Noticeable effect of coating temperature on Co3O4 thin films developed through low-cost nebulizer spray pyrolysis for photo-sensing applications

Abstract

Cobalt oxide thin films are synthesized at various temperatures from 275 to 375 °C using a nebulizer spray pyrolysis technique. Different characterization approaches are used to investigate the effects of coating temperature on the characteristics of coated thin films. The deposited films have a cubic structure with a preferred orientation along the (111) direction. Field Emission Scanning Electron Microscope (FESEM) reveals the grain size of the samples as the coating temperature rises. The energy dispersive x-ray analysis (EDS) spectra confirm that the growing film is primarily made up of Co and O. The optical absorption spectra show an increase in absorption with increasing coating temperature. The band-gap energy values are lowered by 2.12, 2.10, 2.09, 2.01, and 2.05 eV with respect to the coating temperatures of 275, 300, 325, 350, and 375 °C, respectively. The observed photoluminescence(PL) spectra exhibit the band edge and defect-based emissions for all the films. Studies of current (vs) voltage revealed ohmic nature up to 350 °C coating temperature. At coating temperature 375 °C hysteretic behavior of film is observed because of the increasing number of vacancies and defective sites, which act as trap of charge carriers. The photo-detection capabilities of these coated Co3O4 thin films were investigated using optoelectronic characteristics. The optical and electrical properties have also been controlled by the fusing temperature. The Co3O4 (350 °C) produce high photocurrent (8.84 × 10−7A), external quantum efficiency (11.6%), detectivity (3.5 × 109 Jones), responsivity (4.99 × 10−2 AW−1) and has the shortest rise/decay time among the constructed photo-detectors. These findings show the tuning of the properties of Co3O4 by optimizing the coating temperature for the fabrication of effective photo-detectors.