The Eu2+/Eu3+ Redox Sites Stabilize the CsPbBr3 Perovskite Lattice and Modulate Electron–Phonon Dynamics for Enhanced CO2 Photoreduction

CsPbBr3 perovskite nanocrystals have been investigated as photocatalysts for CO2 reduction owing to their excellent light-harvesting and multi-exciton generation. However, under strong illumination, Pb2+ migration and reduction to metallic Pb0 cause lattice collapse and accelerated carrier recombination, severely limiting their stability and photocatalytic performance. Here, we developed a dynamic valence regulation approach using Eu2+/Eu3+ redox couple to enhance lattice stability and improve photocatalytic performance by suppressing Pb2+ migration and Pb0 exsolution, modulating phonon coupling, and prolonging hot-carrier lifetimes. Experimental analyses suggest that Eu incorporation, together with mixed Eu valence states, is associated with improved lattice stability and reduced Pb-related destabilization under photocatalytic conditions. Moreover, Eu incorporation strengthens lattice rigidity and reduces electron–phonon coupling, which collectively slows down the thermalization of hot carriers. Transient absorption spectroscopy indicates a nearly 4-fold extension in hot-carrier lifetime compared to the pristine counterpart. As a result, the Eu-modified CsPbBr3 exhibits a 6-fold enhancement in CO2-to-CO conversion activity (300 ± 5 mmol·m−2) and maintains over 80% of its activity after continuous operation for 60 h. This work proposes a synergistic redox-lattice-carrier regulation mechanism, providing insights into the rational design of metal halide perovskite photocatalysts.