Optoelectronic and solar cell applications of ZnO nanostructures

ZnO has risen as a vital material for electron transportation in a greater number of solar cells based on nanostructures because of its abundance, nontoxicity, and high electron mobility. We performed first principle calculations on structural, optical, and electronic properties of 2D zinc oxide monolayer and bilayer honeycomb structures. Our work includes study of wurtzite, zinc blende, and tetragonal bulk structures revealing dimensionality effects. Calculated electronic band gaps affirm the band gap to be direct for all structures, having range (0.561-0.761 eV) using GGA and (0.766-0.910 eV) using LDA+U for bulk structures, while for bilayer and monolayer it is 1.419 eV (GGA), 1.413 eV (LDA+U) and 1.691 eV (GGA), 1.683 eV (LDA+U) respectively. The shrunken Zn-O bond length of monolayer predicts it to be more ionic compared to bulk structures. Moreover, the optical properties like absorption, dielectric function of all honeycomb-like structures are also analyzed. To make a comparison of ionicity of all structures Hirshfeld analysis is made to investigate charge transfer. Absorption spectra are calculated to understand the optical behavior of these systems, especially in visible portion. The absorption efficiency of ZnO was investigated as it could be a promising material for the use in solar cell. For the future, we expect that ZnO would be a potential candidate for solar cell application.