Enhancing Weak Light Detection in Single-Crystalline MAPbI₃ Nanowires via Cooling

Photodetectors (PDs) capable of detecting weak light are critical for applications like astronomical observation, quantum computing, cryogenic biomedical imaging, material analysis and precision measurements. Perovskite materials, due to their high carrier mobility, long diffusion lengths, and solution processability, offer substantial advantages in PD performance. In this study, we fabricated high-quality single-crystalline nanowires (NWs) of methylammonium lead iodide (MAPbI 3 ) and developed a high-performance metal–semiconductor-metal PD operating at 85 K. The device demonstrated an extremely low dark current of 3.7 × 10 –13 A (1 V) at 85 K, 4 orders of magnitude lower than at room temperature (RT). Its detectivity exceeded RT performance by a factor of 706, reaching 7.7 × 10 13 Jones, and achieved a phototo-dark current ratio exceeding 10 8 under 532 nm light illumination at 204 mW/cm 2 . As the optical power density decreased to 12 nW/cm 2, detectivity further increased to 2.7 × 10 15 Jones. These improvements are linked to the phase transition from tetragonal to orthorhombic crystal structure, which results in a widened bandgap. At 85 K, thermally excited carriers and ion migration are significantly suppressed, and defect self-annihilation is promoted, leading to a much-reduced dark current. Additionally, the reduced defects lower nonradiative recombination and the ordered molecular arrangement could enhance the generation and transport of photogenerated charge carriers under illumination with a power density above 40 μW/cm 2 (532 nm) at 85 K. This work sets a benchmark for MAPbI 3 PD performance, demonstrating the potential of perovskite-based devices for weak light detection.