Unveiling the impact of vacuum annealing levels on physical properties of ZnTe thin films for solar cell applications

Abstract

The high performance CdTe solar cells suffer from the back contact problem where the ZnTe is found as one of the suitable back contact materials. The present work reports the influence of vacuum annealing on the physical properties of ZnTe films deposited employing the e-beam evaporation technique. The pristine films are subjected to vacuum annealing at 200 °C for 1 h, corresponding to different vacuum levels viz. 10 × 10 −3 mbar, 5 × 10 −3 mbar, and 1 × 10 −3 mbar. The pristine and vacuum annealed ZnTe films have preferred (200) and (111) reflections of the cubic phase. The direct optical energy band gap of ZnTe films is achieved in the range of 2.58–2.76 eV. All the films are found ohmic in nature and the AFM images of vacuum annealed ZnTe films showed hill-like topographies where surface roughness is altered with vacuum level. Thus, the properties of ZnTe films have been considerably influenced by post-annealing treatment at different vacuum levels. • Impact of vacuum annealing levels on physical properties of ZnTe films is reported. • Pristine and vacuum annealed films crystallized along (200) and (111) preferred peaks, respectively. • Optical energy band gap of ZnTe films is found in 2.58–2.76 eV range. • AFM images of vacuum annealed ZnTe films showed hill-like topographies. • Findings demonstrated that vacuum annealing levels modify the properties of films.