Copper (II) Chloride Mediated Interfacial Permeation for High-Efficient and Stable Wide-Bandgap Perovskite Solar...

Wide-bandgap (WBG) perovskite solar cells (PSCs) are crucial for high-efficiency tandem photovoltaics. However, their performance is severely limited by lattice disorder at the buried interface, which leads to the accumulation of deep-level defects and interfacial morphological inhomogeneities, thereby inducing pronounced non-radiative recombination and halide segregation. Here, we report a copper (II) chloride (CuCl₂) mediated interfacial permeation strategy that achieves the redox mediation and halide coordination, thereby stabilizing the interfacial chemical state, suppressing the formation of deep-level defects. The strategy effectively suppresses lattice disorder at the buried interface, while simultaneously constructing an efficient hole-transfer structure, thus enhancing interfacial phase stability and charge-transport properties. Consequently, our modified 1.79 eV WBG PSCs exhibit minimized non-radiative recombination losses and superior charge transport, achieving state-of-the-art performance with an open circuit voltage (V_OC) of 1.35 V, a fill factor of 84.29%, and power conversion efficiency (PCE) of 21.24%, one of the highest reported so far. The device can maintain 91% of its original efficiency after 1400 h of maximum power point tracking.