Growth mechanisms of CuSCN films electrodeposited on ITO in EDTA-chelated copper(II) and KSCN aqueous solution

Electrodeposition of β-CuSCN films was investigated on transparent conducting ITO substrates in an aqueous electrolyte containing EDTA-chelated Cu(II) and KSCN. It has been observed that the instability of CuSO4 and KSCN aqueous solution without EDTA is due to the formation of Cu(SCN)2 precipitation, which can transform into CuSCN and (SCN)x at room temperature. Research results illuminate that the deposited film at −0.5 V versus Ag/AgClsat at 298 K is uniform and dense and composed of nanocrystals. The film is p-type with stoichiometric excess of SCN and a direct transition gap of 3.7 eV. Deposition mechanisms of CuSCN films at varied temperatures are studied based on the proposed energetic model. At or below room temperature, the electron quantum tunnel through deposition layer is predominant at the very beginning. However, the growth is limited when the thickness of CuSCN film reaches the size comparable to the diffusion length of electrons. Above room temperature, the thermal activation of surface states plays an important role in the continuous growth of large crystals through holes transport in the valence band. The calculated activation energy for crystal growth is 0.5 eV.