JP4365636B2 - Integrated photoelectric conversion device - Google Patents

Description

【００７８】
このように、本発明により特性と歩留まりの双方が向上していることがわかる。これは、本発明の構成により、半導体光電変換ユニット同士のｐｎ逆接合部における横方向リークを低減できたためと考えられる。
【００７９】
また、ＳＩＭＳにより、発電領域１１０のｐｎ逆接合部１０８と低濃度ドープ領域１０９のドーピング元素濃度の測定を行ったところ、低濃度ドープ領域１０９においては、発電領域１１０のｐｎ逆接合部１０８の１／１０以下となっているときに最も良好な素子特性、歩留まりが得られた。
【００８０】
さらに、レーザー照射により形成された低濃度ドープ領域は、ｐ型ドーピング元素であるＢと、ｎ型ドーピング元素であるＰの双方が観測され、いずれも一方の半導体層から他方の半導体層へと拡散し、濃度勾配が生じていることがわかった。このように双方のドーピング元素が拡散した低濃度ドープ領域を有する試料については、いずれも良好な素子特性、歩留まりが得られていた。
【００８１】
なお、ＳＩＭＳ測定は、ドーピング元素のうち、Ｂについては１次イオン源としてＯ^２＋を用い、Ｐについては１次イオン源としてＣｓ^＋を用いた。また、元素濃度を見積もるにあたっては、分析目的領域内の異なる点を５箇所測定してその平均をとることで行った。
【００８２】
【発明の効果】
本発明の集積型光電変換装置によれば、ｐｎ逆接合部における横方向リークの原因となっている多数キャリア密度を有効に低減させることができ、その結果として、横方向リークを低減させ、高い効率、高い歩留まりを実現することができる。
【００８３】
さらに、低濃度ドープ領域を、半導体分割溝の両側に設けるようにしたので、半導体分割溝の両側の発電領域それぞれに対してｐｎ逆接合部を介しての前記横方向リーク電流の抑制を実現することができ、特性を安定させて高い歩留まりを得る効果をより一層強めることができる。
【００８４】
また、低濃度ドープ領域におけるドーピング元素濃度は、発電領域におけるドーピング元素濃度の１／１０以下としたので、ｐｎ逆接合部における横方向リークを充分に低減することができる。
【００８５】
さらに、低濃度ドープ領域において、相互に逆の導電性を有する２つの半導体層に含有されるドーピング元素が、相手の半導体膜に相互に拡散した構造としたことから、これらの元素同士がドーピング特性を互いに相殺し合わせるため、多数キャリア密度を極めて有効に低減させ、横方向リークを低減させ、より高い効率、より高い歩留まりを得ることができる。
【００８６】
さらに、低濃度ドープ領域は、レーザー照射により形成したので、工程の複雑化、コストアップを招くことなく、容易に本発明の構造を形成することができる。
【図面の簡単な説明】
【図１】本発明に係る集積型光電変換装置の構造を説明するための図である。
【図２】従来の集積型光電変換装置の一構造を説明するための図である。
【図３】従来の集積型光電変換装置の他の構造を説明するための図である。
【図４】従来の集積型光電変換装置の他の構造を説明するための図である。
【符号の説明】
１０１：透光性基板
１０２：表電極層
１０３：表電極分割溝
１０４：タンデム型半導体光電変換層
１０４ａ：第１の半導体光電変換ユニット
１０４ｂ：第２の半導体光電変換ユニット
１０５：半導体層分割溝
１０６：裏電極層
１０７：裏電極分割溝
１０８：ｐｎ逆接合部
１０９：低濃度ドープ領域
１１０：発電領域
１１１：非発電領域
１１２：接続導体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an integrated photoelectric conversion device such as a thin film solar cell element in which a plurality of power generation regions are formed on an insulating substrate and connected in series to each other.
[0002]
[Prior art]
In order to use solar energy, solar cells that directly convert light energy into electrical energy have begun to spread. Crystalline solar cells such as single crystal silicon and polycrystalline silicon are used for outdoor power solar cells. Has already been put to practical use. On the other hand, thin film solar cells using polycrystalline thin film silicon, amorphous silicon, chalcopyrite structure semiconductors, etc. are attracting attention because they require less material and are low in cost.
[0003]
Thin film solar cells generally adopt an integrated structure in order to suppress the influence of series resistance. This is because the output characteristics are low current x high voltage due to the use of an integrated structure, and the current is smaller than the high current x low voltage without the integrated structure. This is because the decrease in the fill factor FF can be reduced.
[0004]
On the other hand, a multi-junction element structure in which a plurality of semiconductor photoelectric conversion units are stacked is highly promising for high efficiency. For example, in a Si-based thin film solar cell, an amorphous semiconductor photoelectric conversion unit using hydrogenated amorphous silicon (a-Si: H) as a photoactive layer, and a microcrystalline silicon (μc-Si: H) as a photoactive layer. A tandem type in which stacked crystalline semiconductor photoelectric conversion units are well known, and recently, a triple junction type in which any one of the semiconductor photoelectric conversion units is added and three semiconductor photoelectric conversion units are stacked has been developed. It is being advanced.
[0005]
FIG. 2 shows a structure of a tandem type integrated photoelectric conversion device in which two semiconductor photoelectric conversion units are stacked as an example of an integrated photoelectric conversion device using a conventional multi-junction element. 2, 101 is a translucent substrate, 102 is a surface electrode layer, 103 is a surface electrode dividing groove, 104 is a tandem semiconductor photoelectric conversion layer in which two semiconductor photoelectric conversion units are stacked, and 104a is a pin junction. First semiconductor photoelectric conversion unit having hydrogenated amorphous silicon in the photoactive layer, 104b is a second semiconductor photoelectric conversion unit having a pin junction and having microcrystalline silicon in the photoactive layer, 105 is a semiconductor layer dividing groove, and 106 is A back electrode layer, 107 is a back electrode dividing groove, and 108 is a semiconductor layer having reverse conductivity, that is, an n-type semiconductor layer of the first semiconductor photoelectric conversion unit 104a and a p-type semiconductor of the second semiconductor photoelectric conversion unit 104b. A pn reverse junction where the layers are joined, 110 is a power generation region, 111 is a non-power generation region, and 112 is a connection conductor.
[0006]
The photoelectric conversion cell, which is a power generation region divided by the division groove composed of the front electrode division groove 103, the back electrode division groove 107, and the semiconductor layer division groove 105, is adjacent to the connection conductor 112 arranged in the semiconductor layer division groove 105. The front electrode layer 102 and the back electrode layer 106 of the photoelectric cells to be connected are connected in series.
[0007]
Here, if light enters from the translucent substrate 101 side, the light is transmitted through the surface electrode layer 102 made of a transparent conductor, and photoelectric conversion is performed in the first semiconductor photoelectric conversion unit 104a and the second semiconductor photoelectric conversion unit 104b. And photovoltaic power is generated. In particular, since the first semiconductor photoelectric conversion unit 104a includes hydrogenated amorphous silicon in the photoactive layer, the first semiconductor photoelectric conversion unit 104a has high light absorption characteristics with respect to short-wavelength light. Since the porous silicon film is included in the photoactive layer, it has high light absorption characteristics up to long wavelength light. Therefore, photoelectric conversion is possible over a wide wavelength range of incident light, and the conversion efficiency of the entire apparatus can be improved.
[0008]
[Patent Document 1]
Japanese Patent Publication No.7-114292
[0009]
[Patent Document 2]
JP-A-7-86623
[0010]
[Patent Document 3]
JP 2001-313272 A
[0011]
[Problems to be solved by the invention]
In such a multi-junction element that uses two or more semiconductor photoelectric conversion units in an overlapping manner, when an integrated structure is adopted, a lateral direction through a pn reverse junction where the semiconductor photoelectric conversion units are bonded to each other is used. Leakage becomes a problem. Usually, a pn reverse junction in a multi-junction element has a very high doping concentration (usually 1 × 10 6) in order to enhance electrical connection characteristics between stacked semiconductor photoelectric conversion units, that is, recombination characteristics of majority carriers. ¹⁸ / Cm ³ Above). Therefore, the majority carrier concentration is very high in this pn reverse junction, and it is very easy to conduct in the lateral direction (horizontal direction), especially in the state of working as a low resistance layer that is almost metallic in a highly doped state. It has become.
[0012]
Therefore, in the conventional element structure shown in FIG. 2, the pn reverse junction 108 having a high concentration of doping functions as a lateral leakage path, and the front electrode layer 102 and the pn reverse junction 108 or the back electrode layer 106 and the pn reverse junction. The problem that the part 108 is short-circuited (that is, the top cell or the bottom cell is short-circuited) is unavoidable, resulting in a decrease in the open circuit voltage Voc and the fill factor FF, and a resulting decrease in yield.
[0013]
With respect to this problem, for example, a method of insulating by oxidizing the wall surface of the semiconductor layer dividing groove 105 (see Patent Document 1), or a method of interposing an insulator so as to cut the pn reverse junction portion vertically (Patent Document 2). For example). These are shown in FIGS. 3 and 4, respectively. Here, 301 in FIG. 3 is an insulating layer formed by oxidation or the like, 401 in FIG. 4 is an insulator, and the rest is the same as FIG.
[0014]
However, the method disclosed in Patent Document 1 requires special environmental preparation such as the need for an oxidizing atmosphere in laser processing when forming the semiconductor layer dividing groove 105, and the insulation quality of the oxide layer is very high. Unstable and reliable leak prevention was a very difficult situation.
[0015]
In addition, the method disclosed in Patent Document 2 can realize highly reliable leak prevention, but has a problem in that the formation of an insulator is necessary, so that the process becomes complicated and cost increase cannot be avoided. There has also been a problem that the presence of the insulating film adversely affects the film quality when the semiconductor film is formed.
[0016]
The present invention has been made in view of such problems, and can achieve a high efficiency and a high yield by reducing lateral leakage at the pn reverse junction without causing process complexity and cost increase. An object of the present invention is to provide an integrated photoelectric conversion device that can perform the above-described process.
[0017]
[Means for Solving the Problems]
In view of the above, the integrated photoelectric conversion device of the present invention is a multi-junction semiconductor layer in which two or more semiconductor photoelectric conversion units having a surface electrode layer and a photoelectric conversion function are stacked on a light-transmitting substrate. and A surface electrode dividing groove provided on the surface electrode layer by a laminate formed by sequentially laminating back electrode layers , The semiconductor layer dividing groove provided in the multi-junction semiconductor layer and the back electrode dividing groove provided in the back electrode layer are divided into a plurality of power generation regions, and the front electrode layer and the back electrode layer of the adjacent power generation region are divided into the semiconductor In an integrated photoelectric conversion device connected in series with each other through a connecting conductor through a layer dividing groove,
The dividing grooves provided in each layer are shifted from each other so that the semiconductor layer dividing grooves provided in the multi-junction semiconductor layer are located in a non-power generation region sandwiched between the front electrode dividing grooves and the back electrode dividing grooves. Provided,
The semiconductor photoelectric conversion unit includes a one-conductivity-type semiconductor film and a reverse-conductivity-type semiconductor film, and both adjacent semiconductor photoelectric conversion units form a pn reverse junction where the opposite-conductivity-type semiconductor films are in contact with each other. So
Within the non-power generation area In part of the pn reverse junction, pn reverse junction doping element Diffused vertically A lightly doped region is provided.
[0018]
By adopting such a configuration, since the majority carrier density is reduced in the pn reverse junction of the lightly doped region, the majority carrier is interposed between the lightly doped region and the external heavily doped region. A potential barrier serving as a flow barrier is formed, so that the leakage current in the lateral direction is less likely to flow, so that the efficiency of the integrated photoelectric conversion device can be increased and the characteristics can be stabilized to obtain a high yield.
[0019]
Further, if the lightly doped region is provided on both sides of the semiconductor dividing groove, the lateral leakage current can be suppressed via the pn reverse junction with respect to each of the power generation regions on both sides of the semiconductor dividing groove. Therefore, the effect of stabilizing the characteristics and obtaining a high yield can be further enhanced.
[0020]
In the integrated photoelectric conversion device of the present invention, the doping element concentration in the lightly doped region is not more than 1/10 of the doping element concentration in the pn reverse junction outside the lightly doped region and at least in the power generation region. It is characterized by being.
[0021]
By adopting this configuration, the effect of the potential barrier formed between the low-concentration doped region and the external high-concentration doped region is further ensured, the majority carriers are effectively reduced, and the object of the present invention is achieved. Can be achieved.
[0022]
In the integrated photoelectric conversion device according to the present invention, at least two kinds of doping elements contained in the semiconductor films having opposite conductivity types constituting the pn reverse junction portion are mutually connected in the lightly doped region. It is characterized by diffusing into the semiconductor film.
[0023]
Thus, in the lightly doped region of the pn reverse junction, the p-type doping element and the n-type doping element that work as opposite conductivity types are diffused and present in the mutual semiconductor film, so that the doping element concentration At the same time as these decrease, these elements cancel each other out doping characteristics, so that the majority carrier density can be reduced extremely effectively and the object of the present invention can be achieved.
[0024]
The integrated photoelectric conversion device of the present invention is characterized in that the lightly doped region of the integrated photoelectric conversion device of the present invention is formed by laser irradiation.
[0025]
In this way, by irradiating the pn reverse junction in the heavily doped region with laser, it is heated locally, and the doping element is diffused from the heavily doped region in the vertical direction in the semiconductor layer. A concentration doped region can be formed. Further, not only simple diffusion of the doping element, but also a structure in which the p-type doping element and the n-type doping element that work as opposite conductivity types in the pn reverse junction can be formed simultaneously, so that by laser irradiation, The formed lightly doped region can reduce the majority carriers very effectively and achieve the object of the present invention.
[0026]
In the present invention, the concentration of the doping element can be determined by SIMS (secondary ion mass spectrometry), and the concentration value is measured at five or more different points in the region to be analyzed, and the average value is adopted. Shall.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of an integrated photoelectric conversion device according to the present invention will be described in detail with reference to the drawings.
[0028]
FIG. 1 shows a structure of a tandem integrated photoelectric conversion device in which two semiconductor photoelectric conversion units are stacked as an example of an integrated photoelectric conversion device using a multi-junction element.
[0029]
Here, in FIG. 1, 101 is a translucent substrate, 102 is a surface electrode layer, 103 is a surface electrode dividing groove, 104 is a tandem semiconductor photoelectric conversion layer, 104a is a first semiconductor photoelectric conversion unit, and 104b is a second electrode Semiconductor photoelectric conversion unit, 105 is a semiconductor layer dividing groove, 106 is a back electrode layer, 107 is a back electrode dividing groove, 108 is a pn reverse junction (pn reverse junction of a highly doped region), 109 is a lightly doped region A pn reverse junction, 110 is a power generation region, 111 is a non-power generation region, and 112 is a connection conductor.
[0030]
The translucent substrate 101 is made of glass, on which SnO ₂ A surface electrode layer 102 made of a transparent conductor such as is formed. A first semiconductor photoelectric conversion unit 104a having a pin structure containing hydrogenated amorphous silicon and a second semiconductor photoelectric conversion unit 104b having a pin structure containing crystalline silicon are stacked. At this time, the n-type semiconductor layer of the first semiconductor photoelectric conversion unit 104a and the p-type semiconductor layer of the second semiconductor photoelectric conversion unit 104b are joined to each other to form a pn reverse junction 108. The pn reverse junction 108 has an electrical connection characteristic (majority carrier recombination characteristic) of 1 × 10 ¹⁸ / Cm ³ This is a very high concentration doped region.
[0031]
Further, the front electrode dividing groove 103, the back electrode dividing groove 107, and the semiconductor layer dividing groove 105 have a role as a dividing groove for dividing the stacked body having a photoelectric conversion function stacked on the light-transmitting substrate 101. Thus, the stacked body is divided, and a plurality of photoelectric conversion cells are formed on the light-transmitting substrate 101.
[0032]
The semiconductor layer dividing groove 105 is formed so that the surface electrode layer 102 is exposed inside, and the connection electrode 112 disposed in the semiconductor layer dividing groove 105 is used to connect the surface electrode layer between adjacent photoelectric cells. 102 and the back electrode layer 106 are connected in series. The connection conductor 112 is often formed as a part of the back electrode layer 106 by forming the back electrode layer 106 so as to fill the inside of the semiconductor layer dividing groove 105.
[0033]
The power generation region 110 has a photoelectric conversion function in the photoelectric conversion cell, and is a portion where the converted electric energy is effectively used. The front electrode layer 102 and the back electrode layer 106 in one element are optically connected. This corresponds to the overlapping portion when viewed from the incident side. On the other hand, the non-power generation area 111 corresponds to a portion other than the power generation area 110. In FIG. 1, a portion sandwiched between the front electrode dividing groove 103 and the back electrode dividing groove 107 with the semiconductor layer dividing groove 105 interposed therebetween corresponds, and this portion is a portion that generates photoexcited carriers when light is incident. However, since the electrical energy obtained by photoelectric conversion is not effectively used because the connection conductor 112 is in a short-circuited state, rather, if the area ratio of the entire element of the non-power generation region 111 is large, the photocurrent (power generation) The presence of the photocurrent generated in the region is opposite to the circuit in the circuit) has the effect of reducing the short-circuit current value Jsc of the element. Note that, for the purpose of illustration, the non-power generation region 111 is illustrated as being extended horizontally, but in fact, the non-power generation region 111 is 5 to 5% of the total area of the power generation region 110 so as to increase efficiency as much as possible. It is made small to be about 10% or less.
[0034]
Here, in the present invention, in the non-power generation region 111, In part of the pn reverse junction 108, There is a low-concentration doped region 109 in which the doping element concentration of the pn reverse junction 108 is lower than the doping element concentration of the pn reverse junction 108 in the power generation region 110. A specific operation of the integrated photoelectric conversion device having the configuration will be described.
[0035]
First, if light enters from the translucent substrate 101 side, the light passes through the surface electrode layer 102 made of a transparent conductor, and is photoelectrically converted in the first semiconductor photoelectric conversion unit 104a and the second semiconductor photoelectric conversion unit 104b. Photovoltaic power is generated. In particular, since the first semiconductor photoelectric conversion unit 104a includes hydrogenated amorphous silicon in the photoactive layer, the first semiconductor photoelectric conversion unit 104a has high light absorption characteristics with respect to short-wavelength light. Since the porous silicon film is included in the photoactive layer, it has high light absorption characteristics up to long wavelength light. Therefore, photoelectric conversion is possible over a wide wavelength range of incident light, and the conversion efficiency of the entire apparatus can be improved.
[0036]
Then, the front electrode layer 102 and the back electrode layer 106 of the adjacent photoelectric cells are connected in series by the connection conductor 112 disposed in the semiconductor layer dividing groove 105, and a necessary voltage can be obtained.
[0037]
Here, in the conventional structure, the pn reverse junction portion 108 that has become a highly doped region and the connection conductor 112 in the dividing groove come into contact with each other, causing a leak in the lateral direction and deteriorating element characteristics. On the other hand, in the present invention, the doping element concentration of the pn reverse junction 108 in the non-power generation region 111 is in the non-power generation region 111 from the end of the power generation region 110 of the photoelectric conversion cell to the connection conductor 112 in the dividing groove. Since there is a lightly doped region 109 that is lower than the doping element concentration of the pn reverse junction 108 in the power generation region 110, the lightly doped region 109 and the heavily doped region outside that region are between A potential barrier serving as a barrier for the majority carrier flow is formed, and there is an effect that the leakage current in the lateral direction is difficult to flow. As a result, the integrated photoelectric conversion device to which the present invention is applied has high efficiency and stable characteristics, so that a high yield can be obtained.
[0038]
An example of a process for realizing such an integrated photoelectric conversion device according to the present invention will be described below. In the following, a case where a Si-based film is used for the photoelectric conversion unit (thin film Si-based solar cell) will be described as an example. However, even when other materials are used, there is no essential difference in the effectiveness of the present invention. .
[0039]
First, a translucent substrate 101 is prepared. Here, as the light-transmitting substrate 101, a plate material or a film material made of glass, plastic, resin, or the like can be used.
[0040]
Next, the surface electrode layer 102 is formed over the light-transmitting substrate 101. A known oxide transparent conductive film can be used as the surface electrode layer 102. Specifically, SnO that is tin oxide ₂ A material such as ITO, which is indium-tin oxide, or ZnO, which is zinc oxide, can be used. Note that the transparent conductive film is formed of SiH when a Si film is formed on this film later. ₄ And H ₂ Therefore, it is desirable to form a ZnO film excellent in reduction resistance as at least the final surface. As a film forming method, a known technique such as a CVD method, a vapor deposition method, an ion plating method, a sputtering method, a spray method, and a sol-gel method can be used. The film thickness of the transparent conductive film is adjusted in the range of about 60 to 600 nm in consideration of the antireflection effect and low resistance. As a standard for lowering the resistance, it is desirable that the sheet resistance is about 10 Ω / □ or less.
[0041]
Next, a patterning process for forming the surface electrode dividing groove 103 is performed on the surface electrode layer 102. Thereby, the surface electrode layer 102 is divided into a plurality of regions (a plurality of device regions). At this time, it is desirable to process and form the surface electrode dividing groove 103 by a laser scribing method. At this time, for example, a YAG fundamental wave (wavelength: 1.06 μm) is used as the laser, and the power is adjusted by the thickness of the surface electrode layer 102. For example, SnO as the surface electrode layer 102 ₂ Is set to 500 nm, the laser power may be adjusted within a range of about 1 to 4 W at the processing point. The processing width is about 50 to 100 μm. Also, laser irradiation is from the glass surface side, and the glass surface side is gravitationally upward (that is, the film surface side is gravitationally downward), so that ablation debris generated during laser processing It is desirable to make it difficult to adhere to the film surface (surface on which the device is manufactured) (this is preferably applied in any of the laser processing steps described below).
[0042]
The surface electrode dividing groove 103 can be formed by a wet etching method using an acid solution in addition to the laser scribe method. For example, SnO ₂ Zn wet ZnO for wet etching ₂ If the hydrochloric acid HCl is sprayed in a mist form on the film uniformly sprayed, a large amount of active hydrogen is generated by the reaction between Zn and HCl, which is SnO. ₂ Is reduced to metal Sn, and the metal Sn is dissolved in the acid to thereby produce SnO. ₂ The film is etched. However, it is desirable to use a laser scribing method that can realize simple and low-cost processing.
[0043]
Next, the first semiconductor photoelectric conversion unit 104a and the second semiconductor photoelectric conversion unit 104b are stacked to form the tandem semiconductor photoelectric conversion layer 104.
[0044]
First, the first semiconductor photoelectric conversion unit 104a is formed on the surface electrode layer 102 patterned in the previous step. The first semiconductor photoelectric conversion unit 104a includes a pin junction in which a p-type layer, an i-type layer, and an n-type layer are sequentially stacked (not shown).
[0045]
In addition to the known PECVD method and Cat-CVD method, the present inventors have already disclosed them in Patent Document 3, Japanese Patent Application No. 2001-293031 and Japanese Patent Application No. 2002-38686. Cat-PECVD can be used.
[0046]
Here, for the p-type layer, a hydrogenated amorphous silicon film or a crystalline silicon film containing a microcrystalline silicon phase can be used. The film thickness is adjusted in the range of about 2 to 100 nm depending on the material. 1 × 10 for doping element concentration ¹⁸ ~ 1x10 ²¹ / Cm ³ To the extent, practically p ⁺ A type. SiH used during film formation ₄ , H ₂ And B which is a doping gas ₂ H ₆ In addition to gases such as CH ₄ If a proper amount of gas containing C (carbon) such as _x C _1-x A film is obtained, which is very effective for forming a window layer with little light absorption loss, and also effective for reducing dark current components for improving the open circuit voltage. In addition to C, the same effect can be obtained by mixing an appropriate amount of a gas containing O (oxygen) or a gas containing N (nitrogen).
[0047]
For the i-type layer, which is a photoactive layer, a hydrogenated amorphous silicon film is used and the film thickness is adjusted in the range of about 0.1 to 0.5 μm. In practice, the non-doped film usually shows a slight n-type characteristic. In this case, the non-doped film can be adjusted so as to be substantially i-type by slightly containing a p-type doping element.
[0048]
As the n-type layer, a hydrogenated amorphous silicon film or a crystalline silicon film containing a microcrystalline silicon phase can be used. The film thickness is adjusted in the range of about 2 to 100 nm depending on the material. 1 × 10 for doping element concentration ¹⁸ -10 ²¹ / Cm ³ To the extent, essentially n ⁺ A type. SiH used during film formation ₄ , H ₂ And PH as a doping gas ₃ In addition to gases such as CH ₄ If a proper amount of gas containing C (carbon) such as _x C _1-x A film can be obtained, a film can be formed with little light absorption loss, and it is also effective in reducing dark current components for improving the open circuit voltage. In addition to C, the same effect can be obtained by mixing an appropriate amount of a gas containing O (oxygen) or a gas containing N (nitrogen).
[0049]
In order to further improve the junction characteristics, a substantially i-type non-single-crystal Si layer or non-single-crystal Si is interposed between the p-type layer and the photoactive layer or between the photoactive layer and the n-type layer. _x C _1-x Layers may be inserted. The thickness of the insertion layer at this time is about 0.5 to 50 nm.
[0050]
Here, in order to realize good electrical connection characteristics at the pn reverse junction 108 between the first semiconductor photoelectric conversion unit 104a and the second semiconductor photoelectric conversion unit 104b described below, the first semiconductor photoelectric conversion unit 104a is realized. In the n-type layer included in the conversion unit 104a and the p-type layer included in the second semiconductor photoelectric conversion unit 104b to be described later, it is desirable to increase the crystallization rate at least at a portion where they are in contact with each other. As a result, recombination of majority carriers between both units can be caused with a higher probability, so that the pn reverse junction 108 having more excellent electrical connection characteristics can be realized.
[0051]
Next, a second semiconductor photoelectric conversion unit 104b is formed on the first semiconductor photoelectric conversion unit 104a. The semiconductor photoelectric conversion unit 104b is composed of a pin junction (not shown) in which a p-type layer, an i-type layer, and an n-type layer are sequentially stacked, and thereby, between the n-type layer of the first semiconductor photoelectric conversion unit 104a. In addition, the pn reverse junction 108 can be formed.
[0052]
In addition to the known PECVD method and Cat-CVD method, the present inventors have already disclosed them in Patent Document 3, Japanese Patent Application No. 2001-293031 and Japanese Patent Application No. 2002-38686. The Cat-PECVD method can be used.
[0053]
Here, for the p-type layer, a hydrogenated amorphous silicon film or a crystalline silicon film containing a microcrystalline silicon phase can be used. The film thickness is adjusted in the range of about 2 to 100 nm depending on the material. 1 × 10 for doping element concentration ¹⁸ ~ 110 ²¹ / Cm ³ To the extent, practically p ⁺ A type. SiH used during film formation ₄ , H ₂ And B which is a doping gas ₂ H ₆ In addition to gases such as CH ₄ If a proper amount of gas containing C (carbon) such as _x C _1-x A film is obtained, which is very effective for forming a window layer with little light absorption loss, and also effective for reducing dark current components for improving the open circuit voltage. In addition to C, the same effect can be obtained by mixing an appropriate amount of a gas containing O (oxygen) or a gas containing N (nitrogen).
[0054]
For the i-type layer which is a photoactive layer, a crystalline silicon film typified by a microcrystalline silicon film is used, and the film thickness is adjusted in the range of about 1 to 3 μm. In practice, the non-doped film usually shows a slight n-type characteristic. In this case, the non-doped film can be adjusted so as to be substantially i-type by slightly containing a p-type doping element. At this time, as a film structure, the surface shape after film formation is suitable for optical confinement as an aggregate of columnar crystal grains of (110) plane orientation generated as a result of preferential growth of (110) plane among crystal planes. It is desirable to have a natural concavo-convex structure.
[0055]
As the n-type layer, a hydrogenated amorphous silicon film or a crystalline silicon film containing a microcrystalline silicon phase can be used. The film thickness is adjusted in the range of about 2 to 100 nm depending on the material. 1 × 10 for doping element concentration ¹⁸ -10 ²¹ / Cm ³ To the extent, essentially n ⁺ A type. SiH used during film formation ₄ , H ₂ And PH as a doping gas ₃ In addition to gases such as CH ₄ If a proper amount of gas containing C (carbon) such as _x C _1-x A film can be obtained, a film can be formed with little light absorption loss, and it is also effective in reducing dark current components for improving the open circuit voltage. In addition to C, the same effect can be obtained by mixing an appropriate amount of a gas containing O (oxygen) or a gas containing N (nitrogen).
[0056]
In order to further improve the junction characteristics, a substantially i-type non-single-crystal Si layer may be inserted between the p-type layer and the photoactive layer or between the photoactive layer and the n-type layer. The thickness of the insertion layer at this time is about 0.5 to 50 nm.
[0057]
Next, the semiconductor layer dividing groove 105 is formed. At this time, it is desirable that the semiconductor layer dividing groove 105 is processed and formed by a laser scribing method. As the laser, in order to stop the depth of the through hole with the surface electrode layer 102 exposed, for example, the second harmonic of YAG (wavelength 0.53 μm) is used, and the power is about 0.1 to 0.5 W. Adjust the thickness according to the thickness of the semiconductor photoelectric conversion unit. Thus, the semiconductor photoelectric conversion units 104a and 104b can be removed preferentially and selectively while leaving the surface electrode layer 102. The processing width is about 50 to 100 μm.
[0058]
In addition to the above laser scribing method, the semiconductor layer dividing groove 105 can be formed by a wet etching method using an acidic solution (for example, HF solution and HNO). ₃ (It can be etched with a mixed acid mixed with a liquid), but a resist coating and stripping process is required, and the treatment of the waste liquid acid solution is also expensive, so a laser scribing method that can realize simple and low-cost processing is used. Is preferable.
[0059]
The semiconductor layer dividing groove 105 can fulfill its function as long as the surface electrode layer 102 is exposed. The semiconductor layer dividing groove 105 is not necessarily formed in a continuous groove shape, and may be formed of a plurality of through holes.
[0060]
Next, a metal film is formed as the back electrode layer 106. As this metal film material, it is desirable to use Al (aluminum), Ag (silver), etc., which are excellent in conductive characteristics and light reflection characteristics. As the film forming method, known techniques such as vapor deposition, sputtering, ion plating, and screen printing can be used. At this time, the film thickness is about 0.1 μm or more.
[0061]
The back electrode layer 106 is preferably formed so as to fill the semiconductor layer dividing groove 105 in which the front electrode layer 102 is exposed. According to this, the connection conductor 112 disposed in the semiconductor layer dividing groove 105 is also formed. They can be formed simultaneously.
[0062]
Furthermore, it is more preferable that the back electrode layer 106 has a structure in which a transparent conductive film / metal film are stacked in this order from the side in contact with the semiconductor layer. Thus, by inserting the transparent conductive film between the semiconductor layer and the metal film, it is possible to suppress the phenomenon that the metal film component diffuses into the semiconductor layer and deteriorates the device characteristics. In addition, if an appropriate uneven structure is provided on the surface of the transparent conductive film, light is effectively scattered, so that the light confinement effect effective for improving the efficiency of the solar cell can be enhanced. Here, the transparent conductive film material is SnO as described above. ₂ ITO, ZnO, or the like can be used, and as a film forming method, known techniques such as a CVD method, a vapor deposition method, an ion plating method, a sputtering method, a spray method, and a sol-gel method can be used.
[0063]
Next, a patterning process for forming a back electrode dividing groove 107 is performed on the back electrode layer 106. As a result, the back electrode layer 106 is divided into a plurality of regions corresponding to the power generation region 110 of the photoelectric conversion element. At this time, the back electrode dividing groove 107 is preferably processed and formed by a laser scribing method. The groove depth of the back electrode dividing groove 107 is preferably set to the middle of the semiconductor photoelectric conversion unit 104b so that the pn reverse junction portion 108 is not exposed on the wall surface of the back electrode dividing groove 107. Harmonics (wavelength 0.53 μm) are used, and the power is adjusted in the range of about 0.1 to 0.5 W depending on the thickness of the semiconductor photoelectric conversion unit 104b. By doing so, the back electrode layer 106 can be preferentially removed while leaving a part of the semiconductor photoelectric conversion unit 104b. The processing width is about 50 to 100 μm.
[0064]
Although the basic structure (conventional element structure) of the integrated photoelectric conversion device is formed as described above, the element structure of the present invention is realized by performing laser irradiation described below.
[0065]
That is, the non-power generation region 111 of the integrated photoelectric conversion device obtained up to the above step is locally heated by irradiating laser light from the translucent substrate 101 side, and a highly doped pn reverse junction is obtained. The doping element of the portion 108 is diffused in the vertical direction in the semiconductor layer and dispersed, the doping concentration of the pn reverse junction portion 108 in the laser light irradiation region is reduced, and the doping element profile is changed, so that the lightly doped region 109 is formed. obtain.
[0066]
In this way, the conventional structure has a problem by diffusing and dispersing the doping element present in the pn reverse junction 108 in the vertical direction in the pn reverse junction 108 in the vertical direction of the semiconductor layer, thereby transforming the original highly doped region into the lightly doped region. The lateral leakage of the pn reverse junction 108 can be reduced. This is because the majority carrier density in the lightly doped region 109 is reduced, and a potential barrier is formed between the heavily doped region and a majority carrier flow barrier, so that leakage current hardly flows. Conceivable.
[0067]
Further, the lightly doped region 109 is desirably provided on both sides of the semiconductor dividing groove 105. This is because the lateral leakage current can be suppressed via the pn reverse junction for each of the power generation regions on both sides of the semiconductor dividing groove 105.
[0068]
The doping element concentration in the lightly doped region 109 is desirably at least 1/10 or less of the doping element concentration of the pn reverse junction 108 in the power generation region 110. If the value is larger than this, the effect of increasing the resistance (the effect of reducing the leakage current) hardly appears.
[0069]
In the lightly doped region 109, it is desirable that the p-type doping element and the n-type doping element are in a state of diffusing each other in the partner semiconductor film, thereby reducing the majority carrier density. Becomes even higher. The reason for this is that the effect of lowering the majority carrier density is not only the diffusion of the simple doping element described above, but also the p-type doping element and the n-type doping element acting as opposite conductivity types in the pn reverse junction 108 mutually. It is presumed that this is due to diffusion and offsetting the dope characteristics.
[0070]
In order to control such alteration of the pn reverse junction 108 due to laser light irradiation, it is necessary to optimize the wavelength and irradiation intensity (power) of the laser light. At this time, a wavelength suitable for the absorption characteristics of the semiconductor material is selected as the laser wavelength. When a Si-based film is used as in the present embodiment, for example, the second harmonic of YAG (wavelength 0.53 μm) is used. The power is adjusted by the thickness of the semiconductor photoelectric conversion unit. When Si-based films are stacked in a thickness of about 2 to 3 μm as in this embodiment, the power is set to about 0.1 W or less so that the semiconductor layer is not melted unnecessarily by laser light irradiation. Set conditions. When the semiconductor layer is melted, the impurities are in a substantially uniform distribution state, the junction characteristics of the semiconductor photoelectric conversion units 104a and 104b themselves are destroyed, and the crystal is solidified in a state of a large particle size. This is because there is a problem that it becomes a leak region in the direction.
[0071]
Thus, the integrated photoelectric conversion device of the present invention can be realized.
[0072]
In the above description, the tandem-type thin film Si solar cell including two semiconductor photoelectric conversion units and including one pn reverse junction has been described as an example. However, the present invention is not limited to this, and the object of the present invention is Any form can be used without departing.
[0073]
That is, the present invention can also be applied to a multi-junction photoelectric conversion element including three or more semiconductor photoelectric conversion units and including two or more pn reverse junction portions.
[0074]
Further, the present invention is not limited to Si-based semiconductors, but can be applied to the case where compound-based or organic-based semiconductors are used.
[0075]
In the above description, the case where the manufacturing process of the pn reverse junction by laser irradiation is described at the end of the process is described. However, the process order is not limited to this, and the integrated photoelectric conversion device structure of the present invention is not limited thereto. As long as it is realizable, it can be set as arbitrary process orders. That is, the pn reverse junction portion may be inserted before any step as long as it is a step after a plurality of semiconductor photoelectric conversion units are stacked.
[0076]
【Example】
Examples of the integrated photoelectric conversion device of the present invention are shown below. Table 1 shows a comparison between an integrated photoelectric conversion device to which the present invention is applied and a conventional one. Experimental element, element area = 1 cm ² The number of integrations is 10 and the photoactive layer (Si film) of the semiconductor photoelectric conversion unit is formed under a high-speed film forming condition of 1 nm / s or more, and the lightly doped region 109 of the pn reverse junction 108 is formed. Are formed by laser irradiation. The yield is obtained when a conversion efficiency of 10% or more is counted as a good product.
[0077]
[Table 1]

[0078]
Thus, it can be seen that both the characteristics and the yield are improved by the present invention. This is considered to be because the lateral leakage at the pn reverse junction between the semiconductor photoelectric conversion units can be reduced by the configuration of the present invention.
[0079]
Further, when the doping element concentrations of the pn reverse junction 108 in the power generation region 110 and the lightly doped region 109 were measured by SIMS, one of the pn reverse junction 108 in the power generation region 110 was obtained in the low concentration doped region 109. The best element characteristics and yield were obtained when the ratio was / 10 or less.
[0080]
Further, in the lightly doped region formed by laser irradiation, both p-type doping element B and n-type doping element P are observed, both of which diffuse from one semiconductor layer to the other semiconductor layer. It was found that a concentration gradient was generated. As described above, all of the samples having the low-concentration doped regions in which both doping elements are diffused have good device characteristics and yield.
[0081]
Note that SIMS measurement was performed using O as a primary ion source for B of the doping elements. ²⁺ And for P, Cs is used as the primary ion source. ⁺ Was used. The element concentration was estimated by measuring five different points in the analysis target area and taking the average.
[0082]
【The invention's effect】
According to the integrated photoelectric conversion device of the present invention, , P The majority carrier density causing the lateral leakage in the n-reverse junction can be effectively reduced. As a result, the lateral leakage can be reduced, and high efficiency and high yield can be realized.
[0083]
Furthermore, since the lightly doped region is provided on both sides of the semiconductor dividing groove, the lateral leakage current can be suppressed via the pn reverse junction for each of the power generation regions on both sides of the semiconductor dividing groove. Therefore, the effect of stabilizing the characteristics and obtaining a high yield can be further enhanced.
[0084]
Further, since the doping element concentration in the lightly doped region is 1/10 or less of the doping element concentration in the power generation region, the lateral leakage at the pn reverse junction can be sufficiently reduced.
[0085]
Furthermore, in the lightly doped region, the doping elements contained in the two semiconductor layers having opposite conductivity to each other are diffused in the other semiconductor film, so that these elements are doped with each other. Cancel each other out, the majority carrier density can be extremely effectively reduced, lateral leakage can be reduced, and higher efficiency and higher yield can be obtained.
[0086]
Furthermore, since the lightly doped region is formed by laser irradiation, the structure of the present invention can be easily formed without increasing the complexity of the process and increasing the cost.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a structure of an integrated photoelectric conversion device according to the present invention.
FIG. 2 is a diagram for explaining a structure of a conventional integrated photoelectric conversion device.
FIG. 3 is a diagram for explaining another structure of a conventional integrated photoelectric conversion device.
FIG. 4 is a diagram for explaining another structure of a conventional integrated photoelectric conversion device.
[Explanation of symbols]
101: Translucent substrate
102: Surface electrode layer
103: Front electrode dividing groove
104: Tandem semiconductor photoelectric conversion layer
104a: First semiconductor photoelectric conversion unit
104b: Second semiconductor photoelectric conversion unit
105: Semiconductor layer dividing groove
106: Back electrode layer
107: Back electrode dividing groove
108: pn reverse junction
109: Lightly doped region
110: Power generation area
111: Non-power generation area
112: Connection conductor

Claims (5)

On a transparent substrate, the front electrode layer, a multi-junction semiconductor layer and laminate the back electrode layer were sequentially stacked to form a laminate of the semiconductor photoelectric conversion unit 2 or more having a photoelectric conversion function, in Table electrode layer Dividing into a plurality of power generation regions by a provided surface electrode dividing groove , a semiconductor layer dividing groove provided in the multi-junction semiconductor layer, and a back electrode dividing groove provided in the back electrode layer, and a surface electrode layer of an adjacent power generation region and In the integrated photoelectric conversion device in which the back electrode layer is connected to each other in series by the connection conductor through the semiconductor layer dividing groove,
The dividing grooves provided in each layer are shifted from each other so that the semiconductor layer dividing grooves provided in the multi-junction semiconductor layer are located in a non-power generation region sandwiched between the front electrode dividing grooves and the back electrode dividing grooves. Provided,
The semiconductor photoelectric conversion unit includes a one-conductivity-type semiconductor film and a reverse-conductivity-type semiconductor film, and both adjacent semiconductor photoelectric conversion units form a pn reverse junction where the opposite-conductivity-type semiconductor films are in contact with each other. So
In the non-power generation region, a lightly doped region in which a doping element of the pn reverse junction is diffused in a vertical direction is provided in a part of the pn reverse junction. .   The integrated photoelectric conversion device according to claim 1, wherein the lightly doped region is provided on both sides of the semiconductor dividing groove. The doping element concentration of the lightly doped region, the integrated-type photoelectric conversion device according to claim 1 or 2, characterized in that said less than 1/10 of the doping element concentration of the pn reverse junction portion of the power generation area.   At least two kinds of doping elements contained in a semiconductor film having opposite conductivity types constituting the pn reverse junction are diffused in the semiconductor film in the lightly doped region. The integrated photoelectric conversion device according to claim 1.   5. The integrated photoelectric conversion device according to claim 1, wherein the lightly doped region is formed by laser irradiation.

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