The promise of solution-processed Fe₂GeS₄ thin films in iron chalcogenide photovoltaics

The olivine Fe₂GeS₄, featuring non-toxic elements, cost-effective synthesis, and suitable optoelectronic properties, recently emerged as a promising light-absorbing candidate. Fe₂GeS₄ precursor powders obtained via a simple solution-based process were converted to highly crystalline Fe₂GeS₄ powders upon a thermal treatment in controlled atmosphere. Thin films fabricated by dip coating in the Fe₂GeS₄ precursor dispersion and subjected to the same thermal treatment render high-purity Fe₂GeS₄ thin films with a band gap of 1.4 eV, measured by room-temperature photoluminescence. Using Fe₂GeS₄ thin films as the sole absorber in a solution-based solar cell, open-circuit voltages of 361 mV are observed, while the use of the Fe₂GeS₄ films as counter electrodes in dye-sensitized solar cell constructs enhances the overall power conversion efficiency of the cell by a factor of five. This is the first report of a photovoltaic device based on Fe₂GeS₄.