Thermal growth kinetics and comprehensive tuning of structural, optical, and electrical transport properties in flexible PbS thin films on polyimide substrates via spray pyrolysis

This study investigates the thermal growth dynamics and optoelectronic tuning of flexible lead sulfide (PbS) thin films synthesised on polyimide (PI) substrates via chemical spray pyrolysis. An aqueous precursor solution of lead nitrate and thiourea (1:1 molar ratio) was atomised at 5 ml/min onto heated PI substrates. By systematically varying the substrate temperature from 300 to 350 °C, a 330% enhancement in Hall mobility (7.65–32.90 cm²/V·s) and a five-fold increase in carrier concentration (reaching 40.13 × 10¹¹ cm−3) were achieved. Structural analysis confirmed improved crystallinity with crystallite growth from 28.4 to 53.1 nm, reducing dislocation density by ∼70%. Optical investigations revealed a tunable energy bandgap (1.44–1.65 eV). This pronounced blue shift from the bulk value (∼0.41 eV) is rationalised by the synergistic effects of high interfacial tensile strain from the PI substrate and partial oxygen incorporation forming wide-bandgap amorphous phases, rather than macro-scale quantum confinement alone. These results demonstrate that atmospheric spray pyrolysis can yield high-performance transport metrics comparable to vacuum-based techniques, establishing a low-cost performance benchmark for flexible infrared optoelectronic applications.