Defects in black zirconia responsible for solar energy harvesting

Abstract

Although metal oxides have been employed in the field of light-energy conversion, their wide band gaps limited the utilization of solar energy. Recently, several methods have been proposed to tune the band gap of metal oxides by implanting crystal defects and thus improving the light absorption performance. However, the enhancement mechanism of light absorption induced by crystal defects is lacking comprehensive atomic-scale insight. Herein, black zirconia (ZrO₂), a type of defective metal oxide modified from ZrO₂ with a wide band gap, was thoroughly investigated by combining first-principles calculations and experimental verification. The calculation results confirm that oxygen vacancies (V_O) are the most likely defects generated in ZrO₂ owing to their low formation energy in all chemical environments, which are widely accepted to elucidate the darkening phenomenon of defective ZrO₂. Of note, we demonstrated for the first time that it is facile to generate interstitial zirconium (I_Zr) defects, which also can decrease the band gap and enhance the light absorption performance of ZrO₂, under V_O-rich conditions. Moreover, the I_Zr defects in ZrO₂ can promote the absorption of long-wavelength visible light and near-infrared light, while the V_O defects tend to facilitate the absorption of short-wavelength visible light. Therefore, the formation of V_O and I_Zr defects provides an efficient approach to enhance the light absorption of ZrO₂.