High-efficiency CIGSSe solar cells enabled via solution-processed ZnO, TiO2, and SnO2 nanoparticle window layers

Abstract

An intrinsic zinc oxide (i-ZnO) thin film serves as a common transparent window layer in high-performance Cu(In,Ga)(S,Se)₂ (CIGSSe) thin film solar cells. However, its conventional deposition via radio-frequency magnetron sputtering increases fabrication costs and limits large-scale industrial production, owing to the complexity of vacuum-based deposition techniques. Developing low-cost, highly transparent, and easily fabricated alternative window layers is therefore crucial for advancing the commercialization of CIGSSe solar cells. Solution-processed metal oxide nanoparticle thin films, such as ZnO, TiO₂, and SnO₂, offer excellent optical transmittance and reduced fabrication cost compared to sputtered i-ZnO. In this study, we systematically investigate the effects of metal oxide nanoparticle concentrations and annealing conditions on the photovoltaic performance of CIGSSe devices. Optimal concentrations are identified as 30 mg mL⁻¹ for ZnO, 15 mg mL⁻¹ for TiO₂, and 30 mg mL⁻¹ for SnO₂. Under these conditions, all three nanoparticle films exhibit over 90% transmittance, enabling champion power conversion efficiencies of 10.22%, 10.25%, and 11.08%, respectively. Furthermore, the devices incorporating these nanoparticle window layers demonstrate excellent stability. This work provides a viable strategy for developing high-performance and cost-effective CIGSSe thin film solar cells through solution-processed metal oxide nanoparticle window layers.