Effect of thermal annealing on physical properties of Cu-doped ZnTe thin films: Functionality as interface layer

Abstract

Achieving a high quality interface is of great importance in CdTe based solar cells, as it appreciably inhibits interfacial recombination and consequently improves the photovoltaic performance. The low carrier density of CdTe absorber contributes to formation of back contact Schottky barrier which acts as diode setup in opposition to the CdS/CdTe junction. To overcome this problem, the Copper doped Zinc Telluride (ZnTe:Cu) material is estimated to be a good nominee for such interface layer due to its high chemical immovability and appropriate band gap alignment with CdTe absorber. Hence, the present work demonstrates thermal annealing evolution to 200 nm thin resistive heating grown ZnTe:Cu 1 % films to find their feasibility as back/rear contact material in the CdTe based superstrate solar cell devices. The structural analysis revealed that as deposited and annealed ZnTe:Cu 1 % films have (103) preferred reflection with cubic phase and crystallite size is enhanced from 22 nm to 42 nm with annealing. The optical transmittance is varied with annealing and the direct optical energy band gap is found within the range of 2.10–2.74 eV. The pristine and annealed films showed ohmic behavior and the AFM images displayed hill like topographies. Smaller to larger size spherical shaped grains and non-uniform cylindrical shaped grains morphology is obtained in FESEM images whereas the EDS patterns confirmed successful deposition of ZnTe:Cu 1 % thin films. The obtained results signify that the 300 °C annealed ZnTe:Cu 1 % films might be considered as interface layer material for the fabrication of CdTe based solar cell devices. • Annealing induced properties of ZnTe:Cu interface layer are investigated for solar cells. • The ZnTe:Cu films showed crystal growth along (103) preferred orientation. • Optical band gap of ZnTe:Cu films is found in 2.10–2.74 eV range with annealing. • AFM images showed hill-like topographies and EDS patterns confirmed films deposition. • SEM images revealed spherical grains and I-V curves ensured ohmic nature.