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

Tin oxide (SnO2) is widely adopted as an electron transport layer (ETL) in perovskite solar cells (PSCs). However, the oxygen vacancies of the SnO2 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 [(NH4)(2)S] is introduced to the SnO2 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 SnO2 film are enhanced significantly while the carrier recombination is decreased. Additionally, the energy level of S-SnO2 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/SnO2 interface, which increases the electron extraction efficiency and the stability of PSC. Based on this S-SnO2 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 SnO2 is an efficient and simple method to improve the photovoltaic performance, as a promising ETL for high-efficiency device.