Report on industrial attachment on spray coating of buffer layer for CIGS application

Abstract

As one of the mainstream thin film photovoltaic devices, copper indium gallium selenide (CIGS) has significant advantages over other PV competitors. Firstly, CIGS has a high absorption coefficient value of 105/cm2 and a spectral response of 300nm-1300nm, much wider as compared to silicon cells (400-700nm), leading to longer effective time for sun light harvesting everyday. Secondly, CIGS does not have the problem of light-induced degradation, which exists in silicon cells; whereas, it exhibits improving performance over the first few days due to “light-soaking” effect [1]. Thirdly, its flexibility and light weight make it particularly favorable for BIPV and portable power application. Lastly, CIGS solar cell requires less material consumption and simpler fabrication process as compared to silicon solar cells.

Currently the highest efficiency CIGS solar cell is achieved with CBD-CdS buffer layer (eff: 19.2%) [2]. However, due to its environmental toxicity and low band gap, there is a motivation to look for Cd-free material for buffer layer [3].

In this study, deposition using ultrasonic spray pyrolysis method, In2S3 buffer layer has been optimized by varying the precursor ratio, etching condition, substrate temperature and annealing condition etc. In addition, a new buffer layer concept based on ZnS dots/In2S3 bi-layer structure will be evaluated. ZnS nanodots are believed to passivate the buffer/absorber interface, hence reduce the interface recombination, as demonstrated by HZB using Spray ILGAR method. For further enhancing the conductivity & band gap of In2S3, tin (Sn) has been doped into In2S3 for examination. The outcome of this work provides overview of optimizing various factors that affect the performance of CIGS solar cell with In2S3 buffer layer.