Efficient and Moisture-Stable Inverted Perovskite Solar Cells via n-Type Small-Molecule-Assisted Surface Treatment

Defect states at the surface and grain boundaries of perovskite films have been known to be major determinants impairing the optoelectrical properties of perovskite films and the stability of perovskite solar cells (PeSCs). Herein, an n-type conjugated small-molecule additive based on fused-unit dithienothiophen[3,2-b]-pyrrolobenzothiadiazole-core (JY16) is developed for efficient and stable PeSCs, where JY16 possesses the same backbone as the widely used Y6 but with long-linear n-hexadecyl side chains rather than branched side chains. Upon introducing JY16 into the perovskite films, the electron-donating functional groups of JY16 passivate defect states in perovskite films and increase the grain size of perovskite films through Lewis acid-base interactions. Compared to Y6, JY16 exhibits superior charge mobility owing to its molecular packing ability and prevents decomposition of perovskite films under moisture conditions owing to their hydrophobic characteristics, improving the charge extraction ability and moisture stability of PeSCs. Consequently, the PeSC with JY16 shows a high power conversion efficiency of 21.35%, which is higher than those of the PeSC with Y6 (20.12%) and without any additive (18.12%), and outstanding moisture stability under 25% relative humidity, without encapsulation. The proposed organic semiconducting additive will prove to be crucial for achieving highly efficient and moisture stable PeSCs.