Solution Processed Fabrication of Se-Te Alloy Thin Films for Application in PV Devices

In this work, we report the first-ever fabrication of solutionprocessed Se-Te alloy thin films for photovoltaic applications using an amine- thiol solvent system. By controlling the relative quantity of Se and Te in ethylenediamine-ethanethiol (EN-ET) solution mixtures, films with different Se/ Te ratios were fabricated at temperatures as low as 200 degrees C with phase-pure material synthesis and uniform homogenous alloying. These composition variations then successfully demonstrated band gap variation from 1.80 eV for pure Se to 1.18 eV for a film with 60% Se and 40% Te that closely matches the theoretical values calculated from Vegard's law for these materials. Using the evaporation process, the isolation of chalcogen complexes from the EN-ET solution was performed, which was followed by the addition of foreign solvents like dimethyl sulfoxide, dimethyl formamide, and ethanolamine, which enabled the fabrication of better quality films using the spin coating process, minimizing the porosity and increasing the uniformity of the film. A preliminary device fabricated from these films showed diode characteristics with encouraging photovoltaic performance (a power conversion efficiency of 1.11%) that demands further optimization with film fabrication, selection of device architecture, and detailed defect analysis for this material.