(NH4)2S-induced improvement of CdS buffer layer for 15.52% efficiency solution-processed CIGS solar cell

Heterojunction interfacial engineering plays a crucial role for the CIGS efficiency promotion. Chemical bath deposition (CBD) prepared CdS is the most preferred buffer for CIGS solar cells. Hence, manipulating the CdS properties to further boost heterojunction quality is a promising way to achieve higher efficiency CIGS solar cells. In this work, CdS buffer layer was modified by (NH 4 ) 2 S (AS-treatment) solutions. The results showed that after AS treatment, the impurities on CdS film were cleaned and the S vacancy was passivated. Moreover, it introduced larger build-in electric field, wider depletion width and less interface defect densities, which contributed to suppressed interface recombination and more efficient carrier separation and collection. Consequently, the CIGS solar cell based on AS-treatment achieved champion efficiency of 15.52%, with improved V OC of 643 mV and FF of 73.3%.