Enhanced Performance of Planar Perovskite Solar Cells Using Thioacetamide-Treated SnS₂ Electron Transporting Layer Based on Molecular Ink

Improving the electro-optical properties of the electron transport layers (ETLs) is considered one of the most promising solutions to increase the efficiency of the perovskite solar cells (PSCs). In this study, we focused on the spin-coated tin­(IV) sulfide (SnS₂) as the ETL with two different sulfur sources, thiourea (TU) and thioacetamide (TAA) (SnS₂(TU) and SnS₂(TAA)), and investigated the effects of surface passivation of the prepared ETL with TU and TAA (SnS₂-TU and SnS₂-TAA). The treatment is shown to be useful in reducing the surface roughness of the SnS₂ ETL and to passivate the interfacial trap states at the ETL/perovskite interface, leading to better contact between them. Among the prepared samples, the SnS₂(TU) led to a smoother ETL rather than SnS₂(TAA). Finally, the best results of the produced PSCs were related to the samples with SnS₂(TU) and passivated with TAA (SnS₂(TU)-TAA) in which the power conversion efficiency (PCE) promoted from 11.98% in the case of SnS₂(TU) ETL to 15.14% in SnS₂(TU)-TAA ETL with a 37% increase in power conversion efficiency (PCE). As an important role, TAA treatment could compensate the sulfur vacancy which was proved by XPS tests. Moreover, the SnS₂(TU)-TAA ETL increased the long-term stability of the device without any encapsulation under ambient conditions, retaining 86% of the initial PCE after 30 days, while the device with the SnS₂(TU) ETL could maintain about 64% of the original PCE.