The development of green, sustainable, and economical chemical processes represents a cornerstone challenge within chemistry today. Semiconductor heterogeneous photocatalysis is currently utilized within a wide variety of societally impactful processes, spanning reactions such as hydrogen production and CO2 conversion, to the organic transformation of raw materials for value-added chemicals. Metal halide perovskites (MHPs) have recently emerged as a new promising class of cheap and easy to make photocatalytic semiconductors, though their unstable ionically bound crystal structure has thus far restricted widespread application. In this Review, we examine the issues hampering MHP-based photocatalysis and highlight the general approaches being taken to achieve promising and stable photocatalytic reaction environments. Specifically, we outline the adoption of (1) halogen acid solutions (i.e., HX; X = I or Br) for hydrogen evolution reactions, (2) relatively low-polarity solvents for CO2 photoreduction and organic transformations, and (3) the encapsulation of perovskites for CO2 reduction and water splitting. Further, we detail the measures being taken to arrive at intrinsically stable photocatalytic materials, removing the need for atypical environments. With each technology offering unique sets of benefits and challenges, we conclude by outlining potentially promising opportunities and directions for metal halide perovskite-based photocatalysis research moving forward.

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.

Metal halide perovskites with direct band gap and strong light absorption are promising materials for harvesting solar energy; however, their relatively narrow band gap limits their redox ability when used as a photocatalyst. Adding a second semiconductor component with the appropriate band structure offsets can generate a Z-scheme photocatalytic system, taking full advantage of the perovskite’s intrinsic properties. In this work, we develop a direct Z-scheme photocatalyst based on formamidinium lead bromide and bismuth tungstate (FAPbBr3/Bi2WO6) with strong redox ability for artificial solar-to-chemical energy conversion. With desirable band offsets and strong joint redox potential, the dual photocatalyst is shown to form a semicoherent heterointerface. Ultrafast transient infrared absorption studies employing selective excitation reveal synergetic photocarrier dynamics and demonstrate Z-scheme charge transfer mechanisms. Under simulated solar irradiation, a large driving force photoredox reaction (∼2.57 eV) of CO2 reduction coupled with benzyl alcohol oxidation to benzaldehyde is achieved on the Z-scheme FAPbBr3/Bi2WO6 photocatalyst, harnessing the full synergetic potential of the combined system.

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.

Defect engineering in photocatalysts represents a fundamental method toward tailoring their solar-to-chemical energy conversion performance, although determining the nature and impact of subsurface defects remains challenging. Single-unit-cell Bi2WO6 monolayers, forming a sandwich-like structure, [BiO]+–[WO4]2––[BiO]+, exhibit promising photocatalytic performance and are an ideal system for isolating subsurface defects. We report the single-step synthesis of Bi2WO6 monolayers rich in stable interior W vacancies and characterize their influence on the physical properties necessary for effective photocatalytic surface reactions. Defect-rich monolayers benefit from enhanced visible-light absorption and photocarrier transport, boosting the solar photocatalytic oxidation of benzylic alcohols by 140% at no cost to selectivity or stability. This work highlights the importance of subsurface defects within surface-driven photocatalytic applications and prescribes a general strategy for their isolated study via 2D compounds exhibiting symmetric surface termination.