The role of zinc precursor concentration in modulating the structural, optical, and electrical properties of sol-gel derived CZTS thin films

Abstract

This study reports on CZTS thin films fabricated by sol–gel spin coating using zinc acetate dihydrate, copper acetate dihydrate, tin chloride, and thiourea dissolved in methanol with monoethylamine as a stabilizer. The films were annealed rapidly at 540 °C by using an RTP furnace. Results show the significant influence of zinc concentration on films’ properties with band gap evolution between 1.46 and 1.7 eV, along with high absorption coefficients exceeding 10⁴ cm⁻¹ in the visible range. Structurally, the films evolved from poorly crystalline at low Zn content to well- crystallized, (112)-oriented kesterite near stoichiometry. However, excessive Zn caused slight degradation in crystallinity, likely from defect formation or ZnS phase segregation, consistent with SEM observations. Electrical measurements revealed resistivity values of 13–2.6×10² kΩ/□ and carrier concentrations of 10¹⁷–10²⁰ cm⁻³. These findings signify the critical role of Zn in tuning the structural, optical, and electrical characteristics of CZTS films, advancing their optimization for photovoltaic applications