Cosolvent approach for solution-processable electronic thin films

Lowerature solution-processable electronic materials are of considerable interest for large-area, low-cost electronics, thermoelectrics, and photovoltaics. Using a soluble precursor and suitable solvent to formulate a semiconductor ink is essential for large-area fabrication of semiconductor thin films. To date, it has been shown that hydrazine can be used as a versatile solvent to process a wide range of inorganic semiconductors. However, hydrazine is highly toxic and not suitable for large-scale manufacturing. Here we report a binary mixed solvent of amine and thiol for effective dispersion and dissolution of a large number of inorganic semiconductors including Cu₂S, Cu₂Se, In₂S₃, In₂Se₃, CdS, SnSe, and others. The mixed solvent is significantly less toxic and safer than hydrazine, while at the same time offering the comparable capability of formulating diverse semiconductor ink with a concentration as high as >200 mg/mL. We further show that such ink material can be readily processed into high-performance semiconducting thin films (Cu₂S and Cu₂Se) with the highest roomerature conductivity among solution-based materials. Furthermore, we show that complex semiconductor alloys with tunable band gaps, such as CuIn(S_xSe_1-x)₂ (0 ≤ x ≤ 1), can also be readily prepared by simply mixing Cu₂S, Cu₂Se, In₂S₃, and In₂Se₃ ink solutions in a proper ratio. Our study outlines a general strategy for the formulation of inorganic semiconductor ink for lowerature processing of large-area electronic thin films on diverse substrates and can greatly impact diverse areas including flexible electronics, thermoelectrics, and photovoltaics.