Research On Deposition ZnS Buffer Layer By Chemical Solution Methods

CIGS-based thin film solar cells gain a increasing concern nowadays, for their high performance and relative low costs. And the standard device structure of CIGS-based solar cells includes a very thin chemical-bath-deposition (CBD) CdS buffer layer between the CIGS absorber layer and the transparent front electrode, the CBD-CdS buffer layer plays a determined role in the improvement of cell efficiency. But Cd is toxic and hazardous to environment, even worse, CdS has a narrow transmittance spectral regin of 550 nm-800nm. So several efforts to substitute the CdS layer by other nontoxic low-absorbing materials have been made, and CBD-ZnS has been considered as the best alternative. However, CBD method itself has many defects which are hard to change, and SILAR process are based on CBD, it can compensate the CBD's faults. In this article, we hope to confirm that SILAR process is better than CBD method in preparing ZnS buffer layer by comparison.We prepared ZnS thin films by CBD and SILAR respectively, and optimized the process parameters. After analysis, we made conclusions as follows:a. The as-deposited films made by CBD and SILAR both are amorphous, and the films are still amorphous when they were annealed in air below 400℃, if the anneal tempreture reaches 500℃, the films will change into ZnO polycrystalline.b. Both films have similar chemical components, but CBD films have higher oxygen content than SILAR films; SILAR films have a better stoichiometric proportion than CBD films.c. SILAR films are denser and uniformer than CBD films, and also have higher transmittance. Control of SILAR process is easier than CBD.d. Ultra-sonic rinsing can improve the growth velocity of SILAR films significantly.According to the researches on ZnS buffer layer, the density and transmittance of the films will determine the cell's capability, crystallinity and stoichiometric proportion are not dominant reasons. Hence, we assume that SILAR method is more proper than CBD method in fabricating ZnS buffer layer.