The impressive optoelectronic performance and low production cost of metal halide perovskites have inspired applications well beyond efficient solar cells. Herein, we widen the materials engineering options available for the efficient and selective photocatalytic oxidation of benzylic alcohols, an industrially significant reaction, using formamidinium lead bromide (FAPbBr3) and other perovskite-based materials. The best performance was obtained using a FAPbBr3/TiO2 hybrid photocatalyst under simulated solar illumination. Detailed optical studies reveal the synergetic photophysical pathways arising in FAPbBr3/TiO2 composites. An experimentally supported model rationalizing the large conversion enhancement over the pure constituents shows that this strategy offers new prospects for metal halide perovskites in photocatalytic applications.

Inspired by efficient perovskite solar cells, we developed a threecomponent hybrid perovskite-based solar photocatalyst cell, NiO x /FAPbBr 3 /TiO 2 , for C(sp 3 )−H bond activation with high selectivity (∼90%) and high conversion rates (3800 μmol g −1 h −1 ) under ambient conditions. Time-resolved spectroscopy on our photocatalytic cell reveals efficient exciton dissociation and charge separation, where TiO 2 and NiO x serve as the electron-and hole-transporting layers, respectively. The photogenerated charge carriers injected into TiO 2 and NiO x drive the challenging C− H activation reaction via the synergetic effects of their band alignment relative to FAPbBr 3 . The reaction pathway is investigated by controlling the free-radical formation, and we find that C−H activation is mainly triggered by hole oxidation. Besides aromatic alkanes, also the C(sp 3 )−H bond in cycloalkanes can be oxidized selectively. This work demonstrates a generic strategy for engineering highperformance photocatalysts based on the perovskite solar cell concept.

Metal trihalide perovskites are rapidly redefining the landscape of solid-state semiconductors utilized as active medium in photovoltaics and in light generation. Within this materials space, organic-inorganic hybrid formamidinium lead bromide (FAPbBr3) has arisen as a promising candidate for efferent light emitting devices, due to its capacity for sharp and bright green light emissions (530 nm). Herein we have applied a facile single-step ligand-mediated method for phasecontrolled synthesis of FAPbBr3 cube-and rod-shaped nanocrystals (NCs), starting from different ratios of precursor agents. Examining their structural and optoelectronic properties-using a combination of synchrotron X-ray diffraction, X-ray spectroscopy, scanning electron microscopy and steady-state and time-resolved photoluminescence (PL)-we reveal the two NC types to fundamentally differ. While the cube-shaped NCs exhibit properties aligning with that of bulk FAPbBr3, the nanorods exhibit a two-phase microstructure and the coexistence of both a typical cubic perovskite structure alongside the formation of a new low-symmetry monoclinic phase (P2/m). Further, the two-phase nanorods display a bright dual PL emission (peaks centered near 490 nm and 530 nm) and complex luminescence dynamics, properties characteristic of quasi-2D perovskites. The two phase nanorods generation can be assigned to the proton exchange in the presence of excess of FA + during the synthesis.

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