Optimizing Lead Sulfide Thin Films for Flexible Infrared Photodetectors: Impact of Thickness on Mechanical Durability and Optoelectronic Performance

Lead sulfide (PbS) nanostructures are promising materials for flexible infrared (IR) photodetectors. This study explores the structural, morphological, and optoelectronic characteristics of PbS thin films (100–310 nm) deposited on polyimide substrates to assess performance under mechanical bending. X‐ray diffraction confirms their polycrystalline structure, while energy‐dispersive X‐ray spectroscopy reveals Pb‐deficiency, contributing to acceptor state formation and enhanced photoconduction. The films show excitonic absorption corresponding to the bandgap (1.14 eV) is higher than bulk PbS due to quantum confinement and defects. Ag/PbS‐Poly/Ag devices demonstrate stable IR photoresponse under bending up to 75°, with optimal performance observed in 200 nm films. These exhibit fast photoresponse (3 ms rise, 7 ms decay), high responsivity (2.47 A/W), detectivity (0.75 × 10¹³ Jones), and 66% external quantum efficiency under 1.7 mW cm⁻² illumination. Thicknesses above 200 nm lead to surface cracking and performance loss (>50%) due to strain‐induced degradation. Notably, 200 nm devices maintain stable performance after 500 bending cycles at 60°, confirming their mechanical durability. This work underscores the significance of thickness optimization in flexible IR photodetectors and offers insight into how strain, defects, and charge transport interact in wearable optoelectronics.