2001 Fiscal Year Final Research Report Summary
High Efficiency CuInS_2 Thin Film Solar Cells
| Project/Area Number |
11450137
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
電子デバイス・機器工学
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| Research Institution | Shinshu University |
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Principal Investigator |
ITO Kentaro Shinshu University, Department of Electrical and Electronic Engineering, Professor, 工学部, 教授 (20020977)
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| Co-Investigator(Kenkyū-buntansha) |
HASHIMOTO Yoshio Shinshu University, Department of Electrical and Electronic Engineering, Associate Professor, 工学部, 助教授 (30262687)
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| Project Period (FY) |
1999 – 2001
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| Keywords | solar cell / compound semiconductor / thin film |
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| Research Abstract |
A 12.25 % efficiency solar cell has been achieved using the CuInS_2 thin film as an optical absorber layer produced by a sequential process that is advantageous to mass production of large area cells. Here we added a small amount of Ga to a metallic precursor and then sulfurized it by rapid thermal process to obtain a flat absorber layer with good crystallinity.
The diode factor and the dark current density of a heterojunction was decreased by using a composite buffer layer which consists of a very thin Zn compound layer sandwiched between a CdS buffer layer and an absorber layer. The efficiency of the cell was thus improved to 12.1 %.
In the heterojunction consisting of chemical bath deposited Zn( S, O, OH ) and In( S, O, OH ) thin buffer layer instead of toxic CdS, we observed conduction band offsets of 0.4 eV ( energy cliff ) and 0.8 eV ( energy spike ), respectively. The solar cell with the former ( latter ) heterojunction exhibited a 7 % ( 10.1 % ) efficiency. In the former ( latter ) case, we needed annealing of the heterojunction ( surface treatment of the absorber surface by an iodide solution ).
The various characteristics of the thin film solar cell such as capacitance-voltage curve, current-voltage curve and spectral photoresponse could be explained by a theretical device model, where we assume the existence of a thin n-type CulnS_2 layer at the heterointerface. The experimental finding that the open-circuit voltage increases with decreasing the electric field at the junction agreed fairly well with the theoretical expectation.
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