The Eu 2+ /Eu 3+ Redox Sites Stabilize the CsPbBr 3 Perovskite Lattice and Modulate Electron–Phonon Dynamics for Enhanced CO 2 Photoreduction

CsPbBr 3 perovskite nanocrystals have been investigated as photocatalysts for CO 2 reduction owing to their excellent light-harvesting and multi-exciton generation. However, under strong illumination, Pb 2+ migration and reduction to metallic Pb 0 cause lattice collapse and accelerated carrier recombination, severely limiting their stability and photocatalytic performance. Here, we developed a dynamic valence regulation approach using Eu 2+ /Eu 3+ redox couple to enhance lattice stability and improve photocatalytic performance by suppressing Pb 2+ migration and Pb 0 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 CsPbBr 3 exhibits a 6-fold enhancement in CO 2 -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.