Promoting Charge‐Carriers Dynamics by Relaxed Lattice Strain in A‐site‐doped Halide Perovskite for Photocatalytic H2 Evolution

Because of the unique and superior optoelectronic properties, metal halide perovskites (MHPs) have attracted great interests 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. This promoted us to explore the potential of A‐site‐doped MHPs for photocatalysis. Herein, we dope potassium (K+) into CsPbBr3 and first reveal that the occupied locations of K+ in CsPbBr3 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 H2 evolution as a model reaction, photocatalytic activity of CsPbBr3 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 Li, Na, and 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 residual lattice strain induced promoted charge‐carriers dynamics and formed upward shifting of band after K+ A‐site doping.