Effects of π-conjugation on the charge-transport properties of hole-transporting materials featuring diphenylamine-π-quinacridone for perovskite solar cells: A theoretical study

Density functional theory (DFT), time-dependent DFT, and Marcus theory were used to probe the optoelectronic and charge-transport properties of compounds obtained by inserting long-chain aliphatic alkenes or condensed aromatic rings between the planar quinacridone core and the terminal donor diphenylamine moiety of a reference hole-transporting material (HTM). Compared to the reference HTM, its newly designed derivatives showed lower-lying highest occupied molecular orbitals that were well matched in energy with the valence band maximum of a representative perovskite absorber. HTMs obtained via the insertion of condensed aromatic rings showed higher hole mobilities than those obtained via the insertion of aliphatic alkenes. Overall, hole mobility was mainly influenced by the charge-transfer integral, while other factors, such as the hole reorganization energy, hole hopping rate, and centroid distance, had only minor effects.