Defect-induced optical absorption in the visible range in ZnO nanowires

The optical properties of ZnO nanowires containing defects are investigated using first-principles density-functional theory incorporating the LDA+U formalism. Calculations include defects in the form of substitutional N, Zn, and O vacancies as well as $+1$ charged O vacancy. Our calculations reveal that the presence of vacancies contribute strongly to optical absorption in the visible. Furthermore, the presence of $+1$ charged O vacancy is found to result in a blueshift of the absorption peaks, reducing the number of wavelengths that can be absorbed in the visible. These findings can be a useful tool for the design of new generation of materials with improved solar radiation absorption.