The existence of a defective area composed of nanocrystals and amorphous phases on a perovskite film inevitably causes nonradiative charge recombination and structural degradation in perovskite photovoltaics. In this study, a stoichiometric etching strategy for the top surface of a defective cesium lead halide perovskite is developed by using ionic liquids. The dissolution of the original defective area substantially exposes the underlying perovskite, which is a high‐quality surface with retained stoichiometry and lattice continuity. The ionic liquid molecules are adsorbed on the perovskite surface via Coulombic interactions and passivate the undercoordinated surface lead centers. Such a structural modulation considerably reduces the trap density of the perovskite devices and enables a record power conversion efficiency of 17.51% and an open‐circuit voltage of 1.37 V of the CsPbI2Br cell with a perovskite bandgap of 1.88 eV. This work provides a novel technical route to improve the efficiency and environmental resilience of perovskite‐based optoelectronic devices.

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Inorganic perovskite solar cells have attracted wide attention due to their excellent thermodynamic stability and suitable bandgap as the top absorber materials for tandem solar cells. However, the power conversion efficiencies (PCEs) of the perovskite cells can be considerably limited by the non‐radiative energy loss caused by grain boundaries and surfaces. Here, the synergistic functionalization of CsPbI2Br perovskites was demonstrated by using a metal‐organic complex. Experimental and theoretical studies revealed that the adsorption energy of the passivator could be a good descriptor to evaluate the surface passivation effect. The cooperative adsorption could eliminate the unsaturated surface sites, reduce the surface energy, and thus benefit device performance. The CsPbI2Br solar cells passivated by zinc diethyldithiocarbamate showed a champion power conversion efficiency of 17.15 % and retained 94 % of their initial efficiency after working under 1 sun illumination for 720 h in N2 atmosphere.

The Cover Feature shows a diethyldithiocarbamate molecule cooperating with a Zn cation to passivate the surface of a perovskite film. This strategy optimized the surface and realized power conversion efficiencies (PCEs) over 17 %. More information can be found in the Research Article by Y. Shi, J. He, H. Lian, et al.