Flexible Broadband Photodetector Based on AgI/Fe-Doped PbS Type-II Heterojunction

Flexible photodetectors are increasingly important for emerging wearable and portable electronic systems, where mechanical adaptability and low-weight substrates are essential. Motivated by this need, the present work explores a paper-based AgI/Fe-doped PbS heterostructure photodetector fabricated using a simple successive ionic layer adsorption and reaction (SILAR) technique, demonstrating broadband UV–Vis–NIR sensitivity, reliable photoswitching behavior, and strong mechanical stability under repeated bending. This work presents a distinct AgI/Fe-doped PbS heterostructure photodetector fabricated on a cellulose paper substrate through a simple and inexpensive SILAR technique. XRD results confirm a higher crystalline nature and the coexistence of AgI and Fe-doped PbS phases, while SEM studies reveal a distinctly nanostructured surface morphology. Energy dispersive spectrometry (EDS) is performed to confirm the elemental quantification, especially to obtain the doping profile. UV–Vis absorption studies display wide spectral coverage, with bandgap values of 2.8 eV for AgI and 1.26 eV for Fe-doped PbS, ensuring strong photodetection capability across multiple wavelength regions. The detector exhibits rapid switching characteristics, with response/recovery times of 1.60 s/3.12 s (for UV), 2.98 s/2.13 s (for visible), and 1.37 s/1.64 s (for NIR), which are notably higher than those of other flexible photodetectors. It further achieves improved detectivity values of 13.20 × 108 Jones (for UV-395 nm), 55.87 × 108 Jones (for visible-550 nm), and 18.70 × 108 Jones (for NIR-780 nm), along with stable responsivities of 0.15 mA/W (for UV), 0.66 mA/W (for visible), and 0.21 mA/W (for NIR). The incorporation of AgI and Fe-doped PbS improves charge separation and carrier transport, enabling effective broadband UV–Vis–NIR sensing. In comparison to previous studies, this device provides an uncommon blend of room-temperature fabrication, high flexibility, and detailed multiwavelength performance analysis, establishing it as a practical and sustainable photodetector platform. Moreover, the device maintains a stable performance after 1200 mechanical bending cycles, highlighting its robustness for flexible and wearable electronics. With its broadband response, fast photoswitching, and structural durability, the AgI/Fe-doped PbS heterojunction photodetector presents strong potential for diverse optoelectronic applications.