Simultaneous Modulation of Interfacial Dipole and Film Kinetics via Self-Assembled Monolayers for Low-Energy-Loss Organic Photovoltaics
Self-assembled monolayers (SAMs) enable precise tuning of the ITO/active layer interfacial dipole, yet their impact on the crystallization kinetics of the overlying active layer remains poorly understood, limiting their potential in high-efficiency organic solar cells. This study introduces THPC, a self-assembling material with an extended carbazole core and heteroatom substitution, as a hole transport layer (HTL). Unlike the hydrophilic PEDOT:PSS, THPC exhibits low surface energy, providing a favorable template that extends the film formation kinetics of the PM6:L8-BO-X blend by nearly 1.4 times, mitigating the explosive nucleation prevalent in PM6-based active layers. This promotes a highly ordered fibrous morphology and enhances vertical phase separation. The deep work function of THPC (5.32 eV) increases the built-in potential, reduces interfacial trap density, and facilitates charge extraction. Consequently, non-radiative recombination loss decreases from 0.243 eV to 0.227 eV, and the open-circuit voltage rises from 0.866 V to 0.883 V, yielding a power conversion efficiency (PCE) of 20.19%, outperforming the PEDOT:PSS control (18.67%). This finding is confirmed across multiple Y-series acceptors, all approaching 20% PCE. Notably, the D18:L8-BO system achieves a PCE of 20.55%, demonstrating broad applicability.