Tin–Selenium Secondary Phase Etching of Cu2ZnSnSe4: A Selective Removal Route To Improve Solar Cell Efficiency

In this study, we removed type II Sn–Se secondary phases from Cu 2 ZnSnSe 4 (CZTSe) absorber surface via selective chemical etching and then examined the influence of this etching on the performances of solar cell devices. Experiment results indicate that the morphology of Sn–Se secondary phases are determined by the Ar gas flow rate (Sn/Se ratio) of the selenization process in the CZTSe absorber layer. Round or semicircular structures (type II) of Sn–Se secondary phases formed in films with a higher Ar gas flow rate (Sn/Se ratio) selenization process. We found that HNO 3 with 3 HCl could remove type II Sn–Se secondary phases, thereby improving average device efficiency from 3.8% to 5.6%.