Two‐Dimensional Hydrazopyridinium Lead Iodide Perovskite Photodetectors With Broadband Sensitivity and Photoconductive Gain

Broadband photodetectors with enhanced ultraviolet sensitivity are critical for applications including environmental monitoring and optical communications, yet achieving high performance at low operating voltages remains challenging. Hydrazopyridinium lead iodide (HPDLI), a two‐dimensional Dion–Jacobson (DJ) perovskite synthesized via in situ reduction of 4,4′‐azopyridine, achieves a bandgap of 2.13 eV, among the lowest reported for n = 1 lead halide systems, through an orthorhombic crystal structure with nearly linear Pb─I─Pb bonding (179.46°). This geometry maximizes metal‐halide orbital overlap, extending the broadband response toward the visible, with wavelength‐dependent absorption coefficients giving stronger sensitivity at shorter (deep‐UV) wavelengths. Lateral photodetectors exhibit 6 A/W responsivity, 1.01 × 10 12 Jones shot‐noise‐limited detectivity, and 2900% external quantum efficiency at 254 nm under a low 0.2 V bias. High‐gain response is consistent with trap‐mediated photoconductive mechanisms and a proposed type‐II band alignment, where hydrazopyridinium cations may extend carrier lifetimes. Millisecond rise/fall times (40/70 ms), preliminary stability screening (2000‐s cyclic and continuous‐illumination protocols, a 48 h/80% RH switching‐shape comparison), and retention of characteristic PXRD peak positions after 5 months of ambient storage support crystal engineering as a route to energy‐efficient UV‐to‐visible photodetection, though longer, quantitative operational testing remains necessary.