Organic-acid texturing of transparent electrodes toward broadband light trapping in thin-film solar cells

Regardless of the great importance of light trapping towards the breakthrough in the saturated photoconversion efficiencies of Si thin-film solar cells, much research on the surface texturing of transparent conducting oxides (TCOs) has been focused more on the nanostructural control during thin film growth. Herein, an organic acid for the surface texturing of ZnO:Al is introduced as an alternative to the conventional HCl etchant, making more efficient light scattering by TCO. The texturing behavior by oxalic acid is investigated in terms of vertical roughness and lateral correlation length, and a mass-transport model is developed to explain the etching evolution mechanisms. Texturing with oxalic acid results in superior light-scattering performance (by ~8% more haze at λ=1000 nm) with maintaining the transparency and resistance, compared to the etching with HCl. This fascinating behavior is explained by utilizing the light-scattering haze model with the extracted two surface parameters. Significantly, this straightforward and reproducible texturing tactic extends tunability for the desirable TCO morphology, enabling efficient light trapping, and therefore appears potentially applicable for the large-scale photovoltaic devices in industry.