Abstract
uIn1-XGaXSe2 (CIGS) thin-film solar cell is considered to be one of the most promising material in the future of the solar industry due to its high performance and low-cost commercial production. The CIGS thin film solar cells deposited on the flexible substrate to offer a new type of solar cell applications. In this study, we developed a one-step sputtering process by co-sputtering quaternary target and Ga2Se3 binary target without extra selenium supply on the stainless steel flexible substrate. This kind of process will be scaled up by roll-to-roll deposition process to reduce the production cost significantly. To reach highly efficient solar cells on the stainless steel flexible substrate，deposition of diffusion barrier is needed to suppress iron diffusion form substrate into CIGS absorber layer . If iron diffuses into the CIGS absorber layer, it will create a deep-defect in the CIGS absorber layer and detriment to efficiency. We deposited 1um Chromium (Cr) acts as a diffusion barrier to block iron from stainless steel substrate and improve the roughness of stainless steel substrate. In order to solve stainless steel substrate without extra sodium form substrate, we sputter sodium fluoride target to supply sodium source before depositing CIGS absorber layer. The fabrication of CIGS thin film is made by co-sputtering quaternary target and Ga2Se3 binary target in one-step sputtering process. Usage of Ga2Se3 binary target will create normal Ga-grading profile during the deposition which help carriers be collected. We will discuss the impact of sodium content of the CIGS thin film for the electrical property, Ga-grading profile, structural characteristics and device performance. The conversion efficiency can achieve 9.15% at 600℃.However, higher working temperature will make Se element loss in the CIGS thin films, which limit the device performance. From PL analysis, with Se supply in annealing process can remove Se-like defect transition and enhance film quality. By adjusting the temperature to reduce selenium deficiency, the conversion efficiency can be improved from 9.15% to 11.25% at 550℃without extra Se supply.