Optimization of Thermal Budgets for Zn‐Doped PbS Flexible Coatings via Chemical Spray Pyrolysis

This study systematically investigates the impact of depositional thermal budgets on the structural, optical, and electrical properties of zinc‐doped lead sulfide (Zn‐doped PbS) thin coatings (300 nm) synthesized over flexible polyimide substrates via cost‐effective chemical spray pyrolysis. The films were fabricated under substrate temperatures regulated at 300, 325, and 350 °C. X‐ray diffraction confirmed a pure cubic rock‐salt phase. Elevating the thermal budget to 350 °C systematically decreased the full width at half maximum of the dominant (200) peak from 0.2558° to 0.1279°, enhancing crystalline ordering and promoting crystallite size growth from 33.79 to 64.25 nm due to improved adatom mobility. Scanning electron microscopy (SEM) evaluations revealed a profound transition from dense, fine nanostructured grains to a highly continuous and fully coalesced crystalline matrix with increasing thermal budget. Photoluminescence spectroscopy revealed symmetric emission profiles, yielding a wide optical bandgap of 4.13 eV at 325 °C driven by quantum confinement, Zn‐alloying, and Burstein–Moss effects. Hall effect measurements indicated a persistent p‐type conduction. Increasing the temperature minimized electrical resistivity from 1540 to 910 Ω m while inflating the carrier concentration from 45  × 10 ¹² to 112 × 10 ¹²  cm ⁻³ via grain‐boundary passivation. These results demonstrate an effective nonvacuum strategy to tailor chalcogenide coatings for flexible optoelectronics.