Synergistic Passivation and Crystallization Control via a Bifunctional Ionic Liquid for Minimizing Voltage Loss in Wide‐Bandgap Perovskites

Wide‐bandgap perovskite solar cells (WBG PSCs) are key to high‐efficiency tandem photovoltaics but suffer from severe open‐circuit voltage ( V OC ) loss, primarily due to non‐radiative recombination losses induced by high bromine content. Here, we demonstrate a bifunctional ionic liquid (ILs) additive, 1,3‐di(cyanoethyl)‐imidazolium thiocyanate (ILSCN), engineered to mitigate multiple recombination loss pathways synergistically in wide‐bandgap PSCs. The ILSCN molecule features cooperative cation‐anion functionality: the thiocyanate anions effectively fill halide vacancies while the ‐CN group on functionalized cations coordinate with uncoordinated Pb 2+ sites. This dual‐action not only modulates crystal growth orientation and enhances nucleation density but also suppresses halide migration and non‐radiative recombination. As a result, 1.83‐eV WBG PSCs incorporating ILSCN achieve a significantly improved V OC of 1.35 V and a stabilized power conversion efficiency (PCE) of 18.4%. Especially, the devices retain 84% of their initial efficiency after nearly 500 h of continuous illumination. This work demonstrates a facile synergistic ionic liquid strategy in defect passivation, crystallization control, and overcoming the performance limitations of WBG perovskite photovoltaics.