Morphological and optoelectronic studies on poly-crystalline leaf-like cobalt selenide thin film synthesized using a chemical bath deposition technique

The inorganic material cobalt selenide (CoSe), in crystalline form, possesses an optimal band gap matchable to the maximum of the solar spectrum, a high optical absorption coefficient and good conductivity. These characteristics make it quite suitable for use as a photo-electrode in solar conversion devices. However, it is difficult to obtain crystalline, uniform and stoichiometric deposits by conventional methods due to the large difference in their melting points. In view of this, we present a facile, low temperature chemical bath deposition route for the synthesis of highly ordered cobalt selenide thin films. Cobalt nitrate, sodium selenosulphate and ammonia were employed for the synthesis. The films were characterized using X-ray diffraction, optical absorbance, photoluminescence, electrical conductivity, scanning electron microscopy and EDS techniques. The analysis revealed a poly-crystalline structure in a stoichiometric, cubic form with a leaf-like morphology. The size and shape of the 'leaf' structure was observed to be uniform. A band gap of 1.7 eV was observed. The room temperature photoluminescence spectra displayed a strong, symmetrical peak at 1.7 eV confirming the directness of the band gap, while the conductivity measurements confirmed the semiconducting nature of the film with a single type of conduction mechanism. As per our literature survey on the chemical synthesis, this is the first attempt for the synthesis of poly-crystalline CoSe in thin film form.