Takahisa Kase

Fabrication of graded band-gap Cu(InGa)Se2 thin-film mini-modules with a Zn(O,S,OH)x buffer layer

Abstract High-performance Cu(InGa)Se2 (CIGS) thin-film absorbers with an intentionally graded band-gap structure have been fabricated by a simple two-stage method using In/CuGa/Mo stacked precursors and H2Se gas. Additional sulfurization step to form a thin Cu(InGa)(SeS)2 surface layer on the absorber is necessary to enhance the grain growth and improve the device performance. Improvement of the interface quality between the absorber and the Zn(O,S,OH)x buffer layer by applying a post-deposition light soaking has, for the first time, resulted in the efficiency of over 14% measured by JQA with a 50 cm2 aperture-area monolithic mini-module. The post-deposition light-soaking treatments would be utilized as an effective tool leading to the accelerated process development with high yield for the future commercial production.

The role of Cu(InGa)(SeS)/sub 2/ surface layer on a graded band-gap Cu(InGa)Se/sub 2/ thin-film solar cell prepared by two-stage method

The purpose of this study is to understand the current baseline process for the absorber formation by a two-stage method and make the process more reliable and reproducible through the investigation of the formation chemistry of the Cu(InGa)Se/sub 2/ (CIGS) thin-film absorbers with a graded band-gap structure and Cu(InGa)(SeS)/sub 2/ (CIGSS) surface layer. A 50-cm/sup 2/ aperture-area efficiency of 13% measured at NREL, which has been reported for the first time in a CIGS thin-film solar module with a Cd-free, sulfur-contained Zn-compound buffer layer, should be a good evidence of the role of CIGSS surface layer on the performance of CIGS thin-film solar cells.

Effects of Cd-free buffer layer for CuInSe/sub 2/ thin-film solar cells

A ZnO buffer layer by a chemical-bath deposition (CBD) method is developed in this study to improve the interface quality between the n-ZnO window layer and p-CuInSe/sub 2/ (CIS) thin-film absorber in CIS thin-film solar cells as one of the approaches to the fabrication of Cd-free thin-film solar cells. The optimization of the fabrication conditions of CBD-ZnO leads to an efficiency of about 10%. These results indicate that the CBD-ZnO buffer layer has a rather high capability to fabricate high-efficiency CIS thin-film solar cells.

Improved FF of CIGS thin-film mini-modules with Zn(O,S,OH)/sub x/ buffer by post-depostion light soaking

In order to explain the observations on the post-deposition light soaking and understand this unique and valuable effect, a model is proposed and confirmed to work well. Based on the model, released H/sub 2/O molecules through the dehydration of Zn(OH)/sub 2/ in the Zn(O,S,OH)/sub x/ buffer during the light soaking is considered as a major player to affect the form factor (FF). The most striking result in this study is the post-deposition light soaking effect can be controlled from reversible to irreversible by adjusting the light soaking conditions. Approach to reduce the Zn(OH)/sub 2/ concentration in the buffer contributes to make a better p-n heterojunction and improve the yield.

High efficiency a-Si:H solar cells by single chamber method

High efficiency hydrogenated amorphous silicon (a-Si:H) solar cells were developed by plasma chemical vapor deposition (P-CVD) using a single chamber. Three techniques to improve the cell efficiency are developed and discussed; (1) obtaining ohmic contact with low resistance at the TCO/p-layer junction employing a-SiO/sub x/ film for TCO/p-layer interface; (2) application of high quality p-type a-SiC:H films by using a two types of doping gas, trimethylboron(TMB) and B/sub 2/H/sub 6/; and (3) zinc oxide (ZnO)/Ag films were used as the back electrode layer. Application of the above three techniques to a single cell of 2.8 cm/sup 2/ size results in the increase of the conversion efficiency above 11.7%.<<ETX>>