Synergistic Bimolecular Passivation Stabilizing Surface States for High Performance HTL‐Free Inverted Perovskite Solar Cells

ABSTRACT The inevitable photothermal‐induced desorption of functional molecules at the perovskite film surface would resurge the passivated surface defect states and cause severe recombination, thereby affecting both photovoltaic performance and stability of perovskite solar cells (PSCs). Here, we report a synergistic bimolecular passivation (SBP) strategy by employing 2‐methylpropanimidamide hydrochloride (MPACl) to fix phenethylammonium (PEA + ) ligands extensively used at the perovskite film surface, achieving a stable and well passivated surface. As revealed, SBP strategy significantly inhibited the interface nonradiative recombination and enhanced the carrier transport, along with optimizing the interfacial energy level alignment. As a result, for the promising hole‐transport layer (HTL)‐free PSCs, the target device achieved a remarkable PCE of 26.51% (certified at 26.03%) with a V OC of 1.204 V, corresponding to a mere 356 mV deficit for 1.56 eV perovskites. This further boosts the record efficiency of HTL‐free PSCs. Meanwhile, the encapsulated device can retain over 95% of their original PCE after 1300 h of light soaking. Our work addressed successfully the above thorny issue and provides an effective way to realize both high efficiency and stability PSCs.