Photoconductivity in the ordered vacancy compound CuIn5Se8

Thin films of the ordered vacancy compound CuIn5Se8 are deposited on glass substrates by multisource co-evaporation method and photoconductivity measurements are done on the films at various temperatures from 10 up to 300 K. The two photoactive bands that are identified in the spectral response spectra of CuIn5Se8 thin films at all measured temperatures are attributed to photoactive transitions between acceptor VCu to donor InCu and valence band to conduction band transitions respectively. From the spectra, a shift in band-to-band gap from 1.36 to 1.3 eV is observed with a temperature variation from 10 to 300 K. The non-exponential long-term decay observed in the transient photoconductivity spectra suggests a deep level trap-emptying process to be associated with the decay process and the decay constants are calculated by the differential life-time concept. From the steady state photocurrent analysis, a reduction in intergrain potential barrier on illumination has been noted as one reason for increase in conductivity on illumination. X-ray photoelectron spectroscopy analysis has been done to determine the binding energies of Cu, In and Se in the compound.