Time evolution to CdCl2 treatment on Cd-based solar cell devices fabricated by vapor evaporation

Abstract

In this work, a study on the time evolution to post-CdCl2 heat treatment on the Cd-based solar cell devices is undertaken where the devices were fabricated employing vapor evaporation method and analyzed by different measurement tools like light current-voltage, capacitance-voltage and quantum efficiency to investigate the performance along with surface morphology. CdTe-based solar devices were analyzed with the application of post-CdCl2 heat treatment by varying annealing time. CdS layer was used as window layer with device structures ITO/CdS/CdTe/CdCl2/Cu-Au and FTO/CdS/CdZnTe/Cu-Au where in later structure, CdZnTe layer was used as absorber layer before the front contact to avoid open circuit voltage loss in the superstrate structure as CdTe-based thin film solar cells are suffered by the problem of suitable metal contact owing to difference between work function of used metal and position of valance band of CdTe layer. The performance characteristics reveal that the maximum efficiency for CdTe thin film solar cells is 7.13% with post-CdCl2 heat treatment of 75min while 8.11% efficiency is recorded for CdZnTe solar cell device which is low as compared to the reported value but relatively good as in the present devices, the material consumption of absorber layer is quite low i.e. only 1.1μm instead of typical thickness of 4–5μm as well as low cost fabrication technique is used. The experimental results reveal that the treatment duration of post-CdCl2 plays an important role to enhance the performance of CdTe solar devices at lower thickness of the absorber layer.