formed on the entire upper surface of the CdSe film by vapor deposition. First, 100 nm of Ti was formed to form ohmic contact, and 300 nm of Ag was formed thereon.

When the photoelectric conversion element thus fabricated was irradiated with 100 mW pseudo sunlight (AM1.5, 100 mW · cm ⁻² ) from the quartz substrate side of the element, a functional layer (porous) as shown in FIG. It was confirmed that the photoelectric conversion efficiency was improved by about 10% as compared with the photoelectric conversion element manufactured by replacing the layer in which the film was filled with CdSe) with the p-type semiconductor layer 64.

  In this example, a quartz substrate was used as the substrate material.

Next, an ITO transparent electrode having a thickness of 200 nm was formed on the substrate by sputtering. A p-type amorphous silicon thin film doped with boron (B) was produced thereon using a plasma CVD apparatus. At this time, the doping amount of boron can be controlled by changing the ratio of the source gas SiH ₄ and the doping gas B ₂ H ₆ .

  Next, an aluminum germanium mixed film containing aluminum at 60 atomic% with respect to the total amount of aluminum and germanium was formed on the p-type amorphous silicon thin film by a magnetron sputtering method to a thickness of about 100 nm. As a target, a circular aluminum germanium mixed target having a diameter of 4 inches (101.6 mm) was used. As the aluminum germanium mixed target, an aluminum powder and a germanium powder were sintered at a ratio of 60 atomic%: 40 atomic%. Sputtering conditions were as follows: RF flow rate, Ar flow rate: 30 sccm, discharge pressure: 0.15 Pa, input power: 100 W. The substrate temperature was 25 ° C.

In addition, the aluminum germanium mixed film was observed with an FE-SEM (field emission scanning electron microscope). As shown in FIG. 2 (a), the shape of the surface seen from the diagonally upward direction of the substrate was a two-dimensional array of circular aluminum columnar structures surrounded by a germanium region. The average pore diameter of the aluminum columnar structure portion was 10 nm, and the average density was 1.5 × 10 ¹⁰ cm ⁻² or more. Moreover, when the cross section was observed with FE-SEM, each aluminum columnar structure was mutually independent.

  The aluminum germanium mixed film thus prepared was immersed in a 98% concentrated sulfuric acid solution for 24 hours, and only aluminum columnar structure portions were selectively etched to form pores. When the shape was observed with an FE-SEM, it was a film having a large number of pores perpendicular to the film surface as shown in FIG. As a result, a porous film composed of a member whose main component excluding oxygen was germanium was produced. When this porous film was measured with a microscopic Raman spectroscope, it was found to be amorphous germanium.

  Next, the thus produced structure was heat-treated at 600 ° C. for 5 hours in a 100% hydrogen atmosphere at atmospheric pressure to crystallize the p-type amorphous silicon film and the porous film. At this time, the presence of crystalline silicon and crystalline germanium was confirmed by an X-ray diffractometer and a microscopic Raman spectroscope.

The oxide film formed on the surface of the crystallized porous film is removed with 2% hydrofluoric acid (HF), and then cadmium selenide (CdSe) is introduced into the pores of the porous body by electrodeposition. did. The electrolyte used was a solution of cadmium dichloride (CdCl ₂ ) and selenium (Se) in a solvent of 0.05 mol·L ⁻¹ cadmium dichloride (CdCl ₂ ) and dimethyl sulfoxide (DMSO). Electrodeposition was performed at a current temperature of 185 ° C. for 30 minutes at a current density of 0.85 mA · cm ⁻² .

  The film after electrodeposition was surface polished to smooth the surface. When the cross-sectional structure was observed by FE-SEM, it was confirmed that CdSe was filled in the pores of the porous body, and that a CdSe film was formed on the porous film. Further, it was confirmed by X-ray diffraction measurement that CdSe exists as a polycrystal.

  Finally, a titanium-silver (Ti-Ag) electrode was formed on the entire upper surface of the CdSe film by vapor deposition. First, 100 nm of Ti was formed to form ohmic contact, and 300 nm of Ag was formed thereon.

When the photoelectric conversion element thus fabricated was irradiated with 100 mW pseudo sunlight (AM1.5, 100 mW · cm ⁻² ) from the quartz substrate side of the element, a functional layer (porous) as shown in FIG. It was confirmed that the photoelectric conversion efficiency was improved by about 15% as compared with the photoelectric conversion element manufactured by replacing the layer filled with CdSe with the p-type semiconductor layer 64.

  In this example, a quartz substrate was used as the substrate material.

Next, an ITO transparent electrode having a thickness of 200 nm was formed on the substrate by sputtering. A p-type amorphous silicon thin film doped with boron (B) was produced thereon using a plasma CVD apparatus. At this time, the doping amount of boron can be controlled by changing the ratio of the source gas SiH ₄ and the doping gas B ₂ H ₆ .

  Next, on this p-type amorphous silicon thin film, an aluminum silicon germanium mixture containing 56 atomic% of aluminum with respect to the total amount of aluminum, silicon and germanium and 50 atomic% of silicon with respect to the total amount of silicon and germanium is formed by magnetron sputtering. A film was formed to a thickness of about 100 nm. As the target, a circular aluminum silicon germanium mixed target having a diameter of 4 inches (101.6 mm) was used. As the aluminum silicon germanium mixed target, an aluminum powder, silicon powder, and germanium powder sintered at a ratio of 56 atomic%: 22 atomic%: 22 atomic% were used. Sputtering conditions were as follows: RF flow rate, Ar flow rate: 30 sccm, discharge pressure: 0.15 Pa, input power: 100 W. The substrate temperature was 25 ° C.

In addition, the aluminum silicon germanium mixed film was observed with FE-SEM (field emission scanning electron microscope). As shown in FIG. 2A, the shape of the surface seen from the obliquely upward direction of the substrate was a two-dimensional array of circular aluminum columnar structures surrounded by silicon germanium regions. The average pore diameter of the aluminum columnar structure portion was 7 nm, and the average density was 5.0 × 10 ¹⁰ cm ⁻² or more. Moreover, when the cross section was observed with FE-SEM, each aluminum columnar structure was mutually independent.

  The aluminum silicon germanium mixed film thus prepared was immersed in a 98% concentrated sulfuric acid solution for 24 hours, and only aluminum columnar structure portions were selectively etched to form pores. When the shape was observed with an FE-SEM, it was a film having a large number of pores perpendicular to the film surface as shown in FIG. As a result, a porous film composed of a member whose main component excluding oxygen was silicon germanium was produced. When this porous film was measured with a microscopic Raman spectroscope, it was found to be amorphous silicon germanium.

  Next, the thus produced structure was heat-treated at 600 ° C. for 5 hours in a 100% hydrogen atmosphere at atmospheric pressure to crystallize the p-type amorphous silicon film and the porous film. At this time, the presence of crystalline silicon and crystalline silicon germanium compound was confirmed by an X-ray diffractometer and a microscopic Raman spectroscope.

The oxide film formed on the surface of the crystallized porous film is removed with 2% hydrofluoric acid (HF), and then cadmium selenide (CdSe) is introduced into the pores of the porous body by electrodeposition. did. The electrolyte used was a solution of cadmium dichloride (CdCl ₂ ) and selenium (Se) in a solvent of 0.05 mol·L ⁻¹ cadmium dichloride (CdCl ₂ ) and dimethyl sulfoxide (DMSO). Electrodeposition was performed at a current temperature of 185 ° C. for 30 minutes at a current density of 0.85 mA · cm ⁻² .

  The film after electrodeposition was surface polished to smooth the surface. When the cross-sectional structure was observed by FE-SEM, it was confirmed that CdSe was filled in the pores of the porous body, and that a CdSe film was formed on the porous film. Further, it was confirmed by X-ray diffraction measurement that CdSe exists as a polycrystal.

  Finally, a titanium-silver (Ti-Ag) electrode was formed on the entire upper surface of the CdSe film by vapor deposition. First, 100 nm of Ti was formed to form ohmic contact, and 300 nm of Ag was formed thereon.

When the photoelectric conversion element thus produced was irradiated with 100 mW pseudo sunlight (AM1.5, 100 mW · cm ⁻² ) from the quartz substrate side of the element, a functional layer (porous) as shown in FIG. It was confirmed that the photoelectric conversion efficiency was improved by about 12% as compared with the photoelectric conversion element manufactured by replacing the layer in which the film was filled with CdSe with the p-type semiconductor layer 64.

  The present invention can be applied to a photoelectric conversion element such as a solar cell using a semiconductor such as silicon or germanium.

It is the schematic which shows the structural example of the photoelectric conversion element of this invention. It is the schematic of the porous thin film formed by removing a columnar substance from the structure thin film comprised from the columnar substance and base material which comprises the functional layer of this invention, and the said structure thin film. It is the schematic explaining the porous thin film which comprises the functional layer of this invention. It is the schematic which shows the other structural example of the photoelectric conversion element of this invention. It is the schematic which shows an example of the manufacturing method of the photoelectric conversion element of this invention. It is the schematic which shows an example of the manufacturing method of the photoelectric conversion element of this invention. It is the schematic of the photoelectric conversion element used for the performance comparison with the photoelectric conversion element of this invention.

Explanation of symbols

11, 22, 41, 511, 61 Substrate 12, 42, 62 Lower electrode 18, 48, 66 Upper electrode 512, 581 Electrode 13, 43, 521, 64 p-type semiconductor layer 63 p ⁺ -type semiconductor layer 17, 47, 571 , 65 n-type semiconductor layer 562 n-type semiconductor material 14, 561 functional layer 441 functional layer 442 functional layer 15 first member 451 first member layer 452 first member layer 453 first member layer 16, 46 second 21, 532 Columnar material 23 Structure thin film 24, 533 Base material 25, 541 Porous thin film 26, 542, 552 Pore 531 Structure layer 543, 553 Porous structure 551 Crystalline porous structure

Claims (9)

a p-type first semiconductor layer;
A second semiconductor layer formed on the p-type first semiconductor layer;
An n-type third semiconductor layer formed on the second semiconductor layer,
The second semiconductor layer is formed so as to surround a first member made of a columnar n-type semiconductor formed substantially perpendicular to the first semiconductor layer and the first member. The photoelectric conversion element characterized by including the 2nd member containing this. 2. The photoelectric conversion element according to claim 1, wherein the component excluding oxygen of the second member is silicon, germanium, or a mixture of silicon and germanium. The photoelectric conversion element according to claim 1, wherein a part or all of the second member is crystalline. 4. The photoelectric conversion element according to claim 1, wherein an average diameter of the first member is 20 nm or less. 5. The photoelectric conversion element according to claim 1, wherein the third semiconductor layer and the first member are formed by the same process. The solar cell using the photoelectric conversion element of any one of Claims 1-5. Forming a structure including a columnar first member substantially perpendicular to the substrate and a second member surrounding the first member on the substrate having the semiconductor layer; removing the first member; And a step of filling the hole with an n-type semiconductor material. A method for manufacturing a photoelectric conversion element, comprising: The method for producing a photoelectric conversion element according to claim 7, wherein the component excluding oxygen of the second member is silicon, germanium, or a mixture of silicon and germanium. The method for manufacturing a photoelectric conversion element according to claim 7, further comprising a step of heat-treating the structure in a non-oxidizing atmosphere after the step of removing the first member and forming the hole.

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