At present most of II-VI semiconductor based solar cells use the CdTe material as an absorber film. The simulation of its performance is realized by means of various numerical modelling programs. We have modelled a solar cell based on zinc telluride (ZnTe) thin film as absorber in substitution to the CdTe material, which contains the cadmium element known by its toxicity. The performance of such photovoltaic device has been numerically simulated and the thickness of the absorber layer has been optimized to give the optimal conversion efficiency. A photovoltaic device consisting of a ZnTe layer as absorber, CdS as the buffer layer and ZnO as a window layer was modelled through Solar Cell Capacitance Simulator Software. Dark and illuminated I-V characteristics and the results for different output parameters of ZnO/CdS/ZnTe solar cell were analyzed. The effect of ZnTe absorber thickness on different main working parameters such as: open-circuit voltage V oc, short-circuit current density Jsc, fill factor FF, photovoltaic conversion efficiency η was intensely studied in order to optimize ZnTe film thickness. This study reveals that increasing the thickness of ZnTe absorber layer results in higher efficiency until a maximum value and then decreases slightly. This maximum was found to be 10% at ZnTe optimum thickness close to 2 μm.

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This work reports on modeling IB (intermediate band) solar cells based on ZnTe:O semiconductor and determination of their photovoltaic parameters using SCAPS (solar cell capacitance simulator) software. A comparative study between photovoltaic performance of ZnTe and ZnTe:O based solar cells has been carried out. It has been found that the energy conversion efficiency η, short-circuit current density J sc , EQE (external quantum efficiency) and FF (fill factor) increased with increasing oxygen doping concentration N t up to the shallow acceptor density N A and decreased when N t was higher than N A . The open circuit-voltage V oc remained constant for N t lower than the acceptor doping concentration N A and decreased for N t higher than N A . The increase of η, J sc and FF is due to the fact that IB is fully empted, so sub-bandgap photons can be absorbed by hole photoemission process from the VB (valence band) to the IB. The decrease of η, J sc , EQE and FF is attributed to overcompensation for the base doping N A making electron photoemission process from IB to the CB (conduction band) maximized. This indicates that there is a competition between oxygen doping and intrinsic acceptor defects. The optimal concentrations of oxygen and shallow acceptor carriers were found to be N t ≈ 10 15 cm -3 and N A ≈ 10 14 cm -3 . The corresponding photovoltaic parameters were η = 41.5%, J sc = 31.2 mA/cm 2 , V oc = 1.80 V and FF = 75.1%. Finally, the EQE spectra showed a blue shift of absorption edge indicating that the absorption process is extended to the sub-bandgap photons through IB.

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