Tetrathienopyrrole-based hole-transporting materials for highly efficient and robust perovskite solar cells

Developing coplanar π-extended backbone is essential for simultaneously achieving high hole transport capability and thermal stability for hole-transporting material (HTMs). In this work, the large coplanar tetrathienopyrrole (TTTP) building block is employed to construct two novel linear organic HTMs (WH01 and WH02). With respect to the dithieno[3,2-b:2′,3′-d]pyrrole core, the extended π-conjugation of the TTTP endows low-lying HOMO energy levels, improved interfacial contact and defect passivation, as well as enhanced hole extraction/transport capacity for TTTP-based HTMs. As a result, the TTTP core shows good compatibility to either planar or twisted donor. Perovskite solar cells (PSCs) based on both WH01 and WH02 realize power conversion efficiencies (PCEs) of around 21%. The optimized PSCs adopting WH01 exhibit a champion PCE of 21.54%, which significantly outperforms the reference M130 (18.85%). Furthermore, the un-encapsulated devices with TTTP-series HTMs demonstrate excellent operational stability under ambient air. This systematic study highlights that TTTP-based molecules are promising potential candidates as HTMs for achieving highly efficient and stable PSCs.