Multifunctional Thiophene-Based Interfacial Passivating Layer for High-Performance Perovskite Solar Cells

The performance improvement of perovskite solar cells (PSCs) is strongly limited by the defects generated at the carrier transport layers/perovskite interface. Due to the complexity of intrinsic defects occurring in both SnO2 and perovskite layers, the introduction of appropriate multifunctional passivating molecules or groups is of great interest to suppress the defects at the interface of SnO2/perovskite. In this work, a facile way to simultaneously passivate the defects at both the surface of SnO2 and the bottom surface of the perovskite layer has been proposed using an interlayer of 3-chlorothiophene-2-carboxylic acid (TCA-Cl). Carboxylic acid in TCA-Cl can form a chemical linker between SnO2 and perovskite via an esterification, leading to the reduction of surface hydroxyl group defects of SnO2. The S, −COO–, and −Cl can modulate the surface electronic states of SnO2 and strengthen the binding at the interface of SnO2/perovskite, and moreover, they passivate the iodine vacancies (VI+) and undercoordinated Pb2+ defects on the surface of perovskite films. Besides, the energy-level alignment is very well modulated by the strong binder of TCA-Cl, leading to the improved carrier extraction at the interface of SnO2/perovskite. As a result, the conversion efficiency of MAPbI3 PSCs achieves up to 21.07% (18.41% for the control), with decreased hysteresis and increased stability.