The theoretical investigation on the 4-(4-phenyl-4-α-naphthylbutadieny)-triphenylamine derivatives as hole transporting materials for perovskite-type solar cells

The electronic structures, optical properties and hole mobilities of 4-(4-phenyl-4- α-naphthylbutadieny)-triphenylamine and its five derivatives are investigated by density functional theory (DFT). The results show that the highest occupied molecular orbital (HOMO) of all molecules is almost fully delocalized throughout the whole molecule, and the substituents -N(CH₃)₂ and -C₆H₅ denoted as molecules 6 and 2, respectively, have the largest contribution to the HOMO, which is favorable for hole transfer integral and hole mobility. Spectrum analysis indicates that all molecules have large Stokes shifts based on absorption and emission spectra. In addition, it is found that the hole reorganization energy of all molecules is about 0.5 times compared to that of electrons, which implies that hole mobility is bigger than electron mobility. On the basis of predicted packing motifs, the hole mobilities (u) of all molecules are also obtained. The largest hole mobility of molecule 2 (0.1063 cm² V^-1s^-1) is found to be higher than that of other molecules due to the face-to-face stacking mode, which suggests that -C₆H₅ is a good substituent group for improving hole mobility compared to other electron releasing groups. We hope that our results will be helpful for the further rational molecular design and synthesis of novel hole transport materials (HTMs) for high performance perovskite-type solar cells.