Photoelectric Properties of SZO/p-GaAs Heterojunction Solar Cells

In this work, we have prepared Sn-doped zinc oxide (SZO) thin films in the range of Sn concentrations of 0–6 wt.% using the spin coating technique to integrate them as emitters in the SZO/p-GaAs photovoltaic structure. The films exhibited a hexagonal würtzite structure highly oriented along the c-axis of the lattice. The SZO film with 3 wt.% Sn showed less strain and stress of lattice. The mean grain size and surface roughness increased with the Sn rate. Additionally, the films demonstrated high optical transmittance and low reflectance in the visible range; also, the films recorded a slight decrease in the optical band gap and refractive index versus the Sn content. Photoluminescence spectra revealed a decrease in ZnO intrinsic defects with Sn rate. The electrical resistivity of the films is strongly dominated by the charge carrier mobility. The SZO film with 3 wt.% Sn recorded the minimal resistivity. Subsequently, numerical simulation showed that the electrical properties of the SZO emitter strongly limit the photoelectric performance of the SZO/p-GaAs structure. The conversion efficiency increased from 0.204% to 14.65% for a high mobility of 25 cm² V⁻¹ s⁻¹ and a carrier density of 5 × 10¹⁹ cm⁻³ in the SZO emitter zone.