Comparison of the physico-chemical properties of NiO thin films deposited by chemical bath deposition and by spray pyrolysis

Abstract Nickel oxide (NiO) thin films were obtained by two methods: chemical bath deposition (CBD) and spray pyrolysis. During the CBD deposition process, the bath was heated at 100 °C. The CBD as-deposited films corresponded to 3Ni(OH) 2 ·2H 2 O. After an annealing time of 96 h at 350 °C, they became NiO. For the spray deposition, the nickel chloride hexahydrate (NiCl 2 ·6H 2 O) was chosen as precursor, the glass substrates were heated at 350 °C. All the films were p-type semiconductors with a band gap of 3.5 eV. The X-ray diffraction diagrams revealed that all the films are crystallized in the cubic NiO phase with the expected value for the lattice parameters. Nevertheless, the orientation and the size of the grains depend on the deposition method. The films are oriented along the (1 1 1) plane in the case of spray, while they are oriented in the (1 1 1) and (2 0 0) planes in the case of CBD. The electron probe microanalysis and the X-ray photoelectron spectroscopy was used to measure the composition of the films. The X-ray photoelectron spectroscopy shows the presence of hydroxyl groups at the surface of the films, while the electron probe microanalysis shows that the films are stoichiometric in the bulk. The scanning electron microscope microphotographs show that all the films exhibit a rough surface with a presence of microstructural features in the case of CBD films. These properties are desired for an eventual application in microcrystalline solar cells.