Ionic liquid tailoring defect/interface-induced recombination loss toward efficient Dion-Jacobson quasi-2D perovskite solar cells

Dion-Jacobson (DJ) quasi-two-dimensional (quasi-2D) perovskites have emerged as a potential photovoltaic material due to their versatile n-layer variation and superior stable structure. However, compared to their three-dimensional counterparts, the power conversion efficiency (PCE) of quasi-2D perovskite solar cells (PSCs) reported to date still lags behind the detailed balance (DB) limit for single-junction PSCs, which derives from the presence of non-radiative recombination loss. Herein, we demonstrated that the defect/interface-induced recombination loss in DJ quasi-2D PSCs could be significantly suppressed by introducing a green ionic liquid methylammonium acetate (MAAc) into (BDA)(MA)4Pb5I16 (n = 5) (BDA, 1,4-butanediamine) perovskite precursor. Both the film quality of 2D perovskites and the interfacial property of perovskite/charge transporting layer (CTL) were improved after introducing MAAc in precursor solution. Correspondingly, a champion PCE of 18.76 % with a remarkable open-circuit voltage (Voc) of 1.24 V was achieved. Through the quantitative loss analysis, which involved the calculation of photovoltaic parameters relative to DB limit and quasi-Fermi level splitting values, the improvement of PCE and Voc by introducing MAAc was mainly attributed to the reduction of defects in perovskite films and at perovskite/CTL interfaces, and the optimization of interfacial energy-level alignment. The present work provides a green solvent strategy for improving the performance of quasi-2D PSCs, and offers an insight into the fundamental physics of non-radiative recombination loss tailored by ionic liquid.