Investigation of n-ZnO/p-GaAs Heterojunction Solar Cell Using Two-Dimensional Numerical Simulation

The n-ZnO/p-GaAs heterojunction is a promising structure to reach good conversion efficiency owing to the important optical and electrical properties of both zinc oxide (ZnO) and gallium arsenide (GaAs) semiconductors. In this work, the n-ZnO/p-GaAs heterojunction solar cell was studied to estimate the best photovoltaic parameters of the structure. For that, the effects of thickness and charge carrier concentration of both n-ZnO and p-GaAs absorber on the photovoltaic performance were investigated under standard illumination conditions (AM1.5, 100 mW/cm(2)). A two-dimensional numerical simulation was carried out using Atlas Silvaco software. An optimal p-GaAs thickness of 100 & mu;m was found, from which no significant change in the conversion efficiency was noted. A high sensitivity of the conversion efficiency by varying the ZnO donor concentration was observed, while the presence of an optimal GaAs acceptor density was revealed. Additionally, an optimal ZnO thickness of 200 nm was shown. The n-ZnO/p-GaAs cell showed a predicted best conversion efficiency of 21.21%. Furthermore, it was revealed that reducing the thickness of the GaAs absorber layer to 2 & mu;m allowed for a significant conversion efficiency of 16.19%, with an optimal GaAs acceptor concentration of 4 x 10(18) cm(- 3).