JP2005136333A - Concentrating solar cell and method for manufacturing compound semiconductor solar cell including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concentrating solar cell having high photoelectric conversion rate, and to provide a method for manufacturing a compound semiconductor solar cell which effectively utilizes spaces. <P>SOLUTION: The concentrating solar cell 13 comprises an upper solar cell including an emitter layer made of AlInGaP or InGaP and a window layer formed on the emitter layer, an intermediate solar cell including an emitter layer made of InGaAs or GaAs, and a lower solar cell made of Ge, in this order starting from the side of a light-receiving surface. The concentrating solar cell 13 has an arrangement wherein the thickness of the emitter layer in the upper solar cell is 0.1μm or smaller, the sheet resistance of the emitter layer and the window layer altogether in the upper solar cell is 200 Ω/SQUARE or smaller, and the distance between grid electrodes set up on the side of the light-receiving surface is 0.15mm or smaller. The method for manufacturing the compound semiconductor solar cell 14, including a step of forming the concentrating solar cell 13 and a non-concentrating solar cell 12, is also provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a concentrating solar cell and a method for producing a compound semiconductor solar cell including the same, and particularly relates to a concentrating solar cell having high photoelectric conversion efficiency and a method for producing a compound semiconductor solar cell including the same.

  In recent years, an example of using a multi-junction type compound semiconductor solar cell using a III-V group compound semiconductor such as GaAs as a space solar cell used for a power source of space equipment such as an artificial satellite is increasing. This multi-junction compound semiconductor solar cell can be expected to have a higher photoelectric conversion efficiency than a Si solar cell that has been widely used as a space solar cell. Suitable for use on small satellites and high power satellites.

  Among these, the solar cell having the highest photoelectric conversion efficiency at present is not limited to terrestrial use or space use, for example, is a three-junction type compound semiconductor solar cell having an InGaP / InGaAs / Ge structure. This compound semiconductor solar cell receives, for example, an upper solar cell including a window layer made of AlInP and an emitter layer made of InGaP, an intermediate solar cell including an emitter layer made of InGaAs, and a lower solar cell made of Ge. Includes in this order from the face side. The thickness of the emitter layer of the upper solar cell of this compound semiconductor solar cell is 0.1 μm or less, the sheet resistance of the combined layer of the window layer and the emitter layer of the upper solar cell is 200Ω / □ or less, and the light receiving surface When the interval between the grid electrodes installed on the side is about 1 mm, a photoelectric conversion efficiency exceeding 30% is achieved at the time of non-condensing (see Non-Patent Documents 2 and 3).

  Conventionally, a concentrating solar cell has been manufactured by reducing the area of the light receiving surface of the non-condensing solar cell having high photoelectric conversion efficiency when not condensing. However, when high-intensity light collected on this concentrating solar cell is incident, the photocurrent increases, the reduction of the fill factor (FF) due to series resistance occurs, and the photoelectric conversion efficiency is greatly reduced. There was a problem.

Further, this non-condensing solar cell has already been put into practical use as a space solar cell. As shown in the schematic top view of FIG. 9, the space solar cell includes two rectangular non-concentrating solar cells 12 of about 40 mm × 70 mm in the entire space solar cell 100 having a diameter of 100 mm. What is being used. However, in this space solar cell, there is a problem that the non-condensing solar cell 12 occupies a small proportion of the size of the space solar cell as a whole, so that the space cannot be effectively used.
T.Takamoto, T.Agui et al, “MULTIJUNCTION SOLAR CELL TECHNOLOGIES-HIGH EFFICIENCY, RADIATION RESISTANCE, AND CONCENTRATOR APPLICATIONS”. T. Takamoto, et al, “Over 30% Efficient InGaP / GaAs tandem solar cells”, Appl. Phys. Lett. 70, p. 381 (1997). T. Takamoto, T. Agui et al, “High Efficiency InGaP / InGaAs tandem Solar Cells on Ge Substrates”, Proceeding of the 28th PVSC, p.976 (2000).

  An object of the present invention is to provide a concentrating solar cell having high photoelectric conversion efficiency. Moreover, the objective of this invention is providing the manufacturing method of the compound semiconductor solar cell which utilized space effectively.

  The present invention relates to an upper solar cell including an emitter layer made of AlInGaP or InGaP and a window layer formed on the emitter layer, an intermediate solar cell including an emitter layer made of InGaAs or GaAs, and a lower solar cell made of Ge. And in this order from the light receiving surface side, the thickness of the emitter layer of the upper solar cell is 0.1 μm or less, and the emitter layer and the window layer of the upper solar cell are combined This is a concentrating solar cell in which the sheet resistance of the layer is 200 Ω / □ or less, and the interval between the grid electrodes installed on the light receiving surface side is 0.15 mm or less.

Here, the area of the light receiving surface of the concentrating solar cell of the present invention is preferably 50 mm ² or less.

  Furthermore, the present invention is a method for producing a compound semiconductor solar cell including the concentrating solar cell, wherein a step of forming a semiconductor layer above a semiconductor substrate, and a concentrating device on a part above the semiconductor layer are provided. It is the manufacturing method of a compound semiconductor solar cell including the process of installing and forming a concentrating solar cell and a non-condensing solar cell.

  Moreover, in the manufacturing method of the compound semiconductor solar cell of this invention, it is preferable that the semiconductor layer which comprises a concentrating solar cell and the semiconductor layer which comprises a non-condensing solar cell are formed in the same process. .

In the compound semiconductor solar cell manufacturing method of the present invention, the area of the light receiving surface of the concentrating solar cell is 50 mm ² or less, and the area of the light receiving surface of the non-condensing solar cell is 100 mm ² or more. It is preferable.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where the same structure as the non-condensing type solar cell to which photoelectric conversion efficiency falls at the time of condensing is used, the concentrating type solar cell which has high photoelectric conversion efficiency can be provided. . Moreover, according to this invention, the manufacturing method of the compound semiconductor solar cell which utilized space effectively can be provided.

  Embodiments of the present invention will be described below. In the drawings of the present application, the same reference numerals denote the same or corresponding parts.

  The present invention relates to an upper solar cell including an emitter layer made of AlInGaP or InGaP and a window layer formed on the emitter layer, an intermediate solar cell including an emitter layer made of InGaAs or GaAs, and a lower solar cell made of Ge. Are arranged in this order from the light receiving surface side, and the thickness of the emitter layer of the upper solar cell is 0.1 μm or less, and the layer of the emitter layer and the window layer of the upper solar cell is combined. This is a concentrating solar cell having a sheet resistance of 200Ω / □ or less and an interval between grid electrodes formed on the light receiving surface side of 0.15 mm or less.

  This is because the thickness of the emitter layer of the upper solar cell of the non-concentrating solar cell having the structure of InGaP / InGaAs / Ge that achieves the above-described photoelectric conversion efficiency exceeding 30% is set to 0.1 μm or less. The grid electrode formed on the light receiving surface side while adopting the conventional technical idea that the sheet resistance of the combined emitter layer and window layer of the battery is 200Ω / □ or less (see Non-Patent Documents 2 and 3). The present inventors have found that a particularly high photoelectric conversion efficiency can be obtained by setting the distance of 0.15 mm or less. Here, as shown in the schematic top view of FIG. 1, the interval between the grid electrodes is a grid electrode intersecting with the electrode pad portion 10 in the surface electrode 11 installed on the light receiving surface side of the concentrating solar cell of the present invention. This is an interval X of 8. Moreover, since AlInGaP has a larger band gap than InGaP, it is preferable in that AlInGaP can be further improved by using AlInGaP as a material constituting the emitter layer of the upper solar cell. Similarly, since GaAs has a larger band gap than InGaAs, it is preferable in that photoelectric conversion efficiency can be further improved by using GaAs as a material constituting the emitter layer of the intermediate solar cell.

The area of the light receiving surface of the concentrating solar cell of the present invention is preferably 50 mm ² or less, more preferably 16 mm ² or less, and further preferably 1 mm ² or less. This is because the photocurrent generated in the concentrating solar cell of the present invention decreases (the current density does not change) as the area of the light receiving surface decreases, so that the voltage drop due to series resistance decreases, and the fill factor (FF ) Becomes larger.

  In the present invention, as shown in the schematic top view of FIG. 2, the smaller the area of the light receiving surface in the space other than the space occupied by the non-condensing solar cell 12 in the compound semiconductor solar cell 14, The concentrating solar cell 13 of the present invention having high conversion efficiency can be formed. As a result, it is possible not only to effectively utilize a space that could not be effectively utilized in the past, but also to output the compound semiconductor solar cell 14 including the non-concentrating solar cell 12 and the concentrating solar cell 13. Can also be improved.

  Here, in the present invention, it is preferable that the non-concentrating solar cell 12 and the concentrating solar cell 13 are manufactured by the same process. That is, when the materials and structures constituting the non-condensing solar cell 12 and the concentrating solar cell 13 are the same, the non-condensing solar cell 12 and the concentrating solar cell 13 (such as a Fresnel lens) The manufacturing cost of the compound semiconductor solar cell 14 can be reduced because the same process can be simultaneously formed using the same process. Furthermore, this compound semiconductor solar cell 14 is comprised from the non-condensing solar cell 12 which has high photoelectric conversion efficiency at the time of non-condensing, and the concentrating solar cell 13 which has high photoelectric conversion efficiency at the time of condensing. Therefore, it is possible to obtain high output by converting incident solar energy into electric energy with high efficiency.

Further, the area of the light receiving surface of the non-concentrating solar cell 12 is preferably larger than the area of the light receiving surface of the concentrating solar cell 13 described above, and particularly preferably 100 mm ² or more. When the area of the light receiving surface of the non-condensing solar cell 12 is 100 mm ² or more, the photoelectric conversion efficiency of the non-condensing solar cell 12 is increased by increasing the light receiving area with respect to the area of the electrode pad portion. This is because it tends to improve.

  FIG. 3 shows a schematic cross-sectional view of a preferred example of a compound semiconductor solar cell comprising the concentrating solar cell and the non-condensing solar cell of the present invention. This compound semiconductor solar cell includes a buffer layer 2, which is an n-type GaAs layer having a thickness of 300 μm, on a lower solar cell 1 composed of a p-type Ge layer 1a having a thickness of 150 μm and an n-type Ge layer 1b having a thickness of 1 μm. Tunnel junction layer 3 composed of an n-type InGaP layer 3a having a thickness of 0.02 μm and a p-type AlGaAs layer 3b having a thickness of 0.02 μm, a back surface field layer 4a which is a p-type InGaP layer having a thickness of 0.1 μm, and a thickness An intermediate solar cell comprising a base layer 4b which is a 3 μm p-type GaAs layer, an emitter layer 4c which is an n-type GaAs layer having a thickness of 0.1 μm, and a window layer 4d which is an n-type AlInP layer having a thickness of 0.03 μm. 4, a tunnel junction layer 5 composed of an n-type InGaP layer 5a having a thickness of 0.02 μm and a p-type AlGaAs layer 5b having a thickness of 0.02 μm, a back surface electric field layer 6a which is a p-type AlInP layer having a thickness of 0.03 μm, 4μ thickness An upper solar cell 6 comprising a base layer 6b which is a p-type AlInGaP layer, an emitter layer 6c which is an n-type AlInGaP layer having a thickness of 0.05 μm, and a window layer 6d which is an n-type AlInP layer having a thickness of 0.03 μm; A semiconductor layer 9 in which a cap layer 7 made of an n-type GaAs layer is formed in this order is formed. Then, the grid electrode 8 is formed on the semiconductor layer 9. Here, the sheet resistance of the layer including the emitter layer 6c and the window layer 6d of the upper solar cell 6 is 200Ω / □ or less.

  Sunlight incident on the compound semiconductor solar cell is absorbed in the upper solar cell 6, the intermediate solar cell 4 and the lower solar cell 1 in order from light having a short wavelength (high energy), and is generated by this solar light. The carriers thus separated are separated at the junction of the emitter layer and the base layer, collected by the grid electrode 8, and taken out to the outside. Here, the window layer is formed on the emitter layer in order to suppress disappearance of carriers generated by sunlight due to recombination with surface defects of the emitter layer. The back surface electric field layer is formed below the base layer in order to suppress recombination between the surface defects of the base layer and the carriers by generating an internal electric field. Further, the tunnel junction layer uses a tunnel current to improve the connection between the upper solar cell 6 and the intermediate solar cell 4 and between the intermediate solar cell 4 and the lower solar cell 1. Is provided. The cap layer is provided to reduce current loss due to series resistance such as electrode contact resistance.

In FIG. 4, the flowchart of a preferable example of the manufacturing method of this compound semiconductor solar cell is shown. First, in step 1 (S1), an MOCVD method (metal organic vapor phase epitaxy) is used to form FIG. 3 on a 110 mm diameter Ga-doped p-type Ge substrate (Ga concentration: 5.0 × 10 ¹⁸ cm ⁻³ ). The semiconductor layer 9 shown in FIG. When the semiconductor layer 9 is formed, the n-type dopant is diffused from the n-type GaAs layer on the p-type Ge substrate to form a pn junction in the Ge substrate, and the lower solar cell 1 is formed.

Here, the formation of the semiconductor layer 9 is performed in a state where a p-type Ge substrate is placed in the MOCVD apparatus and the temperature in the MOCVD apparatus is set to 700 ° C., for example. The GaAs layer is formed by introducing TMG (trimethyl gallium) and AsH ₃ (arsine) into the MOCVD apparatus. The InGaP layer is formed by introducing TMI (trimethylindium), PH ₃ (phosphine), and TMG. The AlGaAs layer is formed by introducing TMAl (trimethylaluminum), TMG, and AsH ₃ . The AlInP layer is formed by introducing TMAl, TMI, and PH ₃ . The AlInGaP layer is formed by introducing TMAl, TMI, TMG, and PH ₃ . Further, SiH ₄ (monosilane) is further introduced into the MOCVD apparatus for the formation of the n-type semiconductor layer, and DEZn (diethyl zinc) is further introduced for the formation of the p-type semiconductor layer. Note that CBr ₄ (carbon tetrabromide) is introduced in place of DEZn for forming the p-type AlGaAs layers constituting the tunnel junction layers 3 and 5.

  Next, in step 2 (S 2), a surface electrode including the grid electrode 8 is formed on the cap layer 7. The surface electrode is formed by first forming a resist pattern in which holes are formed in the shape of the surface electrode on the cap layer 7 by a photolithography method, and then setting the surface electrode in a vacuum vapor deposition apparatus to be made of Au containing 12% Ge. A layer (thickness: 100 nm) is formed by a resistance heating method, and a Ni layer (thickness: 20 nm) and an Au layer (thickness: 5000 nm) are successively formed by an EB vapor deposition method (electron beam vapor deposition method). Then, the resist is removed by lift-off to form a surface electrode.

  Next, in step 3 (S3), using the surface electrode as a mask, the portion of the cap layer 7 where the surface electrode is not formed is removed using an alkaline aqueous solution.

  Subsequently, in step 4 (S4), a resist pattern in which holes are formed in the shape to be mesa-etched by photolithography is formed, and the semiconductor layer in the portion where the holes are formed is mesa-etched using an alkaline aqueous solution and an acid solution. Then, a part of the surface of the lower solar cell 1 is exposed.

In step 5 (S5), a back electrode made of an Ag layer (thickness: 1000 nm) is formed on the back surface of the lower solar cell 1 by EB vapor deposition. Then, a TiO ₂ layer (thickness: 50 nm) and an Al ₂ O ₃ layer (thickness: 85 nm) are sequentially formed as an antireflection film on the exposed surface of the lower solar cell 1 by EB vapor deposition.

  Thereafter, in step 6 (S6), a heat treatment at, for example, 380 ° C. is performed in a nitrogen atmosphere, both for the sintering of the front electrode and the annealing of the back electrode and the antireflection film.

  Finally, in step 7 (S7), the semiconductor layer 9 is cut so that the dicing line enters the mesa-etched line, and a light condensing device such as a Fresnel lens is installed above the semiconductor layer 9. Thus, the compound semiconductor solar cell 14 shown in FIG. 2 is manufactured. Here, as the compound semiconductor solar cell 14, two rectangular non-condensing solar cells 12 of 40 mm × 70 mm (no concentrating device is installed) and a rectangular concentrating solar cell 13 of 7 mm × 9 mm ( 38 pieces of light collecting devices are installed).

  FIG. 5 shows current-voltage characteristics of the non-condensing solar cell 12. Here, the open circuit voltage (Voc) of the non-condensing solar cell 12 was 2.567 V, the short circuit current (Isc) was 0.476 A, and the FF was 0.872. Moreover, the photoelectric conversion efficiency (Eff) of the non-condensing solar cell 12 was 28.2%. In addition, the current-voltage characteristic of the non-condensing solar cell 12 was measured using a solar simulator that irradiates AM0 reference sunlight.

FIG. 6 shows changes in FF when the area of the light receiving surface of the concentrating solar cell 13 is changed. For example, the FF of the concentrating solar cell 13 when concentrating 500 times (500 sun) is about 0.86 when the area of the light receiving surface of the concentrating solar cell 13 is 100 mm ² , and 49 mm ^2. When it is, it is about 0.876, which is greatly improved. Further, the FF was further improved as the area of the light receiving surface of the concentrating solar cell 13 was reduced to 16 mm ² (FF: about 0.885) and 1 mm ² (FF: about 0.892).

  In FIG. 7, the change of FF when the space | interval of the grid electrode of the concentrating solar cell 13 is changed is shown. Here, the condensing magnification is 250 times. The FF of the concentrating solar cell 13 at the time of 250 times condensing was about 0.845 when the distance between the grid electrodes was 0.15 mm. Note that the FF did not change much even when the interval between the grid electrodes was made narrower than 0.15 mm.

FIG. 8 shows a change in Eff with respect to a change in the focusing magnification when the area of the light receiving surface of the concentrating solar cell 13 is 50 mm ² and the grid electrode interval is 0.12 mm. As shown in FIG. 8, when normal sunlight was condensed 100 to 500 times, Eff was 36% or more, and very high photoelectric conversion efficiency was obtained.

  In addition, the said characteristic evaluation of the concentrating solar cell 13 was performed by condensing the light of the solar simulator which irradiates AM1.5G standard sunlight with a Fresnel lens.

  In this application, the GaAs layer refers to a layer containing Ga and As. The InGaP layer refers to a layer containing In, Ga, and P. An AlGaAs layer is a layer containing Al, Ga, and As. An AlInP layer refers to a layer containing Al, In, and P. An AlInGaP layer is a layer containing Al, In, Ga, and P.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  According to the present invention, a concentrating solar cell having high photoelectric conversion efficiency can be provided, and a concentrating solar cell and a non-condensing solar cell having high photoelectric conversion efficiency that effectively utilize space. Since the manufacturing method of the compound semiconductor solar cell which consists of these can be provided, this invention can be utilized suitably for the solar cell field | area.

It is a typical enlarged top view of a preferable example of the surface electrode of the concentrating solar cell of this invention. It is a typical top view of a preferable example of the compound semiconductor solar battery of the present invention. It is typical sectional drawing of a preferable example of the compound semiconductor solar cell of this invention. It is the flowchart which showed a preferable example of the manufacturing method of the compound semiconductor solar cell of this invention. It is the figure which showed the current-voltage characteristic of the non-condensing type solar cell used for this invention. It is the figure which showed the change of FF when changing the area of the light-receiving surface of the concentrating solar cell of this invention. It is the figure which showed the change of FF when the space | interval of the grid electrode of the concentrating solar cell of this invention is changed. It is the figure which showed the change of Eff with respect to the change of the condensing magnification of the concentrating solar cell of this invention. It is a typical top view of an example of the conventional solar cell for space.

Explanation of symbols

  1 lower solar cell, 1a p-type Ge layer, 1b n-type Ge layer, 2 buffer layer, 3,5 tunnel junction layer, 3a, 5a n-type InGaP layer, 3b, 5b p-type AlGaAs layer, 4 middle solar cell, 4a, 6a Back surface electric field layer, 4b, 6b Base layer, 4c, 6c Emitter layer, 4d, 6d Window layer, 6 Upper solar cell, 7 Cap layer, 8 Grid electrode, 9 Semiconductor layer, 10 Electrode pad part, 11 Surface electrode , 12 Non-condensing solar cell, 13 Concentrating solar cell, 14 Compound semiconductor solar cell, 100 Space solar cell.

Claims (5)

  An upper solar cell including an emitter layer made of AlInGaP or InGaP and a window layer formed on the emitter layer; an intermediate solar cell including an emitter layer made of InGaAs or GaAs; and a lower solar cell made of Ge. A concentrating solar cell including in this order from the light-receiving surface side, the emitter layer of the upper solar cell having a thickness of 0.1 μm or less, and a layer combining the emitter layer and the window layer of the upper solar cell The concentrating solar cell is characterized in that the sheet resistance is 200Ω / □ or less and the interval between the grid electrodes installed on the light receiving surface side is 0.15 mm or less. 2. The concentrating solar cell according to claim 1, wherein an area of a light receiving surface of the concentrating solar cell is 50 mm ² or less.   A method of manufacturing a compound semiconductor solar cell including the concentrating solar cell according to claim 1, wherein a step of forming a semiconductor layer above a semiconductor substrate, and a concentrating device on a part above the semiconductor layer The manufacturing method of a compound semiconductor solar cell including the process of installing and forming the said concentrating solar cell and a non-condensing solar cell.   4. The compound semiconductor solar cell according to claim 3, wherein the semiconductor layer constituting the concentrating solar cell and the semiconductor layer constituting the non-condensing solar cell are formed by the same process. Manufacturing method. The area of the light receiving surface of the concentrating solar cell is 50 mm ² or less, and the area of the light receiving surface of the non-condensing solar cell is 100 mm ² or more. A method for producing a compound semiconductor solar cell.

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