Interface regulation with D-A-D type small molecule for efficient and durable perovskite solar cells

D-A-D type organic small molecules as interfacial passivation layers enhanced the performance of perovskite solar cells, with particular emphasis on the role of alkyl chain length in modulating interfacial contact. Organic molecule passivation of perovskite surfaces has emerged as a promising strategy for efficient and durable perovskite solar cells (PSCs). While many materials have been reported, the optimization of molecular structure for the best passivation effect remains of significant interest but lacks sufficient study. In this work, we designed and synthesized three novel donor–acceptor-donor (D-A-D) type conjugated organic small molecules with varying alkyl chain lengths to regulate the interface between perovskite and Spiro-OMeTAD. Among them, the OSIT molecule, which features an n-octyl side chain of optimal length, demonstrated a balanced interfacial contact and interaction with the perovskite surface. Beyond the passivation effect of the electron-rich C=O group on undercoordinated Pb 2+ defects, OSIT optimizes energy level alignment and improves charge extraction by acting as an efficient hole transport channel. As a result, PSCs with OSIT interfacial layer achieved an exceptional efficiency of 25.48% and a high open-circuit voltage of 1.18 V. Furthermore, the durability of unencapsulated devices was significantly enhanced under various environmental conditions, maintaining 93.7% of their initial efficiency after 1000 h of maximum power point tracking in a nitrogen atmosphere. This study provides valuable insights into the rational design of D-A-D type materials for effective interface modification in PSCs.