Simple hybrid dithiafulvenes-triphenylamine systems as dopant-free hole-transporting materials for efficient perovskite solar cells

Two extended hybrid conjugated systems based on a triphenylamine (TPA) core with two and three peripheral 1,4-dithiafulvenes (DTF) units coded WH-2 and WH-3 as hole-transporting materials (HTMs) applied in perovskite solar cells (PSCs) are synthesized by facile one-step reaction in good yield over 75%. DTF unit as electron donor can enhance the electron donating ability and the fusion of benzenic ring of TPA with DTF unit may lead to reinforced intermolecular interactions in the solid state. In addition, WH-2 and WH-3 exhibit a pyramid shape containing partial planarity and quasi three-dimensionality features, which is also conducive to enhancing the π-π stacking of molecules in the solid state. The above-mentioned structural characteristics make the two HTMs have good hole mobilities. As a result, WH-2 and WH-3 obtained the high intrinsic hole mobilities of 4.69 × 10−4 and 2.18 × 10−3 cm2 V−1 s−1 respectively. Finally, the power conversion efficiencies (PCEs) of PSCs with WH-2 and WH-3 as cost-effective dopant-free HTMs are 15.39% and 19.22% respectively and the PCE of PSC with WH-3 is on a par with that of PSC with Li-TFSI/t-BP doped Spiro-OMeTAD (19.67%).