Optimization and performance analysis of n-ZnO/p-CdTe thin heterojunction solar cells via two-dimensional numerical simulation

Abstract

The unique properties of cadmium telluride (CdTe) and zinc oxide (ZnO) semiconductors suggest promising photovoltaic performance for n-ZnO/p-CdTe heterojunctions. In this work, two-dimensional numerical simulation was utilized to study and optimize n-ZnO/p-CdTe thin heterojunction solar cells, aiming to demonstrate the highest achievable conversion efficiency for this simple structure. The effects of CdTe acceptor concentration, CdTe thickness, ZnO thickness, ZnO band-gap, ZnO donor concentration, defect density in ZnO layer, and interface defects density on the photovoltaic performance of n-ZnO/p-CdTe heterojunction were investigated under standard illumination conditions (AM1.5, 100 mW/cm2). The results revealed significant sensitivity of the photovoltaic performance to variations in CdTe acceptor and ZnO donor concentrations. Additionally, the optimal thicknesses for CdTe and ZnO were found to be 3 µm and 250 nm, respectively. Consequently, these optimal parameters yielded the following photovoltaic parameter values: JSC = 22.73 mA/cm2, VOC = 1.056 V, FF = 85.73 %, and η = 20.57 %, for a ZnO donor concentration of 1021 cm−3 and a CdTe acceptor concentration of 1017 cm−3. The analysis of ZnO bandgap energy, adjusted through Mg doping, shown that a slight increase in efficiency occurs at a band gap of 3.75 eV, corresponding to about 20 % Mg content. However, these performances deteriorate significantly when the defect density in the ZnO layer exceeds 5 × 1015 cm−3 or when the interface defect density rises above 1012 cm−2.

Keywords

• n-ZnO/p-CdTe heterojunction
• Solar cells
• Two-dimensional simulation