Synergistic Passivation and Crystallization Control via a Bifunctional Ionic Liquid for Minimizing Voltage Loss in...

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 Pb²⁺ 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.