Optoelectronic properties and low temperature thermoelectric effects were studied on polycrystalline thin films of ternary chalcopyrite ordered vacancy compound (OVC) n‐CuIn3Se5. The thin films prepared by three source vacuum co‐evaporation method were preliminarily characterized structurally, morphologically, and compositionally by X‐ray diffraction (XRD), atomic force microscopy (AFM), and X‐ray photoelectron spectroscopy (XPS), respectively. Optical and optoelectronic measurements were done to obtain the band gap, carrier concentration, and photosensitivity of the materials. Thermopower dependence on temperature exhibited a non‐degenerate semiconductivity, establishing Boltzmann statistics relation between carrier density and Fermi level in the films. While ionized impurity scattering has been detected near room temperature, an enhanced negative thermopower due to contribution from phonon drag has been noticed toward lower temperature in the films. Thermopower together with Hall coefficient and conductivity measurements permitted the correlation of density of states, carrier concentration, drift velocity, and the effective mass of the carriers with the conductivity of the films.

Polycrystalline thin films of the ordered vacancy compound AgGa 3 Se 5 were prepared by a multisource vacuum coevaporation technique at a substrate temperature of 623 K. X-ray diffraction and atomic force microscopy in conjunction with energy-dispersive analysis of X-rays and X-ray photoelectron spectroscopy were used for the structural, morphological, and compositional characterization. The distortion parameter and the anion displacement deduced from the X-ray diffraction data using the CTB plus h ¼ h tet rule were used for obtaining the anion-cation bond lengths. The compound manifested a slight increase in the nonideal anion displacement compared to AgGaSe 2 . The films with ternary chalcopyrite structure were found to possess an enhanced direct allowed bandgap of $1.8 eV compared to that in AgGaSe 2 indicative of the slightly reduced p-d interband repulsion due to the periodic introduction of silver vacancies. The electrical resistivity was assessed to be of the order of 10 À1 V m with n-type conductivity and the films exhibited good photosensitivity. An unusual increase in Seebeck coefficient was manifested in the low-temperature range 4-330 K with negligible phonon drag toward the very low and room temperature regime.

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