High Efficiency CuInS_2 Thin Film Solar Cells

点击翻译按钮获取中文摘要

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.