Small Molecule Modulator at the Interface for Efficient Perovskite Solar Cells with High Short‐Circuit Current Density and Hysteresis Free

Interface engineering is widely applied in the one‐step antisolvent deposition for elevating efficiency of the perovskite solar cells (PSCs). Herein, an alcohol‐soluble small molecule, namely 2‐mercaptoimidazole (MI), is inserted between the hole transport layer and perovskite layer to form a cross‐linking bridge, which is built through: i) Coulomb interaction between the negatively charged MI and positively charged poly (3,4‐ethylene dioxythiophene); ii) electrostatic interaction between imidazolium cation and iodide anion in perovskite. The cross‐linking bridge can accelerate the hole transmission and inhibit interfacial recombination. Hence, by the optimum design of MI concentration, hysteresis‐free devices with a high power conversion efficiency of 20.68% are obtained. The overall efficiency increase is due to significantly enhanced short‐circuit current density from 21.28 to 23.45 mA cm−2 and slightly raised open‐circuit voltage from 1.06 to 1.08 V, suggesting that the MI modified layer can effectively improve the performance of the devices. Moreover, unencapsulated devices with MI interfacial modification show better environmental stability compared to the reference devices. This facile interfacial approach is promising for future commercialization of inverted PSCs. Herein, a facile passivation approach using an alcohol‐soluble small molecule as passivation material is proposed. 2‐Mercaptoimidazole acts as a bridge to cross‐link the perovskite layer and hole transport layer, which reduces interfacial recombination and accelerates carrier transport from perovskite to PEDOT:PSS. As a result, champion devices with a power conversion efficiency of 20.68% and hysteresis free are obtained.