Compound solar cell

Abstract

A compound solar cell according to the present invention has, as a laminated film (2), a reflective layer (20) comprising an AlGaAs layer; a surface-side light-absorbing layer (10) formed between the surface electrode (1) and the reflective layer (20); and a rear surface-side light absorption layer (30) formed between the reflection layer (20) and the substrate (3), the reflection layer (20) is formed by a front surface-side reflection layer (20u) and a rear surface-side reflection layer (20d), the Al content ratio of the front surface-side reflection layer (20u) is greater than that of the rear surface-side reflection layer (20d), the rear surface-side light absorption layer (30) is formed by laminating 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 substrate side (3), and the second GaAs layer (34) is thicker than the first GaAs layer (32).

Description

Technical Field

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

[0002] Regarding the energy conversion efficiency of solar cells, the theoretical maximum value for currently mainstream crystalline silicon solar cells is approximately 29%, but the current circulating products are around 15%.

[0003] On the other hand, the research and development of the next generation of solar cells is accelerating: using new concepts and materials that are not on the same line as before, the efficiency of single-junction solar cells is expected to exceed that of single-junction solar cells, and at a lower cost. Among solar cells, the efficiency of compound solar cells is 37.9% (the value confirmed by the National Institute of Advanced Industrial Science and Technology in February 2013 (cell area: about 1cm 2 Since then, the world has been working to propose and demonstrate various solar cell structures that can push the limits of conversion efficiency. Experimental results show that the world's highest efficiency currently stands at 46% for a quad-junction solar cell. Meanwhile, a research team led by Professor Kita Takashi and Assistant Professor Asahi Shigeo of the Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, has proposed a high-efficiency power generation based on multiple excitons, an unprecedented solar cell structure (quantum dot). Furthermore, development is underway to absorb spectral components of sunlight with longer wavelengths that are lost in conventional cells, theoretically increasing conversion efficiency to over 50%. With this development, compound solar cells that achieve a 36% efficiency for triple-junction solar cells are now being used in space, and are expected to be applied in the automotive industry and other fields.

[0004] Furthermore, Patent Document 1 proposes a compound solar cell.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 4804571 Summary of the Invention

[0008] In compound solar cells, it is desired to utilize light in a wide wavelength range and further improve power generation efficiency.

[0009] Therefore, an object of the present invention is to provide a compound solar cell capable of effectively utilizing light in a wide wavelength range.

[0010] The compound solar cell of the present invention described in claim 1 is a compound solar cell, which is stacked in sequence on a surface electrode 1, a stacked film 2, a substrate 3 and a back electrode 4, and generates electricity by allowing light to enter from the side of the partially formed surface electrode 1. It is characterized in that the stacked film 2 has a reflective layer 20 including an AlGaAs layer; a surface-side light absorption layer 10 formed between the surface 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 by a surface-side reflective layer 20u and a back-side reflective layer 20d, the Al content ratio of the surface-side reflective layer 20u is higher than that of the back-side reflective layer 20d, and the back-side light absorption layer 30 is stacked from the substrate 3 side to form 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, and the film thickness of the second GaAs layer 34 is thicker than that of the first GaAs layer 32.

[0011] The present invention described in claim 2 is a compound solar cell according to claim 1, characterized in that the surface-side light absorption layer 10 uses a first AlInP layer 12 and a second AlInP layer 14 to sandwich an InGaP layer 13, so that the proportion of Al in the first AlInP layer 12 stacked on the side of the reflective layer 20 is greater than that in the second AlInP layer 14 stacked on the side of the surface electrode 1.

[0012] The present invention described in claim 3 is the compound solar cell according to claim 2 , characterized in that the InGaP layer 11 is sandwiched between the front-side reflective layer 20 u and the first AlInP layer 12 .

[0013] According to the present invention, light in a wide wavelength range can be effectively utilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FIG1 is an enlarged cross-sectional photograph of a main part of a compound solar cell according to one embodiment of the present invention.

[0015] Figure 2 It will Figure 1 A further enlarged cross-sectional photograph of a portion of the main portion.

[0016] (Explanation of Symbols)

[0017] 1: Surface electrode; 2: Laminated 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: 1st AlInP layer; 13: InGaP layer; 14: 2nd AlInP layer; 20: Reflection layer; 20d: Back-side reflection layer; 20u: Surface-side reflection layer; 30: Back-side light absorption layer; 31: 1st InGaP layer; 32: 1st GaAs layer; 33: 2nd InGaP layer; 34: 2nd GaAs layer; 35: 3rd InGaP layer. DETAILED DESCRIPTION

[0018] The compound solar cell of the first embodiment of the present invention has, as a stacked film,: a reflective layer including an AlGaAs layer; a surface-side light absorption layer formed between a surface electrode and the reflective layer; and a back-side light absorption layer formed between the reflective layer and a substrate. The reflective layer is formed by the surface-side reflective layer and the back-side reflective layer, so that the Al content ratio of the surface-side reflective layer is higher than that of the back-side reflective layer. The back-side light absorption layer is stacked from the substrate side to form a first InGaP layer, a first GaAs layer, a second InGaP layer, a second GaAs layer and a third InGaP layer, so that the film thickness of the second GaAs layer is thicker than the first GaAs layer. According to this embodiment, the stacked film comprises a surface-side light absorption layer, a reflective layer, and a back-side light absorption layer. The reflective layer is formed by the surface-side reflective layer and the back-side reflective layer. The Al content ratio of the surface-side reflective layer is made higher than that of the back-side reflective layer. Therefore, light is easily reflected and can be sealed in the GaAs layer. By making the thickness of the second GaAs layer forming the back-side light absorption layer thicker than the first GaAs layer, the energy sealed in the quantum wells in the layers respectively connected to InGaP can be made approximately the same.

[0019] A second embodiment of the present invention is a compound solar cell according to the first embodiment, wherein the surface-side light absorption layer comprises an InGaP layer sandwiched between a first AlInP layer and a second AlInP layer, and wherein the first AlInP layer stacked on the reflective layer side has a higher Al content than the second AlInP layer stacked on the surface electrode side. According to this embodiment, light energy can be easily accumulated in the InGaP layer.

[0020] A third embodiment of the present invention is the compound solar cell according to the second embodiment, wherein the InGaP layer is sandwiched between the front-side reflective layer and the first AlInP layer. According to this embodiment, light energy can be further accumulated.

[0021] Example

[0022] Hereinafter, a compound solar cell according to an embodiment of the present invention will be described.

[0023] Figure 1 This is an enlarged cross-sectional photograph of a main part of the compound solar cell according to this embodiment.

[0024] In the compound solar cell of this embodiment, a surface electrode 1, a laminated film 2, a substrate 3, and a back electrode 4 are stacked in this order, and power generation is performed by incident light from the partially formed surface electrode 1 side.

[0025] The compound solar cell of this embodiment has a laminated film 2 formed on the surface of a substrate 3 comprising Ge, and a surface electrode 1 formed on a portion of the laminated film 2. On the surface of the laminated film 2 where the surface electrode 1 is not formed, a protective film 5a comprising TiOx and a protective film 5b comprising AlOx are formed.

[0026] A back electrode 4 is formed on the back surface of the substrate 3 .

[0027] Figure 2 It will Figure 1 A further enlarged cross-sectional photograph of a portion of the main portion.

[0028] In this embodiment, the surface electrode 1 is a stack of an Ag layer and an Au / Pt layer, with the Ag layer as the outer surface, and a TiOx layer 6 and a GaAs layer 7 stacked in this order on the lower surface of the Au / Pt layer.

[0029] The stacked film 2 is formed below the GaAs layer 7 .

[0030] The laminated film 2 is formed by laminating a front-side light-absorbing layer 10 , a reflecting layer 20 , and a back-side light-absorbing layer 30 .

[0031] The reflective layer 20 is composed of an AlGaAs layer.

[0032] The reflective layer 20 is formed of a front-side reflective layer 20u and a back-side reflective layer 20d.

[0033] The front side reflective layer 20u has a composition ratio of Al to Ga of 0.5-0.8 and a thickness of 50-100 nm. The back side reflective layer 20d has a composition ratio of Al to Ga of 0.6-0.9 and a thickness of 10-65 nm, preferably 40-65 nm.

[0034] Thus, the Al content of the front-side reflective layer 20u is higher than that of the back-side reflective layer 20d. Furthermore, the thickness of the front-side reflective layer 20u is greater than that of the back-side reflective layer 20d. The Al content of the front-side reflective layer 20u is approximately four times that of the back-side reflective layer 20d, and preferably, the thickness of the front-side reflective layer 20u is approximately twice that of the back-side reflective layer 20d.

[0035] The front-side reflective layer 20u and the back-side reflective layer 20d are AlGaAs layers that form electromagnetic wave reflection layers, and both have the function of reflecting electromagnetic waves. The front-side reflective layer 20u and the back-side reflective layer 20d each function as a reflective layer, but in order to reflect more electromagnetic waves, the two layers with different refractive indices are combined.

[0036] The reflective layer 20 has a higher Al content in the front-side reflective layer 20u than in the back-side reflective layer 20d, forming a Bragg mirror to reflect light (electromagnetic waves). By using the reflective layer 20 to reflect light, it is easier to trap light in the GaAs layers 32 and 34, absorbing wavelengths above 700nm. The amount of power in the double-layer structure is greater than that of a double heterostructure. This allows for absorption of near-infrared light up to around 900nm. Experiments have confirmed power generation up to 930nm.

[0037] In the back surface side light absorption layer 30 in which the GaAs layers 32 and 34 and the InGaP layers 31 , 33 , and 35 are stacked, the amount of energy absorbed by the reflective layer 20 including the AlGaAs layer increases.

[0038] The back-side light-absorbing layer 30 is formed between the reflective layer 20 and the substrate 3 .

[0039] 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 substrate 3 side. The second GaAs layer 34 is thicker than the first GaAs layer 32. The first InGaP layer 31 is thinner than the second InGaP layer 33 and the third InGaP layer 35. The second InGaP layer 33 is thicker than the first InGaP layer 31 and the third InGaP layer 35.

[0040] 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.

[0041] The second GaAs layer 34 and the first GaAs layer 32 are sandwiched between the third InGaP layer 35, the second InGaP layer 33, and the first InGaP layer 31. Thus, a heterojunction is formed by stacking layers having pn layers.

[0042] Thus, an InGaP layer of self-generated quantum dots is formed on top of the GaAs layer forming the pn junction. The stacking of different compounds creates a heterojunction, allowing current to flow without waste due to the quantum tunneling effect.

[0043] The backside light absorption layer 30 comprises a first GaAs layer 32 with a band gap of 1.43° sandwiched between a first InGaP layer 31 and a second InGaP layer 33, both with a high band gap of 1.88°. Furthermore, a second GaAs layer 34 with a band gap of 1.43° is sandwiched between a second InGaP layer 33, also with a high band gap of 1.88°, and a third InGaP layer 35, forming a double-layer heterojunction. This is believed to create an energy barrier, a "heterobarrier," which traps energy within the first and second GaAs layers 32 and 34, both with smaller energy band gaps, allowing for efficient absorption of incident light energy.

[0044] By making the film thickness of the second GaAs layer 34 on the light-entering side thicker than the first GaAs layer 32 on the substrate 3 side, the energy sealed in the quantum wells of the InGaP layers 31, 33, and 35 can be made roughly the same. Therefore, the energies in the quantum wells that store energy resonate with each other, increasing the resonance tunnel. As a result, the power generated at a position close to the light-entering side can be extracted without waste. In addition, by making the GaAs layers 32 and 34 multilayer and making the film thickness of the second GaAs layer 34 on the light-entering side thicker than the first GaAs layer 32 on the substrate 3 side, not only visible light can be introduced into the GaAs layers 32 and 34, but also far-infrared light close to the substrate 3 can be introduced into the GaAs layers 32 and 34, which can ensure more power.

[0045] The surface-side light absorbing layer 10 includes an InGaP layer 13 sandwiched between a first AlInP layer 12 and a second AlInP layer 14 . The first AlInP layer 12 stacked on the reflective layer 20 side has a higher Al content than the second AlInP layer 14 stacked on the surface electrode 1 side.

[0046] The surface-side light absorption layer 10 comprises an InGaP layer 13 sandwiched between a first AlInP layer 12 and a second AlInP layer 14, each with a high band gap (2.10), forming a heterojunction. The Al ratio in the second AlInP layer 14 is set to 40 or greater, allowing light energy to remain within the GaAs layers 32 and 34 while preventing light absorption by the first AlInP layer 12 and the second AlInP layer 14. The Al ratio in the first AlInP layer 12 is set to 45, which is higher than the Al ratio in the second AlInP layer 14, thereby facilitating the accumulation of light energy within the InGaP layer 13. The energy of the InGaP layer 13 in a single junction is 1.86 eV (electron volts). Since the energy from the InGaP layer 13 sandwiched between the first AlInP layer 12 and the second AlInP layer 14 forms two quantum wells, it is considered to be 4.00 eV or greater.

[0047] In addition, the InGaP layer 11 is formed between the front-side reflective layer 20 u and the first AlInP layer 12 . That is, the InGaP layer 11 is sandwiched between the front-side reflective layer 20 u and the first AlInP layer 12 .

[0048] By configuring the front-side light-absorbing layer 10 in this manner, absorption of ultraviolet light up to approximately 250 nm was achieved, and power generation up to 230 nm was confirmed.

[0049] The laminated film 2 is composed of compounds so as to form laminated layers having substantially the same crystal constants, and does not include a buffer layer for making the crystal constants uniform.

[0050] The compound solar cell of this example was tested using a module measuring 5mm x 5mm and 1.6mm thick. It was confirmed that power generation from 230nm to 930nm was possible, with a power output of 1.6V to 2.4V. Furthermore, a stable wavelength was observed within a temperature range of 20°C to 80°C.

[0051] The compound solar cell of the present invention can generate electricity not only by utilizing sunlight but also by utilizing indoor lighting.

Claims

1. A compound solar cell comprising a surface electrode, a laminated film, a substrate, and a back electrode stacked in this order, wherein power generation is performed by allowing light to enter from the partially formed surface electrode side, characterized in that: The laminated film has: a reflective layer comprising an AlGaAs layer; a surface-side light-absorbing layer formed between the surface electrode and the reflective layer; and a back-side light absorbing layer formed between the reflective layer and the substrate, The reflective layer is formed by 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 back side light absorption layer is formed by stacking 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. The second GaAs layer is thicker than the first GaAs layer.

2. The compound solar cell according to claim 1, characterized in that The surface side light absorption layer is formed by sandwiching an InGaP layer between a first AlInP layer and a second AlInP layer. The ratio of Al in the first AlInP layer stacked on the reflective layer side is set to be higher than that in the second AlInP layer stacked on the surface electrode side.

3. The compound solar cell according to claim 2, characterized in that The InGaP layer is sandwiched between the surface-side reflective layer and the first AlInP layer.

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