Comparison of ZnS Film Growth on Glass and CIGS Substrates via Hydrazine-assisted Chemical Bath Deposition for Solar Cell Application

We investigate the effect of hydrazine on the growth and physical characteristics of ZnS thin films deposited on both soda-lime glass (SLG) and copper indium gallium selenide (CIGS)/Mo/SLG substrates as a function of the relative molar ratio of hydrazine to ammonia reagent, r(c), for various deposition times t(d). As rc is varied from 0 to 0.56, all the ZnS films on SLG (thickness of d similar to 38 nm) with hydrazine exhibit an amorphous structure, [S/Zn] composition of similar to 0.65, and direct energy bandgap of E-g = 3.54 - 3.75 eV. To compare the difference in device quality corresponding to the two types of substrates, we fabricate CIGS solar cells using ZnS buffers grown under conditions of r(c) = 0.28, 0.42 for t(d) = 30 min, 15 min and without hydrazine with r(c) = 0.0 and t(d) = 90 min. The sample obtained with the ZnS buffer under conditions of r(c) = 0.28, t(d) = 30 min exhibits the best solar cell performance of eta = 12.03 %. Our results prove that using hydrazine for ZnS buffer layer preparation via chemical bath deposition can significantly enhance the film quality for CIGS solar-cell fabrication.