Abstract
CIGS solar cells have drawn a lot of attention in solar cells field. In order to improve the process, the development of Cd-free alternative buffer has been one of important objectives from viewpoint of environmental issues and short-wavelength adsorption. Nowadays, the most high efficiency Cd-free CIGS solar cell is zinc sulfide fabricated by chemical bath deposition. The thin film is usually made of ZnS, ZnO and Zn(OH)2 during chemical reaction. However, on the account of the presence of Zn(OH)2 phase and low bonding energy ZnS, it leads to poor cell performance attributed in low fill factor and shows distorted J-V curve. The cell performance can be enhanced by continuously illuminated for minutes to hours, which has been found by many groups called light soaking effect. In the first part of the thesis, we carried out chemical etching and compared the differences of two chemical processes to improve the formation of ZnS phase and ease the presence of Zn(OH)2, which could achieve 10.67% of efficiency with light soaking treatment. In the second part, we analyzed the dynamic variant of J-V characteristics and electrical properties for ZnS(O,OH)-buffer CIGS solar cell when light soaking treatment. The efficiency can get its saturation within 30 minutes light soaking treatment. Moreover, the ex-situ and in-situ X-ray photoelectron spectroscopy measurement revealed the reversible and irreversible model of light soaking effect. In order to shorten the light soaking treatment time, we furthered to propose an ammonia-free process which could get 10.01 % with slight light soaking effect.