Phase transition, structural, optical and thermoelectric properties of spin coated CuxS thin films

Copper sulphide (CuxS) thin films were deposited by the spin coating method using copper acetate (Cu₂(CH₃COO)₄) and thiourea (CH₄N₂S) as precursors. This simple technique was shown to produce thin films with high quality in terms of tunable stoichiometry and physical properties. In fact, the room temperature structural, optical and thermoelectric properties were studied. It is observed that the annealing during 1 h at 250 °C and 300 °C results in the transition from the covellite (CuS) to the chalcocite (Cu2S) and djurleite (Cu1.95S) phases, respectively. Optical measurements show the formation of absorbing films in the visible range with a transmittance lower than 50 % for all phases. The covellite phase is found to be thermoelectrically interesting with a power factor of 12.3 μWK−2m−1, while the conductivity of the djurleite phase (281.7 Ω−1cm−1) needs to be improved to match its high Seebeck coefficient (21.3 μVK−1).