The promise of solution-processed Fe.sub.2GeS.sub.4 thin films in iron chalcogenide photovoltaics

The olivine Fe.sub.2GeS.sub.4, featuring non-toxic elements, cost-effective synthesis, and suitable optoelectronic properties, recently emerged as a promising light-absorbing candidate. Fe.sub.2GeS.sub.4 precursor powders obtained via a simple solution-based process were converted to highly crystalline Fe.sub.2GeS.sub.4 powders upon a thermal treatment in controlled atmosphere. Thin films fabricated by dip coating in the Fe.sub.2GeS.sub.4 precursor dispersion and subjected to the same thermal treatment render high-purity Fe.sub.2GeS.sub.4 thin films with a band gap of 1.4 eV, measured by room-temperature photoluminescence. Using Fe.sub.2GeS.sub.4 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 Fe.sub.2GeS.sub.4 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 Fe.sub.2GeS.sub.4.