Ab Initio Gga+U and Experimental Study of the Wurtzite Structure of ZnO for Dye-Sensitized Solar Cells Application

Abstract

Zinc oxide (ZnO) is an extensively utilized, versatile compound implemented in a diverse scope of technological applications. In dye-sensitized solar cells (DSSCs), the attainable nanostructures, inherent transparency and tunable electronic properties of ZnO can be integrated to confer high level device properties. ZnO is a complex compound with substantial and intricate defect chemistry and its properties are exceptionally sensitive to the functional utilized in the computing and experimental processes. Consequently, engineering of the band edges in Wurtzite ZnO (W-ZnO) for DSSCs application has not yet been exhausted. The W-ZnO was synthesized using sol-gel method while the computations were performed using density functional theory (DFT) as implemented in the Quantum ESPRESSO code. The generalized gradient approximation with Perdew-Burke-Ernzerhof was utilized as the exchange correlation functional. Investigations of the structural, electronic and optical properties of W-ZnO were carried out using both computational and experimental techniques. In the experimental analysis, the influence of growth temperature on ZnO was investigated, whereas in the computational study, the impact of varying the Hubbard U parameter on pure ZnO was examined. The structural properties of the materials have been found to be consistent with previous observations in literature with a slight decrease in lattice parameters in the DFT+U calculations. W-ZnO was observed to display a direct band gap at gamma. The energy band gaps of, 0.79 eV, 1.45 eV, 3.19 and 3.33 eV in the standard DFT, DFT + Ud, DFT+Ud +Up calculations and experimental values were obtained respectively. Generally, W-ZnO was found to have low absorption ability and high transmittance in the visible spectrum which were in close correlation with the experimental values obtained which therefore make them suitable candidates for DSSCs application.