Numerical and Experimental Investigation of AZO Thin Films for Enhanced Photovoltaic Performance in ZnO/Si, ZnO/GaAs, and ZnO/CdTe Heterojunction Solar Cells

Abstract

The development of solar cells that use less silicon while maintaining high photovoltaic efficiencies is a major goal in the photovoltaic field. This study presents a systematic comparison of the photovoltaic performance of three structures: n-ZnO/p-Si, n-ZnO/p-GaAs, and n-ZnO/p-CdTe using two-dimensional numerical simulations. The impact of donor concentration and thickness of the ZnO layer on the performance of the devices is examined, revealing optimal conversion efficiencies of 12.93% for ZnO/p-Si, 21.24% for n-ZnO/p-GaAs, and 18.91% for n-ZnO/p-CdTe. Experimentally, undoped ZnO and aluminum-doped ZnO (AZO) layers were fabricated via the spin-coating technique. X-ray diffraction confirmed the hexagonal wurtzite structure in both ZnO and AZO films, while UV-Visible spectroscopy revealed a slight band gap increase due to Al doping. Hall-effect measurements showed a significant enhancement in electrical properties, with resistivity dropping from \(32.13 \Omega \text{cm}\) (undoped ZnO) to \(1.20\Omega \text{cm}\) (AZO numerical simulations of the three heterojunction structures, incorporating the spin-coated ZnO and AZO layers, revealed a notable enhancement in photovoltaic performance when AZO was used instead of undoped ZnO. Among the studied structures, the AZO/p-GaAs and AZO/p-CdTe heterojunctions exhibited higher conversion efficiencies than the conventional AZO/p-Si structure, showcasing their potential for advancing solar cell technology.