Enhancing the Ferroelectricity of <scp> MAPbI ₃ </scp> via Hydroxyl Groups to Boost Photocatalytic Performance

Introducing ferroelectric spontaneous polarization (Ps) electric field to suppress the recombination of photogenerated carriers is crucial for enhancing catalytic activities. Herein, we report a strategy to effectively facilitate the ferroelectricity and charge carrier behavior by compositing MAPbI 3 with hydroxyl‐containing (EOA) 2 PbBr 4 . Density functional theory calculations reveal that the hydroxyl groups will alter the orientation of polar MA + ions, leading to a more uniform alignment with the polarization direction in MAPbI 3 . The ferroelectric‐related piezoelectric constant and spontaneous electric potential demonstrate significant improvements, reaching 43.81 pm V −1 and −876.2 mV, respectively, as measured by piezoresponse force microscopy and kelvin probe force microscope. Furthermore, the increase in the intensity of the steady‐state surface photovoltage (SPV) signal and the slow attenuation of the transient SPV signal in (EOA) 2 PbBr 4 /MAPbI 3 indicate an enhanced Ps electric field, enabling desirable spatial separation of photogenerated carriers. Moreover, photocatalytic CO 2 reduction shows that the CO production rate of the (EOA) 2 PbBr 4 /MAPbI 3 reached 90.37 μmol g −1 , representing a 2.5‐fold increase compared to MAPbI 3 . Overall, this work presents a novel approach to designing high‐performance halide perovskite photocatalytic materials by manipulating ferroelectricity effects through functional groups.