Judicious Molecular Design of 5H‑Dithieno[3,2‑b:2',3'‑d]Pyran-based Hole-Transporting Materials for Highly Efficient and Stable Perovskite Solar Cells

The structural modification of hole-transporting materials (HTMs) is an effective strategy for enhancing photovoltaic performance in perovskite solar cells (PSCs). Herein, a series of dithienopyran (DTP)-based HTMs (Me-H, Ph-H, CF3-H, CF3-mF, and CF3-oF) is designed and synthesized by substituting different functional groups on the DTP unit and are used fabricating PSCs. In comparison with Me-H having two methyl substituents on the dithienopyrano ring, the Ph-H having two phenyl substituents on the ring exhibits higher PCEs. Notably, the incorporation of trifluoromethyl groups in CF3-H endows the molecule with a larger dipole moment, deeper HOMO energy level, better film morphology, closer molecular stacking, more efficient defect-passivation, enhanced hydrophobicity, and better photovoltaic performance when compared with the Ph-H counterpart. Furthermore, the HTMs of CF3-mF and CF3-oF, which feature fluorine-substituted triphenylamine, demonstrated excellent film-forming properties, more suitable energy levels, enhanced charge mobility, and improved passivation of the buried interface between HTMs and perovskite. As a result, PSCs employing CF3-mF and CF3-oF gave impressive PCEs of 23.41 and 24.13%, respectively. In addition, the large-area (1.00 cm²) PSCs based on CF3-oF achieved a PCE of 22.31%. Moreover, the PSCs devices with CF3 series HTMs exhibited excellent long-term stability under different conditions.