Efficiency Enhancement of the CdS/CdTe Solar Nanostructured Cell Using Electron-Reflecting Layer

Abstract

A novel nanopillar-based n-CdS/p-CdTe solar cell with p-CdZnTe electron-reflecting layer has been proposed. The proposed structure features a p-CdZnTe electron-reflecting layer at the anode electrode side of the device. Device simulation using TCAD device simulator SILVACO has shown that the open-circuit voltage (<inline-formula> <tex-math notation= LaTeX >${V}_{oc}$ </tex-math></inline-formula>) of the device can be improved without degrading the short circuit current density (<inline-formula> <tex-math notation= LaTeX >${J}_{sc}$ </tex-math></inline-formula>) of the device. Furthermore, the effect of Zn composition in the p-CdZnTe layer has also been studied on the device performance parameters of interest such as open-circuit voltage (<inline-formula> <tex-math notation= LaTeX >${V}_{oc}$ </tex-math></inline-formula>), short circuit current density (<inline-formula> <tex-math notation= LaTeX >${J}_{sc}$ </tex-math></inline-formula>), fill factor (FF), and solar cell conversion efficiency (<inline-formula> <tex-math notation= LaTeX >$\\eta $ </tex-math></inline-formula>). A detailed analysis has shown that increasing the Zn composition beyond 40% limits the FF due to the increase in the valence band offset energy <inline-formula> <tex-math notation= LaTeX >$\\varDelta {E}_{v}$ </tex-math></inline-formula>, on the other hand, lowering Zn composition below 40% decreases the much-desired conduction band offset energy (<inline-formula> <tex-math notation= LaTeX >$\\varDelta {E}_{c}$ </tex-math></inline-formula>) value. The best tradeoff relationship between the <inline-formula> <tex-math notation= LaTeX >${V}_{oc}$ </tex-math></inline-formula> and FF has been achieved for the Zn composition of 40% in the p-CdZnTe layer. At this composition of Zn, the <inline-formula> <tex-math notation= LaTeX >${V}_{oc}$ </tex-math></inline-formula>, FF, and solar cell <inline-formula> <tex-math notation= LaTeX >$\\eta $ </tex-math></inline-formula> of the device seem to be improved by 33%, 21%, and 61% respectively.