Abstract
Solar cells based on CdTe have reached a maximum practical recorded efficiency of 20.4%, which is low compared to its theoretical limit (29%). Novel concepts are required to further increase the efficiency of CdTe based solar cells. One possible approach is the graded bandgap CdZnTe solar cells. The commercial CdTe solar cells usually have thicker absorber layer. However, by using graded bandgap CdZnTe the absorber layer thickness can be reduced significantly, which eventually will reduce the cost, save processing time and energy required for fabrication. In this work, numerical simulation on graded bandgap CdZnTe solar cells is carried out by AMPS-1D software. The absorber layer of graded bandgap CdZnTe solar cells are optimized by two approaches (A and B), where each approach has four optimized structures. Finally, one optimized cell structure is selected for each approach. The results of the best cells for approach A and B are Voc= 0.884 Volt, Jsc=32.074 mA/cm(2), FF= 0.801, Efficiency = 20.66% and Voc= 0.887 Volt, Jsc= 32.021 mA/cm(2), FF= 0.788, Efficiency = 20.35%, respectively. These cells have good stability at higher operating temperature, which are -0.043%/degrees C for the best cell of approach A and 0.038%/degrees C for the best cell of approach B. The best cells are also analyzed in terms of window layer thicknesses. It is found that by increasing the thickness of CdS window layer the efficiency decreases due to reduction of Jsc. Additionally, it is found that efficiency further increases for the insertion of a ZnO buffer layer.