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

Designed with a steric twisted, π-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 π-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 π-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 × 10−1 cm2 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.