SnO2 surface defects tuned by (NH4)2S for high-efficiency perovskite solar cells

Tin oxide (SnO 2 ) is widely adopted as an electron transport layer (ETL) in perovskite solar cells (PSCs). However, the oxygen vacancies of the SnO 2 not only are the trap states of the nonradiative recombination of photogenerated carriers, but also build the potential barrier of carrier transport. To solve this issue, ammonium sulfide [(NH 4 ) 2 S] is introduced to the SnO 2 precursor for passivating the surface defects by terminating the Sn dangling bonds (S–Sn bonds). After reducing the surface traps, the electron mobility and conductivity of SnO 2 film are enhanced significantly while the carrier recombination is decreased. Additionally, the energy level of S-SnO 2 is also slightly modified. Therefore, this sulfide-passivated mothed remarkably improves the electron collection efficiency of the ETL. Furthermore, the linkage of Sn–S–Pb anchors the perovskite crystals at the perovskite/SnO 2 interface, which increases the electron extraction efficiency and the stability of PSC. Based on this S-SnO 2 ETL, the power conversion efficiency of the PSC is greatly promoted from 18.67% to 20.03%, compared with the reference one. In this study, it is proven that the surface defect passivation of SnO 2 is an efficient and simple method to improve the photovoltaic performance, as a promising ETL for high-efficiency device.