Molecular design of dibenzo[g,p]chrysene-based hole-transporting materials for perovskite solar cells: A theoretical study

Designed with a steric twisted, pi-conjugated dibenzochrysene (DBC) core and arylamine-based electron-donating side arms, four small molecules as hole-transporting materials (HTMs) are simulated with density functional theory and Marcus theory of electron transfer. Our results show that, adding the fluorene moiety in auxiliary side arms and extending the pi-conjugated structure can make the highest occupied molecular orbital (HOMO) energy levels down-shifted. By tailoring of electron-donating side arms, the HOMO levels of designed HTMs range from-4.95 to-5.24 eV, which affords a chance for the interfacial energy regulation. Meanwhile, we also find that the suitable extension of pi-conjugated side arms and the accessorial sulfur-sulfur interaction may be beneficial for promoting the intermolecular electronic coupling. Coupled with the lower reorganization energy, the DBC-4 (7.08 x 10(-1) cm(2) v(-1) s(1)) displays the largest hole mobility. In addition, the better solubility can be expected for the DBC-4 due to the larger solvation free energy, whereas its stability may be somewhat lower. Adding thiophene unit in side arms makes the absorption spectra obviously red-shift. Overall, this work provides some useful clues for designing of high-efficient HTMs, and the DBC-4 is proposed as potential HTM.