Here we report the first theoretical characterization of the interface between the CuGaO
2
delafossite oxide and the carboxylic (–COOH) and phosphonic acid (–PO
3
H
2
) anchoring groups. The promising use of delafossites as effective alternative to nickel oxide in p-type DSSC is still limited by practical difficulties in sensitizing the delafossite surface. Thus, this work provides atomistic insights on the structure and energetics of all the possible interactions between the anchoring functional groups and the CuGaO
2
surface species, including the effects of the Mg doping and of the solvent medium. Our results highlight the presence of a strong selectivity toward the monodentate binding mode on surface Ga atoms for both the carboxylic and phosphonic acid groups. Since the binding modes have a strong influence on the hole injection thermodynamics, these findings have direct implications for further development of delafossite based p-type DSSCs.
CuMO2 delafossites (M = Al, Ga, and Cr) are p-type semiconductor oxides that have been recently proposed as the electrode in p-type dye-sensitized solar cells (p-DSSC) which is an alternative to the standard, low-performing nickel oxide. To assess this potential application of delafossites, we report here a DFT-based investigation of the structural and electronic properties of CuAlO2, CuGaO2 and CuCrO2. In particular, we address the role of Mg doping to obtain the p-type semiconducting character: the substitution of an M3+ cation with Mg2+ is easier with Ga than with Al and Cr, and, in all cases, the hole introduced by Mg2+ leads to the formation of Cu2+ species. Moreover, we address surface electronic features in order to characterize the most exposed delafossite surface termination and, more importantly, to predict the valence band maximum energy value, which determines the p-DSSC open circuit potential. From analysis of all our results, CuGaO2 emerges as the most promising system that can boost the development of new photocathodes for p-DSSCs.
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