For optimal functionality of photovoltaic devices, it is imperative to utilize efficient compounds characterized by outstanding optoelectronic properties. The potentiality of compounds such as ZnO is not yet exhaustively exploited. In The present investigation, we execute the ab initio studies based on density functional theory (DFT) to explore the structural, elastic, mechanical, electronic, dynamical, transport and optical properties of three phases of ZnO. Ground state properties were determined in two distinct scenarios, that is, by application of standard DFT and use of the Green functional (GW) approximation. The calculated lattice constants of 4.388 Å for C-ZnO, 3.289 Å for Wurtzite (W)-ZnO and 3.276 Å for monolayer (M)-ZnO are in agreement with other DFT findings and experimental results obtained from literature. The investigated compounds were found to be mechanically and dynamically stable at ground state, ductile and anisotropic. The optical absorption coefficient curves prove that ZnO is transparent to many solar radiations as expected in photoanode of dye sensitized solar cells (DSSCs). All structures tested displayed direct band gap at gamma point of symmetry. The optical band gap was found to increase on average by 2.33 eV when GW approximation was taken into account. Basically, the inclusion of the Green’s function (G) and the screened Coulomb interaction (W) in DFT enhances the predictions of the energy band gap and optical properties. The O-2s, Zn-3d and O-2p orbitals were found to dominate the valence band while 0-2p and Zn-4s orbitals dominated the conduction band. Generally, ZnO was found to have low absorption ability and high transmittance in the visible spectrum and therefore making it suitable candidate for DSSCs application. The monolayer ZnO demonstrated the highest electrical conductivity as desired in DSSC’s.