Effect of the inclusion of galium in normal cadmium chloride treatment on electrical properties OF CdS/CdTe solar cell

Abstract

The inclusion of gallium into the well-known CdCl2 post-growth treatment shows drastic improvement in both CdTe material and electrical properties of the fully fabricated CdS/CdTe-based solar cell as compared with the regular CdCl2 treatment. The optical, morphological, compositional and electronic properties the glass/FTO/n-CdS/n-CdTe/p-CdTe were explored after post-growth treatment of glass/FTO/n-CdS/n-CdTe/p-CdTe with CdCl2 and CdCl2:Ga treatments at 430 °C for 20 min. Morphological analysis show grain growths within the ranges of (100–2000) nm and (200–2600) nm for CdCl2 and CdCl2:Ga treatments as compared with the as-deposited glass/FTO/n-CdS/n-CdTe/p-CdTe layer with grain size within the ranges of (100–250) nm. Structurally, the preferred orientation of the as-deposited CdTe remains (111)C after both CdCl2 and CdCl2:Ga treatments of glass/FTO/n-CdS/n-CdTe/p-CdTe with randomisation of crystallite orientation observed after CdCl2:Ga with an increase in the diffraction intensities of the (220)C and (311)C CdTe peaks. The multilayer structure glass/FTO/n-CdS/n-CdTe/p-CdTe utilised in this work was grown using electrodeposition technique. The glass/FTO/n-CdS/n-CdTe/p-CdTe sample was divided into three sets; the first and second sets were treated with CdCl2 and CdCl2:Ga respectively, while the third set was left as-deposited. Both the CdCl2 and CdCl2:Ga sets were heat treated in air at 430 °C for 20 min, etched to improve metal/semiconductor interface and metallised with 100 nm Au contacts. The current-voltage measurements show comparative improvements in the open-circuit voltage, short-circuit current density, fill factor and the solar cell efficiency of the CdCl2:Ga treated glass/FTO/n-CdS/n-CdTe/p-CdTe as compared with the CdCl2 treated structure. A conversion efficiency of ∼11% was achieved with the CdCl2:Ga treatment while ∼7% was achieved with the CdCl2 treatment of similar glass/FTO/n-CdS/n-CdTe/p-CdTe device structure. This observation shows that the inclusion of gallium further improves CdCl2 treatment of CdS/CdTe-based solar cell due to its unique features of improving the stoichiometry of the CdTe layer.