Exploiting Bulk Photovoltaic Effect in a Polar Hybrid Perovskite Towards Self‐Powered Detection of Weak Ultraviolet Polarized Light

Weak light detection is essential for achieving high‐performance photodetectors with minimal power consumption; however, it remains challenging due to the high dark current under operating voltage. Herein, a self‐powered photodetector based on a polar perovskite crystal, namely (4‐AMP)PbBr 4 (4‐AMP = 4‐(aminomethyl)‐piperidine), is reported that exhibits exceptional sensitivity to ultraweak ultraviolet (UV) polarized light. (4‐AMP)PbBr 4 crystallizes in a polar space group of P ca2 1 and generates spontaneous polarization that gives rise to a strong bulk photovoltaic effect (BPVE), serving as a driving force for spatial separation/transport of photogenerated carriers. As a result, self‐powered photodetectors using (4‐AMP)PbBr 4 crystals exhibit significantly suppressed current to sub‐pA level in the absence of light, and can be “activated” with ultraweak UV light radiation, showcasing superior photoresponse characteristics. More interestingly, by leveraging its inherent BPVE, the resultant device exhibits intriguing polarization‐sensitive behavior along with a large anisotropic ratio of 8 at 1 µW/cm 2 , among the highest values of the reported polarized light detectors. Even at a polarized light intensity down to 60 nW/cm 2 , the anisotropic ratio can still reach 1.8. Our findings establish a promising platform for energy‐efficient, light‐driven devices with potential applications in self‐powered polarized light detection.