Rational Design of SFT-Based Hole Transport Materials with Diversified Terminal Acceptors for Efficient Perovskite...

Efficient hole-transporting materials (HTMs) are crucial for improving the power conversion efficiency (PCE) and operational stability of perovskite solar cells (PSCs). Nevertheless, the rational design of organic HTMs that simultaneously combine suitable energy-level alignment, visible transparency, good chemical stability, facile film formation, and efficient hole-transport characteristics remains a major challenge. In this work, first-principles calculations were employed to investigate the structural, optical, electrochemical, solubility, chemical stability, and charge-transport properties of five spirofluorenedithiolane-based derivatives (SFT1-SFT5), designed through thiophene-bridged end-capped acceptor engineering of the parent SFT-STPA molecule. The designed HTMs exhibit suitable frontier orbital alignment with the perovskite absorber, indicating favorable hole extraction and transport. Their highest occupied molecular orbitals (HOMO) energies range from - 5.15 to -5.26 eV, indicating improved stabilization relative to the reference molecule (-5.07 eV). Moreover, the designed derivatives retain absorption maxima below 470 nm, which helps minimize parasitic absorption and preserve effective light harvesting by the perovskite layer. Reduced reorganization energies (0.3032-0.3933 eV), higher hole-transfer integrals (0.1250-0.1690 eV), and rapid hole-transfer rates collectively indicate favorable hole-transport behavior. In addition, more favorable solvation free energies (-56.84 to -47.92 kcal mol^- 1) suggest improved processability and film-forming ability. Overall, these results identify spirofluorenedithiolane-based derivatives as promising HTM candidates for high-performance PSCs.