Evidence of trapping levels and photoelectric properties of Cu₃BiS₃ thin films

Voltage and Cu/Bi ratio mass dependence of photocurrent was studied in Cu₃BiS₃ thin films prepared by co-evaporation technique. The intensity dependence of steady state photocurrent (I_ph) follows a power law with intensity (F), I_ph ∝ F^γ where the power γ is in the range between 0.5 and 1.0, which suggests monomolecular recombination process. Photocurrent signal was found to be decaying as a function of both applied voltage and intensity, initially decreasing at considerably fast rates and later at slower ones due to the continuos distribution of defect states. Additionally, the differential life time constants were calculated. Measurements of temperature effect on conductivity (from 100 K to 450 K) were carried out. It was found that at temperatures greater than 350 K, the conductivity is predominantly affected by transport of free carriers in extended states of the conduction band, whereas in the range of temperatures below 250 K, the conductivity is dominated by the VRH (Variable Range Hopping) transport mechanism.