Promoting Charge‐Carriers Dynamics by Relaxed Lattice Strain in A‐site‐Doped Halide Perovskite for Photocatalytic H 2 Evolution

Because of the unique and superior optoelectronic properties, metal halide perovskites (MHPs) have attracted great interest in photocatalysis. Element doping strategy is adopted to modify perovskite materials to improve their photocatalytic performance. However, the contribution of bare doping‐site onto photocatalytic efficiency, and the correlation between doping locations and activity have not yet to be demonstrated. The unique properties of non‐active alkali metals promoted us to systematically explore the potential of A‐site‐doped MHPs for photocatalysis. Herein, we dope potassium (K + ) into CsPbBr 3 via an anti‐solvent precipitation method and first reveal that the occupied locations of K + in CsPbBr 3 is lattice incorporation rather than surface segregation, which would change from A‐site substitution to interstitial site in lattice with the increase of K + concentrations. Taking hydrogen (H 2 ) evolution as a model reaction, photocatalytic activity of CsPbBr 3 after K + doping could be significantly improved ~11‐fold with A‐site substitution, which is superior to that of interstitial site doping. Moreover, other alkali metals including lithium (Li), sodium (Na), and rubidium (Rb) doping give the same results. The structure of photocatalysts during reaction confirmed the contribution of A‐site doping onto enhanced photocatalytic activity. Mechanistic insights show it is a result of the relaxed lattice strain induced promoted charge‐carriers dynamics and upward shifting of band after K + A‐site doping.