Fused Dithienoheterocycle-Based Hole-Transporting Materials for Efficient Perovskite Solar Cells

The development of efficient and stable hole-transporting materials (HTMs) is critical for advancing perovskite solar cell (PSC) technology. This study presents two novel HTMs, LK-1 and LK-2, based on fused dithienoheterocycle derivatives, namely, dithieno[3,2-f:2′,3′-h]quinoxaline (DTQu) and dithieno[3,2-a:2′,3′-c]phenazine (DTPh), designed for PSCs. These donor–acceptor–donor (D–A–D) structured HTMs exhibit planar, rigid cores that enhance π–π stacking, improving hole mobility and stability. LK-1 and LK-2 were synthesized and characterized for their optical, electrochemical, and thermal properties. PSCs with LK-1 achieved a power conversion efficiency (PCE) of 18.16%, whereas LK-2 reached 19.40%, outperforming LK-1 due to smoother film properties and reduced recombination. Both HTMs showed high thermal stability and suitable energy alignment with the perovskite layer. LK-2-based PSCs enhanced hydrophobicity and film morphology further suggest its potential for stable, efficient PSCs, advancing the development of robust organic HTMs.