Annealing temperature effect on the characteristics of CdSe/ZnO nanorod heterostructures fabricated by SILAR-technique for improved photoelectrochemical cell performance

The fabrication of CdSe/ZnO nanorod heterostructures on ITO conducting glass was carried out via hydrothermal and successive ionic layer adsorption reaction (SILAR) techniques. The resulting behavior of the films was studied for potential application in photoelectrochemical cells. Fabricated films were subjected to thermal treatment (annealing) by varying the temperatures and analysed for their optical, structural characteristics, and morphological as well as elemental composition. The heterostructures showed increasing light absorbancy in the visible region (410-600 nm) as the annealing temperature rises. The bandgap energy was noticed to reduce from 3.20 eV for pure ZnO NRs, to around 2.96 eV for CdSe/ZnO NRs (not annealed), and 2.54 eV, 2.44 eV, 2.36 eV, and 2.28 eV for CdSe/ZnO NRs annealed at 200-500 degrees C. The XRD patterns revealed that the fabricated films are polycrystalline having wurtzite and cubic structures for ZnO NRAs and CdSe. The appearance of new peaks indicating the formation of CdSe/ZnO NRAs heterostructures was observed with increasing annealing temperature. The FESEM images displayed the formation of nanoparticles at the tips and walls of the nanorods. The EDX results showed that the elemental composition comprises elements including Zn, O, Cd, and Se. The PEC measurement showed a pronounced enhancement in photocurrent density compared to intrinsic ZnO NRAs. Notable enhancement was obtained in the photoelectrochemical cell (PEC) performance ascribed to the quick separation, low recombination rate, and low impedance of the photoinduced electron-hole pairs as depicted in the electrochemical impedance spectra. Possible applications of the fabricated films in photoelectrochemical cells may be suggested based on their remarkable properties and photocurrent performance.