Systematic in situ Raman microdroplet spectroelectrochemical (Raman-μSEC) characterization of copper (I) thiocyanate (CuSCN) prepared using electrodeposition from aqueous solution on various substrates (carbon-based, F-doped SnO2) is presented. CuSCN is a promising solid p-type inorganic semiconductor used in perovskite solar cells as a hole-transporting material. SEM characterization reveals that the CuSCN layers are homogenous with a thickness of ca. 550 nm. Raman spectra of dry CuSCN layers show that the SCN- ion is predominantly bonded in the thiocyanate resonant form to copper through its S-end (Cu-S-C≡N). The double-layer capacitance of the CuSCN layers ranges from 0.3 mF/cm2 on the boron-doped diamond to 0.8 mF/cm2 on a glass-like carbon. In situ Raman-μSEC shows that, independently of the substrate type, all Raman vibrations from CuSCN and the substrate completely vanish in the potential range from 0 to -0.3 V vs. Ag/AgCl, caused by the formation of a passivation layer. At positive potentials (+0.5 V vs. Ag/AgCl), the bands corresponding to the CuSCN vibrations change their intensities compared to those in the as-prepared, dry layers. The changes concern mainly the Cu-SCN form, showing the dependence of the related vibrations on the substrate type and thus on the local environment modifying the delocalization on the Cu-S bond.
Keywords: CuSCN; carbon; hole-transport material; in situ Raman spectroelectrochemistry.