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We report the in operando visualization of the photocatalytic turnovers on single eosin Y (EY) through a redox-induced photoblinking phenomenon. The photocatalytic cyclization of thiobenzamide (TB) catalyzed by EY was investigated. The analysis of the intensity-versus-time trajectories of single EYs revealed the kinetics and dynamics of the elementary photocatalytic turnovers and the heterogeneity of the activity of individual EYs. The quenching turnover time showed a fast population and a slow population, which could be attributed to the singlet and triplet states of photoexcited EY. The slow quenching turnovers were more dominant at higher TB concentrations. The activity heterogeneity of EYs was studied over a series of reactant concentrations. Excess quenching reagent was found to decrease the percentage of active EYs. The method can be broadly applied to studying the elementary processes of photocatalytic organic reactions in operando. 

2D perovskites are relatively stable but possess poor charge transport compared to 3D perovskites. To boost charge transport, novel 2D perovskites mixed with 3D perovskites are developed, where Pb²⁺are partially substituted by the heterovalent neodymium cations (Nd³⁺) within both 2D and 3D perovskites (termed Nd³⁺‐substituted 2D:3D mixed perovskites. Systematical studies reveal that the Nd³⁺‐substituted 2D:3D mixed perovskites possess larger crystals, superior crystallinity, suppressed non‐radiative charge recombination, and enhanced and balanced charge transport compared to the 2D:3D mixed perovskites. As a result, perovskite photovoltaics based on the Nd³⁺‐substituted 2D:3D mixed perovskites exhibit a power conversion efficiency of 22.11%, a photoresponsibility of over 700 mA W⁻¹, a photodetectivity of 4.29 × 10¹⁴ cm Hz^1/2 W⁻¹, a linear dynamic range of 165 dB at room temperature, and dramatically boosted stability. These results demonstrate that, a facile way is developed to realize high‐performance perovskite photovoltaics through partially heterovalent substituted Pb²⁺by Nd³⁺within 2D:3D mixed perovskites.