Efficiency improvement of CdZnTe solar cell by modification of interface layer

Solar conversion efficiency of graded Cd_1−x Zn _x Te solar cells is investigated numerically in this work. It is found that the efficiency can be improved if a p-Cd_0.6Zn_0.4Te layer is added to the basic n-ZnO/n-CdS/p-CdTe structure. On the other hand, there is a sharp conduction band offset at the interface of the CdTe and p-Cd_0.6Zn_0.4Te layer that affects the cell performance. At the next step, in order to remove the discontinuity at the conduction band between p-CdTe and p-Cd_0.6Zn_0.4Te, we have replaced the Cd_1−x Zn _x Te with a graded region where the Cd_1−x Zn _x Te layer is divided into several individual thinner layers. As a result, the electron (minority carrier) collection at the hetero-interface improves, duo to the establishment of an extra electric field across the graded region, leading to an increase in the solar conversion efficiency. The number of layers and doping concentration of the graded region plays an important role in the performance of the cell. Finally, it had been found that the ZnO/CdS/CdTe/Cd_1−x Zn _x Te/p-Cd_0.6Zn_0.4Te structure in which the Cd_1−x Zn _x Te region consists of 25 thin layers with 10¹⁸ cm⁻³ doping concentration will have an efficiency ≈1 % higher than that of the ungraded ZnO/CdS/CdTe structure.