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

Abstract

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 10¹⁴ cm⁻³. Conversely, the introduction of 5% and 8% Cu into ZnTe increased carrier concentrations, ranging from 10¹⁷ to 10²⁰ 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.