Siam Physics Congress 2015

Influence of thickness reduction for CGS/CIS/CGS absorber layer on solar cell performance

20 May 2015, 14:00

3h 30m

Board: SUR-03

Poster presentation Surface, Interface and Thin Film Poster-1

Speaker

Ms Busarin Noikaew (Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok, THAILAND 10330)

Description

Typical $\rm CuIn_{1-x}Ga_xSe_2$ (CIGS) thin film solar cells on soda-lime glass (SLG) substrates consist of six different layers of thin film materials, i.e. SLG/Mo/CIGS/CdS/i-ZnO/ZnO(Al)/Al-grids. One of the commonly used deposition techniques for the CIGS thin films is the three-stage deposition process. However, the deposition of CIS/CGS bilayers and CGS/CIS/CGS trilayers were employed for the fabrication of CIGS thin film solar cells in order to reduce the materials and times used in the process and induce the non-uniformity of In and Ga due to their different diffusivities that could lead to band gap grading. The substrate temperature was kept constant at 560°C throughout the deposition. The typical thickness of the CIGS was approximately 1.8 μm. The thickness reduction of CGS/CIS/CGS layers was investigated from 1.8 μm down to 0.5 μm. The efficiencies of the devices fabricated from the CIS/CGS and CGS/CIS/CGS layers, both with 1.8 μm thick, showed the maximum value of 12.8 % and 15.5%, respectively. The thickness reduction showed slightly loss in the short-circuit current and the open-circuit voltage resulting in the reduction of the device efficiencies. For example, when the thickness is approximately reduced by 55%, the device efficiency is decreased by 15%. The external quantum efficiency measurements were performed to compare the spectral response of the devices. The cross sectional SEM images of the CIGS devices are shown and compared for their corresponding efficiencies. In addition, XRD and EDS were used to indicate and investigate the non-uniformity distribution of In and Ga in the CIGS absorber layers.