Exploring the impact of lithium doping on the optoelectrical, optical, and electrical properties of spray-deposited ZnS thin films

In this study, ZnS and lithium-doped zinc sulfide (Li: ZnS) films were synthesized using a cost-effective spray pyrolysis technique, with lithium doping concentrations of 3, 6, and 9 wt%. X-ray diffraction (XRD) analysis confirmed that both undoped and Li-doped ZnS films exhibit a polycrystalline cubic structure. Structural characterization revealed that the crystallite size initially increased and then decreased as the Li content was raised from 3 to 9 wt%, while the strain and dislocation density followed a similar trend, first decreasing and then increasing with higher Li concentrations. Optical property analysis demonstrated that key parameters, including the refractive index, reflectance, Urbach energy, and absorption coefficient, improved significantly with increasing Li doping. Additionally, optoelectrical properties like optical conductivity, plasma frequency, and optical carrier concentration were enhanced as the Li content increased. Nonlinear optical properties also showed improvement with higher Li doping levels. Electrical measurements indicated that both electrical mobility and carrier concentration increased with Li content, whereas electrical resistivity exhibited an inverse relationship. The study highlights the potential of Li-doped ZnS films as efficient window layers for thin-film solar cells. DC conductivity analysis revealed a reduction in activation energy with increasing Li content. Furthermore, an ITO/Li:ZnS/Sb₂S₃/Au heterojunction was fabricated, and photovoltaic performance evaluation showed a notable enhancement in power conversion efficiency, increasing from 3.59% to 7.98% as the Li doping ratio was raised. These findings highlight the promising optoelectronic and photovoltaic applications of Li-doped ZnS films.