Compound solar cell

Abstract

A compound solar battery according to the present invention is provided with a laminated film (2) including: a reflection layer (20) formed of an AlGaAs layer; a front surface-side light absorption layer (10) formed between a surface electrode (1) and the reflection layer (20); and a back surface-side light absorption layer (30) formed between the reflection layer (20) and a substrate (3). The reflection layer (20) is formed of a front surface-side reflection layer (20u) and a back surface-side reflection layer (20d). The Al content ratio in the front surface-side reflection layer (20u) is set to be greater than that in the back surface-side reflection layer (20d). The back surface-side light absorption layer (30) is formed by laminating, from the substrate (3) side, a first InGaP layer (31), a first GaAs layer (32), a second InGaP layer (33), a second GaAs layer (34), and a third InGaP layer (35). The thickness of the second GaAs layer (34) is set to be larger than that of the first GaAs layer (32).

Description

Technical Field

[0001] The present invention relates to compound solar cells.

Background Art

[0002] In the case of currently mainstream crystalline silicon solar cells, the theoretical maximum energy conversion efficiency is about 29%, but the products on the market are about 15%. On the other hand, research and development of next-generation solar cells that can exceed the efficiency of single-junction solar cells and reduce costs using new concepts and materials not on the conventional extension line is accelerating. Among solar cells, compound solar cells have an efficiency of 37.9% (a value confirmed by the National Institute of Advanced Industrial Science and Technology in February 2013 (cell area: about 1 cm 2 )), and various solar cell structures that can raise the conversion efficiency limit have been actively proposed and demonstrated around the world. The current world's highest efficiency is 46% for a four-junction solar cell in experimental results. On the other hand, Professor Takashi Kita of the Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, and Research Assistant Shigeo Asahi et al. have proposed highly efficient power generation by multiple excitons as a never-before-seen solar cell structure (quantum dots). In addition, development is also underway to absorb the spectral components of sunlight with long wavelengths that were transmitted and lost in conventional cells and theoretically raise the conversion efficiency to 50% or more. In such a development situation, the actual products that are sufficient for general use are compound solar cells with a triple junction of about 36% for use in space and are expected to be applied to the automotive industry in the future. Note that Patent Document 1 proposes a compound solar cell.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a compound solar cell, it is desired to be able to utilize light in a wide wavelength range and further increase the power generation efficiency.

[0005] Therefore, an object of the present invention is to provide a compound solar cell that can effectively utilize light in a wide wavelength range.

Means for Solving the Problems

[0006] The compound solar cell of the present invention according to claim 1 is a compound solar cell in which a front electrode 1, a stacked film 2, a substrate 3, and a back electrode 4 are stacked in this order, and power generation is performed by making light incident from the side of the partially formed front electrode 1. As the stacked film 2, it has a reflective layer 20 made of an AlGaAs layer, a front-side light absorption layer 10 formed between the front electrode 1 and the reflective layer 20, and a back-side light absorption layer 30 formed between the reflective layer 20 and the substrate 3. The reflective layer 20 is formed of a front-side reflective layer 20u and a back-side reflective layer 20d, the Al content ratio of the front-side reflective layer 20u is made larger than that of the back-side reflective layer 20d, and the back-side light absorption layer 30 is formed by stacking a first InGaP layer 31, a first GaAs layer 32, a second InGaP layer 33, a second GaAs layer 34, and a third InGaP layer 35 from the side of the substrate 3, and the film thickness of the second GaAs layer 34 is made thicker than that of the first GaAs layer 32. The present invention according to claim 2 is the compound solar cell according to claim 1, wherein the front-side light absorption layer 10 sandwiches an InGaP layer 13 between a first AlInP layer 12 and a second AlInP layer 14, and the ratio of Al in the first AlInP layer 12 laminated on the side of the reflective layer 20 is made larger than that of the second AlInP layer 14 laminated on the side of the front electrode 1. The present invention according to claim 3 is characterized in that in the compound solar cell according to claim 2, the InGaP layer 11 is sandwiched between the front surface side reflection layer 20u and the first AlInP layer 12.

Advantages of the Invention

[0007] According to the present invention, light in a wide wavelength range can be effectively utilized.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0009] The compound solar cell according to the first embodiment of the present invention has, as a laminated film, a reflection layer made of an AlGaAs layer, a front surface side light absorption layer formed between the front surface electrode and the reflection layer, and a back surface side light absorption layer formed between the reflection layer and the substrate. The reflection layer is formed by a front surface side reflection layer and a back surface side reflection layer, the Al content ratio of the front surface side reflection layer is made larger than that of the back surface side reflection layer, and the back surface side light absorption layer is formed by laminating a first InGaP layer, a first GaAs layer, a second InGaP layer, a second GaAs layer, and a third InGaP layer from the substrate side, and the film thickness of the second GaAs layer is made thicker than that of the first GaAs layer. According to this embodiment, the laminated film laminates the front surface side light absorption layer, the reflection layer, and the back surface side light absorption layer. The reflection layer is formed by the front surface side reflection layer and the back surface side reflection layer, and the Al content ratio of the front surface side reflection layer is made larger than that of the back surface side reflection layer, so that light is easily reflected and the light can be confined in the GaAs layer. By making the film thickness of the second GaAs layer forming the back surface side light absorption layer thicker than that of the first GaAs layer, the energy confined in the quantum well in the layer in contact with InGaP can be made almost the same.

[0010] The second embodiment of the present invention is a compound solar cell according to the first embodiment, wherein the surface-side light absorption layer sandwiches an InGaP layer between a first AlInP layer and a second AlInP layer and is laminated on the reflection layer side. The ratio of Al in the first AlInP layer laminated on the surface electrode side is made larger than that of the second AlInP layer laminated on the surface electrode side. According to this embodiment, light energy can be easily stored in the InGaP layer. And.

[0011] The third embodiment of the present invention is a compound solar cell according to the second embodiment, wherein the InGaP layer is sandwiched between the surface-side reflection layer and the first AlInP layer. According to this embodiment, light energy can be further stored.

Example

[0012] Hereinafter, a compound solar cell according to an embodiment of the present invention will be described. FIG. 1 is an enlarged cross-sectional photograph of a main part of the compound solar cell according to this example. In the compound solar cell according to this example, a surface electrode 1, a laminated film 2, a substrate 3, and a back surface electrode 4 are laminated in this order, and power generation is performed by making light incident from the surface electrode 1 side where it is partially formed. In the compound solar cell according to this example, a laminated film 2 is formed on the surface of a substrate 3 made of Ge, and a surface electrode 1 is partially formed on the laminated film 2. A protective film 5a made of TiOx is formed on the surface of the laminated film 2 where the surface electrode 1 is not formed, and a protective film 5b made of AlOx is further formed. A back surface electrode 4 is formed on the back surface of the substrate 3.

[0013] FIG. 2 is an enlarged cross-sectional photograph of a main part obtained by further enlarging a part of FIG. 1. In this example, the surface electrode 1 is formed by laminating an Ag layer and an Au / Pt layer. The Ag layer is on the outer surface, and a TiOx layer 6 and a GaAs layer 7 are laminated in this order on the lower surface of the Au / Pt layer. The laminated film 2 is formed under the GaAs layer 7.

[0014] The laminated film 2 laminates a front-side light absorption layer 10, a reflection layer 20, and a back-side light absorption layer 30. The reflection layer 20 is composed of an AlGaAs layer. The reflection layer 20 is formed by a front-side reflection layer 20u and a back-side reflection layer 20d. The front-side reflection layer 20u is composed of a composition ratio of Al being 0.5 - 0.8 and Ga being 0.2 - 0.5, with a thickness of 50 - 100 nm. The back-side reflection layer 20d is composed of a composition ratio of Al being 0.1 - 0.4 and Ga being 0.6 - 0.9, with a thickness of 10 - 65 nm, preferably 40 - 65 nm. In this way, the Al content ratio of the front-side reflection layer 20u is made higher than that of the back-side reflection layer 20d. Also, the thickness of the front-side reflection layer 20u is made thicker than that of the back-side reflection layer 20d. It is preferable that the Al content ratio of the front-side reflection layer 20u is about 4 times that of the back-side reflection layer 20d, and the thickness of the front-side reflection layer 20u is about 2 times that of the back-side reflection layer 20d.

[0015] Both the front-side reflection layer 20u and the back-side reflection layer 20d are AlGaAs layers that constitute an electromagnetic wave reflection layer, and both have the function of reflecting electromagnetic waves. The front-side reflection layer 20u and the back-side reflection layer 20d each have the role of a reflection layer, but in order to reflect more electromagnetic waves, two layers with different refractive indexes are combined. The reflection layer 20 forms a Bragg mirror by making the Al content ratio of the front-side reflection layer 20u higher than that of the back-side reflection layer 20d and reflects light (electromagnetic waves). In this way, by reflecting light with the reflection layer 20, the light is confined in the GaAs layers 32 and 34, and it is easier to absorb wavelengths of 700 nm or more. The amount of electric power in the double-decker type layer is more than that in the double heterostructure. Thereby, absorption of near-infrared light up to around 900 nm can be enabled. Power generation up to 930 nm was confirmed in the test. In the back-side light absorption layer 30 where the GaAs layers 32 and 34 and the InGaP layers 31, 33, and 35 are laminated, the amount of energy absorbed is increased by the reflection layer 20 made of an AlGaAs layer.

[0016] The backside light absorption layer 30 is formed between the reflective layer 20 and the substrate 3. The backside light absorption layer 30 is formed by laminating, from the substrate 3 side, a first InGaP layer 31, a first GaAs layer 32, a second InGaP layer 33, a second GaAs layer 34, and a third InGaP layer 35. The film thickness of the second GaAs layer 34 is made thicker than that of the first GaAs layer 32. The film thickness of the first InGaP layer 31 is made thinner than those of the second InGaP layer 33 and the third InGaP layer 35. The film thickness of the second InGaP layer 33 is made thicker than those of the first InGaP layer 31 and the third InGaP layer 35. The second GaAs layer 34 is doped with secondary ions to form an emitter layer and a base layer. The first GaAs layer 32 is doped with secondary ions in the same manner as the second GaAs layer 34 to form an emitter layer , a tunnel layer, and a base layer. This second GaAs layer 34 and the first GaAs layer 32 are sandwiched by the third InGaP layer 35, the second InGaP layer 33, and the first InGaP layer 31. Therefore, a heterojunction is formed by stacking layers having pn junctions. In this way, a self-formed quantum dot InGaP layer is formed on top of the pn-bonded GaAs layer. Since different compounds are laminated, it can be called a heterojunction, and due to the quantum tunneling effect, current flows without waste.

[0017] ​The backside light absorption layer 30 has a double-decker type heterojunction by sandwiching a first GaAs layer 32 having a bandgap of 1.43 between a first InGaP layer 31 and a second InGaP layer 33 having a high bandgap (1.88), and sandwiching a second GaAs layer 34 having a bandgap of 1.43 between the second InGaP layer 33 and a third InGaP layer 35 having a high bandgap (1.88). Thereby, an energy wall "hetero-barrier" is formed, and energy can be confined to the first GaAs layer 32 and the second GaAs layer 34 having a small energy bandgap, and it is considered that incident light energy can be absorbed without waste.

[0018] By making the film thickness of the second GaAs layer 34 on the incident light side thicker than that of the first GaAs layer 32 on the substrate 3 side, the energy confined in the quantum wells in the InGaP layers 31, 33, 35 can be made almost the same. Therefore, the energies in the quantum wells that conserve energy resonate with each other, increasing the resonant tunneling. As a result, the power generated near the incident light side can also be extracted without waste. Also, by making the GaAs layers 32, 34 into multiple layers and making the film thickness of the second GaAs layer 34 on the incident light side thicker than that of the first GaAs layer 32 on the substrate 3 side, not only visible light but also far-infrared light near the substrate 3 can be taken into the GaAs layers 32, 34, securing more power.

[0019] The front side light absorption layer 10 sandwiches an InGaP layer 13 between a first AlInP layer 12 and a second AlInP layer 14, and the ratio of Al in the first AlInP layer 12 laminated on the reflection layer 20 side is higher than that of the second AlInP layer 14 laminated on the surface electrode 1 side. The surface-side light absorption layer 10 sandwiches an InGaP layer 13 between a first AlInP layer 12 and a second AlInP layer 14 having a high bandgap (2.10) and forms a heterojunction. The Al ratio of the second AlInP layer 14 is set to 40 or more so that light energy remains in the GaAs layers 32 and 34, and light is not absorbed by the first AlInP layer 12 and the second AlInP layer 14. The first AlInP layer 12 has an Al ratio of 45, which is higher than the Al ratio of the second AlInP layer 14, making it easier to store light energy in the InGaP layer 13. The energy of the InGaP layer 13 in a single junction is 1.86 eV (electron volts), and since the energy from the InGaP layer 13 sandwiched between the first AlInP layer 12 and the second AlInP layer 14 has two quantum wells, it is considered to be 4.00 eV or more to be. An InGaP layer 11 is formed between the surface-side reflective layer 20u and the first AlInP layer 12. That is, this InGaP layer 11 is sandwiched between the surface-side reflective layer 20u and the first AlInP layer 12. By configuring the surface-side light absorption layer 10 in this way, it becomes possible to absorb ultraviolet light up to around 250 nm, and power generation up to 230 nm was confirmed. The stacked film 2 is composed of compounds so that the stacked crystal constants are substantially the same layers, and does not have a buffer layer for aligning the crystal constants.

[0020] As a compound solar cell according to this embodiment, when a module with a size of 5 mm x 5 mm and a thickness of 1.6 mm was used for confirmation, power generation from 230 nm to 930 nm was confirmed, and a generated power of 1.6 V to 2.4 V could be obtained. Also, a stable wavelength could be confirmed in the temperature range from 20°C to 80°C.

Industrial Applicability

[0021] The compound solar cell of the present invention can perform power generation using not only sunlight but also indoor lighting.

Explanation of Reference Numerals

[0022] 1 Surface electrode 2 Stacked film 3 Substrate 4 Back electrode 5a Protective film 5b Protective film 6 TiOx layer 7 GaAs layer 10 Surface-side light absorption layer 11 InGaP layer 12 First AlInP layer 13 InGaP layer 14 Second AlInP layer 20 Reflective layer 20d Back-side reflective layer 20u Surface-side reflective layer 30 Back-side light absorption layer 31 First InGaP layer 32 First GaAs layer 33 Second InGaP layer 34 Second GaAs layer 35 Third InGaP layer

Claims

1. A compound solar cell in which a front electrode, a laminated film, a substrate, and a back electrode are laminated in this order, and which generates electricity by illuminating light from the partially formed front electrode side, As the laminated film, a reflective layer made of an AlGaAs layer; a front-side light absorbing layer formed between the front electrode and the reflective layer; a backside light absorbing layer formed between the reflective layer and the substrate; having The reflective layer is formed of a front-side reflective layer and a back-side reflective layer, The Al content ratio of the front-side reflective layer is made higher than that of the back-side reflective layer, The backside light absorbing layer is forming a first InGaP layer, a first GaAs layer, a second InGaP layer, a second GaAs layer, and a third InGaP layer in a stacked manner from the substrate side; The second GaAs layer is thicker than the first GaAs layer. A compound solar cell.

2. the front-side light absorbing layer has an InGaP layer sandwiched between a first AlInP layer and a second AlInP layer; The ratio of Al in the first AlInP layer laminated on the reflective layer side is set to be equal to that in the first AlInP layer laminated on the front electrode side. The second AlInP layer is thicker than the first AlInP layer.

2. The compound solar cell according to claim 1 .

3. An InGaP layer is sandwiched between the front-side reflective layer and the first AlInP layer.

3. The compound solar cell according to claim 2 .

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