Applied bias photon-to-current conversion efficiency of ZnO enhanced by hybridization with reduced graphene oxide

The role of reduced graphene oxide (rGO) in the enhancement of photo-conversion efficiency of ZnO films for photoelectrochemical (PEC) water-splitting applications was analyzed. ZnO and rGO-hybridized ZnO (rGO/ZnO) films were prepared via a two-step electrochemical deposition method followed by annealing at 300 °C under argon gas flow. The physical, optical and electrochemical properties of the films were characterized to identify the effect of rGO-hybridization on the applied bias photon-to-current efficiency (ABPE) of ZnO. Scanning electron microscopy and X-ray diffraction indicated the formation of vertically-aligned, wurtzite-phase ZnO nanorods. Diffuse-reflectance UV–visible spectroscopy indicated that rGO-hybridization was able to increase the light absorption range of the rGO/ZnO film. UPS analysis showed that hybridization with rGO increased the band gap of ZnO (3.56 eV) to 3.63 eV for rGO/ZnO sample, which may be attributed to the Burstein–Moss effect. Photoluminescence (PL) spectra disclosed that rGO-hybridization suppressed electron-hole recombination due to crystal defects. Linear sweep voltammetry of the prepared thin films showed photocurrent density of 1.0 and 1.8 mA/cm² for ZnO and rGO/ZnO at +0.7 V, which corresponded to an ABPE of 0.55% and 0.95%, respectively. Thus, this report highlighted the multi-faceted role of rGO-hybridization in the enhancement of ZnO photo-conversion efficiency.