An efficient organic solvent-free solution-processing strategy for high-mobility metal chalcogenide film growth

One of the primary challenges for high-quality metal chalcogenide film growth by a chemical solution approach is to avoid the use of volatile/hazardous organic solvents during the fabrication processes. Herein, we demonstrate an organic solvent-free solution processing method which has the ability to enable growth of a diverse range of metal chalcogenide films. The processing solution is prepared by combining the required metal ions with non-volatile and non-flammable ionic liquid precursor solutions. These stable and homogeneous solutions can form a variety of high-quality and uniform metal chalcogenide films. Due to the facile and instant control of the stoichiometry used in this method, the band gap of multi-element compound semiconductors, for example quinary Cu2ZnSn(S,Se)4, can be easily tuned from 1.01 eV of Cu2ZnSnSe4 to 1.52 eV of Cu2ZnSnS4. The resulting film also shows high hole mobility with a maximum of 56.9 cm2 V−1 s−1 for a carrier concentration of 3.24 × 1016 cm−3 at room temperature. Cu2ZnSnS4-based solar cells displayed an efficiency of 5.68%, which is comparable to the reported efficiencies of solar cells prepared by methods involving organic solvents (5.0–6.4%).