Intricate Reaction Pathways on CH 3 NH 3 PbI 3 Photocatalysts in Aqueous Solution Unraveled by Single-Particle Spectroscopy.

Organic-inorganic hybrid perovskites such as MAPbI 3 (MA + = CH 3 NH 3 + ) have emerged as promising materials for solar cells and light-emitting devices. Despite their poor stability against moisture, perovskites work as hydrogen-producing photocatalysts or photosensitizers in perovskite-saturated aqueous solutions. However, the fundamental understanding of how chemical species or support materials in the solution affect the dynamics of the photogenerated charges in perovskites is still insufficient. In this study, we investigated the photoluminescence (PL) properties of MAPbI 3 nanoparticles in aqueous media at the single-particle level. A remarkable PL blinking phenomenon, along with significant decreases in the PL intensity and lifetime compared to those in ambient air, suggested temporal fluctuations in the trapping rates of photogenerated holes by chemical species (I - and H 3 PO 2 ) in the solution. Moreover, electron transfer from the excited MAPbI 3 to Pt-modified TiO 2 proceeds in a concerted fashion for photocatalytic hydrogen evolution under the dynamic solid-solution equilibrium condition.