Temperature-dependent properties of Cu-doped ZnTe thin films deposited on ultra-thin glass substrates via RF magnetron sputtering

This study investigates the viability of Cu-doped ZnTe as a potential back surface field (BSF) layer on flexible CdTe thin-film solar cells, examining its structural, morphological, optical, and electrical properties. ZnTe, 5%, and 8% Cu-doped ZnTe were deposited on ultra-thin glass (UTG) substrates using the radio frequency (RF) magnetron sputtering approach at varying substrate temperatures from room temperature to 300 °C. The finding reveals that the surface morphology significantly changes as the substrate temperature increases. Besides, incorporating Cu into ZnTe resulted in a denser and rougher surface, likely due to material densification and accelerated grain growth at higher temperatures. X-ray diffraction (XRD) analysis indicated that the crystallite size of the ZnTe and Cu-doped ZnTe increased with higher temperatures. Optical spectroscopy results demonstrated an increase in the optical band gap of ZnTe with increasing substrate temperature, while Cu-doping introduced a significant variability in the bandgap, particularly at different doping levels. In terms of electrical properties, ZnTe thin films exhibited carrier concentrations around 10 14 cm −3 . Conversely, the introduction of 5% and 8% Cu into ZnTe increased carrier concentrations, ranging from 10 17 to 10 20 cm −3 , respectively, depending on substrate temperature and the amount of Cu concentration. Introducing Cu in the ZnTe structure may modify the characteristics of ZnTe thin films, potentially influencing its suitability as a BSF layer in CdTe solar cells by affecting its structural, optical, and electrical properties. • Adding 5% and 8% Cu to ZnTe enhanced carrier concentrations and conductivity. • Higher substrate temperatures during deposition led to larger crystallite sizes. • Band gap of ZnTe increased from 2.11 eV to 2.18 eV with higher temperatures. • XRD analysis showed improved crystallinity in ZnTe films with Cu at 300 °C. • Cu incorporation in ZnTe resulted in a denser and rougher morphology.