Determining the most promising anchors for CuSCN: ab initio insights towards p-type DSSCs

Although copper thiocyanate (CuSCN) shows potential as a substrate for p-type dye sensitised solar cells, its interaction with organic anchoring groups remains largely unexplored. In this ab initio study, we provide atomistic insight into how CuSCN surfaces interact with a series of nitrogen-based (pyridine, aniline, phenanthroline, benzenediamine) and sulfur-based (thiophenol, thiophenoxide, thiocatechol) anchoring groups. We profile several low-index surfaces, including both polar and nonpolar cleavages, to determine their stabilities and electronic structures. In screening these surfaces for the most favourable adsorption modes and binding sites for organic anchors, we found that adsorption is chiefly driven by the propensity of surface copper atoms to restore a tetrahedronal coordination environment. We show that the majority of the tested anchors, even the bidentate structures, exhibit low binding energies on CuSCN, which illustrates how chemical intuition may be misleading for identifying the ideal anchors on the basis of nucleophilicity and denticity alone. By pinpointing the causes of modest adsorption energies, we present hints as to how adsorption strength and alignment of the organic-inorganic states can be improved on CuSCN.