Texture etched ZnO:Al coated glass substrates for silicon based thin film solar cells

Abstract

ZnO:Al films were r.f.- and d.c.-magnetron sputtered on glass substrates from ceramic (ZnO:Al2O3) and metallic (Zn:Al) targets, respectively. The initially smooth films exhibit high transparencies (T≥83% for visible light including all reflection losses) and excellent electrical properties (ρ=2.7–6×10−4 Ω cm). Depending on their structural properties these films develop different surface textures upon post deposition etching in diluted HCl. The light scattering properties of suitable films can be controlled over a wide range simply by varying the etching time. Moreover, the electrical properties are not affected by the etching process. Thus, within certain limits a separate optimization of the electro-optical and light scattering properties is possible. Amorphous silicon (a-Si:H) based solar cells prepared on these new texture etched ZnO-substrates show high quantum efficiencies in the long wavelength range demonstrating an effective light trapping. First a-Si/a-Si stacked solar cells were realized with initial efficiencies exceeding 10%.