Improvement of Thiourea (Lewis Base)-Modified SnO₂ Electron-Transport Layer for Carbon-Based CsPbIBr₂ Perovskite Solar Cells

In recent years, SnO2 has been widely studied as the electron-transport layer (ETL) of carbon-based CsPbIBr2 perovskite solar cells (PSCs). However, the large lattice mismatch between the SnO2 ETL and the CsPbIBr2 layer and the oxygen vacancy cause nonradiative recombination. Therefore, how to remove the defects between the SnO2 film and the CsPbIBr2 layer is the key to improving the performance. In this paper, thiourea (CH4N2S) is introduced into the SnO2 film as a carrier of S2– (Lewis base), which can capture Pb2+ at the interface between the SnO2 film and the CsPbIBr2 film, so as to reduce the nonradiative recombination between the CsPbIBr2 layer and the ETL and reduce the internal resistance of PSCs. The quality of the perovskite layer is also improved by increasing the size of the crystal, reducing the number of holes, and promoting the transmission ability of the carrier. The results show that the best power conversion efficiency (PCE) obtained by modifying the SnO2 ETL with thiourea (CH4N2S) is 7.18% (41.06% higher than that of the unmodified original PSC). In addition, the PSCs based on the ETL modified by thiourea (CH4N2S) have better stability in the natural environment in contrast to the original PSCs. This paper demonstrated an effective strategy to improve the stability and efficiency of all-inorganic CsPbIBr2 PSCs.