Morphological, optical and electrical properties of GaSe9 films and its application in photovoltaic devices

Abstract

We report on the characterization of crystalline GaSe9 thin films produced by thermal evaporation onto fluorine doped tin oxide (FTO) transparent electrode substrate, and its further application in photovoltaic devices. The physical properties are studied in order to understand the implications of gallium addition to the Se alloy. Hexagonal structure of the crystalline films after thermal annealing is confirmed by X-ray diffraction, whereas scanning electron microscopy images indicate improved morphology in GaSe9 films, in comparison to Se films. Photoelectrical properties of the devices are studied by current density–voltage, capacitance–voltage and impedance spectroscopy measurements. GaSe9 based devices show average power conversion efficiency of 1.37 %, under 100 mW/cm2 AM 1.5 irradiance, in a simple FTO/GaSe9/Au structure. It means an increase of 40 % with respect to Se devices under the same structure. Additional improvements are related with the built-in potential, charge carrier concentration and depletion width, which are derived by the Schottky–Mott relationship. Finally, from impedance spectroscopy measurements, an increase in the recombination time and a faster charge extraction in GaSe9-based devices are observed.