Defect Control Strategy by Bifunctional Thioacetamide at Low Temperature for Highly Efficient Planar Perovskite Solar Cells

Titania (TiO2) has wide applications in the realm of perovskite solar cells (PSCs). Because high-temperature processing severely limits the application of flexible and tandem devices, it is significant to develop a high-quality electron-transport layer (ETL) by low-temperature processing. Here, we design a new strategy by introducing a bifunctional molecule (thioacetamide, TAA) in the TiO2 ETL. During the low-temperature annealing, the N and S atoms in TAA can bond with the Ti atom in the ETL and the Pb atom in the perovskite (PVK) layer, respectively. The formation of coordinate bonds is beneficial to increase the crystallinity and reduce the roughness of TiO2 ETLs and PVK layers, which effectively passivate the defects. Meanwhile, the energy level matching between the ETL and PVK is optimized. The structure characterization and electrochemical measurement demonstrate the design. Compared with precursor doping, surface spin-coating is a more effective method for introducing TAA into TiO2. Significantly, the PSC based on the surface spin-coated TAA TiO2 ETL achieves the best power conversion efficiency (PCE) of 21.17%. Nevertheless, the PSC fabricated with the pristine TiO2 ETL offers a PCE of 19.52% under the same conditions. The results demonstrate a novel method for optimizing the properties of PSCs.