The Role of Ending Groups in Nonfullerene Acceptors for Interfacial Modification in Perovskite Solar Cells

The defects in organic–inorganic halide perovskite films are detrimental to device efficiency and the stability of perovskite solar cells (PSCs). Interfacial modification is a universal way to passivate defects and improve device performance. However, the effect of terminal groups in non‐fullerene acceptors (NFAs) on interfacial passivation in PSCs is still under investigation. Here, we demonstrate that ending groups of NFAs play an important role in interfacial modification. By comparing four different non‐fullerene molecules with different ending groups (ITCC, ITIC, IT‐M, IT‐4F) applied as passivation layer, we found that devices with ITCC showed better performance, which was attributed to the assistance of the S atom in the ending group of ITCC enhancing adsorption to the perovskite surface compared to the ITIC case, leading to a tighter contact with the perovskite layer and better charge transfer. As a result, in FA 0.85 MA 0.15 Pb(I 0.85 Br 0.15 ) 3 based PSCs, we achieved a power conversion efficiency of 21.21% and an open‐circuit voltage of 1.15 V. Meanwhile, the device with ITCC showed extraordinary stability, maintaining more than 90% initial efficiency after 2000 h. The findings of this work could provide deeper insights into designing novel passivation materials at molecular scale for high efficiency and stable PSCs.