The synthesis of metal halide perovskite/perovskitoid (MHP) photocatalysts with well-defined morphologies and facet-specific redox activity is technically challenging. Herein, using surfactants to control the arrangement of 0D facet-shared [Bi2I9]3– dioctahedra building blocks, we successfully fabricated ordered perovskite Cs3Bi2I9 hexagonal prisms (CBI-HPs). Using Co2+ oxidation and Pt4+ reduction as redox probes, photoexcited holes were shown to spatially migrate to the edge (100) facets while photoexcited electrons migrated to the (006) basal facets, respectively. Density functional theory revealed that the built-in potential of the facet junction between (100) and (006) facets was ∼130 meV. Because of the well-separated redox facets, the photocatalytic hydrogen evolution rate of ordered CBI-HPs via hydroiodic acid splitting reached 1504.5 μmol/h/g, which is 22.1 times that of a disordered CBI photocatalyst. This work guides the rational design of high-performance MHP photocatalysts for solar energy conversion and other applications.

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Slow charge kinetics and unfavorable CO2 adsorption/activation strongly inhibit CO2 photoreduction. In this study, a strain‐engineered Cs3Bi2Br9/hierarchically porous BiVO4 (s‐CBB/HP‐BVO) heterojunction with improved charge separation and tailored CO2 adsorption/activation capability is developed. Density functional theory calculations suggest that the presence of tensile strain in Cs3Bi2Br9 can significantly downshift the p‐band center of the active Bi atoms, which enhances the adsorption/activation of inert CO2. Meanwhile, in situ irradiation X‐ray photoelectron spectroscopy and electron spin resonance confirm that efficient charge transfer occurs in s‐CBB/HP‐BVO following an S‐scheme with built‐in electric field acceleration. Therefore, the well‐designed s‐CBB/HP‐BVO heterojunction exhibits a boosted photocatalytic activity, with a total electron consumption rate of 70.63 µmol g−1 h−1, and 79.66% selectivity of CO production. Additionally, in situ diffuse reflectance infrared Fourier transform spectroscopy reveals that CO2 photoreduction undergoes a formaldehyde‐mediated reaction process. This work provides insight into strain engineering to improve the photocatalytic performance of halide perovskite.

The performance of the blue perovskite light-emitting diodes (PeLEDs) is limited by the low photoluminescence quantum yields (PLQYs) and the unstable emission centers. In this work, we incorporate sodium bromide and acesulfame potassium into a quasi-2D perovskite to control the dimension distribution and promote the PLQYs. Benefiting from the efficient energy cascade channel and passivation, the sky-blue PeLED has an external quantum efficiency of 9.7% and no shift of the electroluminescence center under operation voltages from 4 to 8 V. Moreover, the half lifetime of the devices reaches 325 s, 3.3 times that of control devices without additives. This work provides new insights into enhancing the performance of blue PeLEDs.