Effect of substituting donors on the hole mobility of hole transporting materials in perovskite solar cells: a DFT study

Several hole-transporting materials (HTMs) have been designed by incorporating different types of pi-conjugation group such as long chain aliphatic alkenes and condensed aromatic rings of benzene and thiophene and their derivatives on both sides between the planar core and donor of a reference HTM. Various electronic, optical, and dynamic properties have been calculated by using DFT, TDDFT, and Marcus theory. In this study, all the designed HTMs show a lower HOMO energy level and match well with the perovskite absorbers. Inserting condensed rings results in better hole mobility compared to aliphatic double bonds. It is found that the charge transfer integral is the dominant factor which mainly influences the hole mobility in our studied HTMs. Other factors such as hole reorganization energy, hole hopping rate, and centroid distance have a minor effect on hole mobility. Thus, this study is expected to provide guidance for the design and synthesis of new HTMs with increased hole mobility. Several HTMs have been designed by adding various types of pi-conjugation group on both sides of the planar core of reference HTM, resulting that charge transfer integral is the dominant factor which mainly influence the hole mobility.