Role of thermal treatment on the luminescence properties of CdTe thin films for photovoltaic applications

The efficiency of CdTe based solar cells is strongly enhanced by a thermal treatment in HCF2Cl ambient. CdTe thin films deposited on CdS/ZnO/ITO/glass by Closed Space Sublimation before and after the annealing are characterised. The CdTe morphology is studied by atomic forcemicroscopy and scanning electron microscopy. In the treated films the non-homogeneous distribution of the grain size disappears, in addition an increasing of the dimensions of the grains is observed. Cathodoluminescence analyses show a remarkable difference in the spectra between the treated and untreated structures. A strong increase in the intensity of the 1.4 eV band is observed by increasing the HCF2Cl content. A model of the electronic levels inside the CdTe band gap, due to incorporation of Cl (or F) is proposed.