Solution treatment controls charge-transfer states and energy-level alignment at hybrid CuSCN-organic interfaces

Abstract

Hybrid organic–inorganic optoelectronic devices combine the advantages of both material classes. However, efficient formation of emissive charge-transfer (CT) states at organic–inorganic interfaces is rarely observed. A notable exception is the copper thiocyanate (CuSCN)-organic interface, which might be due to the molecular and defect-rich nature of CuSCN films. We show that the treatment of CuSCN–diethyl sulfide (DES) solution by heating and/or filtration has an eminent impact on the morphology of CuSCN films and by optimizing the thin film preparation the CT-state formation at CuSCN-organic interfaces can be significantly increased. This is brought about by CuSCN–DES coordination (as evidenced by X-ray photoelectron spectroscopy) and the decrease of charge trapping states. Furthermore, the valence electronic structure was measured by ultraviolet photoelectron spectroscopy and the energy-level alignment at the interface of the CuSCN layer with the highest CT-state intensity and C₆₀ interfaces is most favorable for efficient charge transport across the interface. Overall, our insight in CT-state formation efficiency at the inorganic–organic interface paves the way for further applications of CuSCN in hybrid electronic devices.