Ultraviolet–Visible-Near-Infrared\nBroadband\nPhotodetector Enabled by Cs<sub>2</sub>AgBiBr<sub>6</sub>: Sn/Conjugated\nPolymer Heterojunction

Broadband photodetectors covering ultraviolet (UV) to\nnear-infrared\n(NIR) wavelengths play an essential role in communications, imaging,\nand biosensing. Developing a single photodetector with a broadband\noptical response operating at room temperature can significantly reduce\nthe complexity and cost of receiver systems for multispectral applications.\nIn this work, utilizing the porous structure characteristics of Cs<sub>2</sub>AgBiBr<sub>6</sub>:Sn thin films, a self-powered detector\nwith broad spectral response (UV–vis-NIR) was achieved by constructing\nan effective Cs<sub>2</sub>AgBiBr<sub>6</sub>:Sn/PDPP3T heterojunction.\nThis photodetector possesses a broad response spectrum from 350 to\n950 nm with an average detection rate exceeding 10<sup>11</sup> Jones\nand maintains excellent photoelectric performance over two months.\nSn<sup>2+</sup> doping effectively reduces the bandgap of Cs<sub>2</sub>AgBiBr<sub>6</sub>, enhancing its near-infrared absorption and optimizing\nenergy level alignment with conjugated polymer (diketopyrrolopyrrole-terthiophene,\nPDPP3T). More importantly, the porous structure derived from Sn doping\nsignificantly improves carrier extraction and transport under a near-infrared\nlight response at the heterojunction interface. Utilizing its broad\nspectral response characteristics in the UV–vis-NIR range,\na novel information transfer and encryption system employing full\noptical modulation has been realized within a single perovskite photodetector.\nThis work provides a new approach to fabricating lead-free double\nperovskite broadband photodetectors with potential applications in\nphotonic devices.