Regulating Film-Formation Kinetics via Tetraphenylethylene Functionalization for Efficient Organic Solar Cells

Abstract

Controlling film-formation kinetics remains a central challenge for optimizing morphology evolution and charge-generation processes in organic solar cells (OSCs). Herein, we develop a facile molecular engineering strategy to regulate film-formation kinetics through tetraphenylethylene (TPE) functionalization and design a new non-fullerene acceptor, BTP2F-TPE. The incorporation of bulky TPE units introduces pronounced steric hindrance, effectively suppressing excessive molecular aggregation and modulating intermolecular interactions during film formation. As a result, the D18:BTP2F-TPE blend exhibits a substantially higher solution-to-film transition rate (5.00 s^-1) than the D18:L8-BO counterpart (3.33 s^-1), leading to a more favorable phase-separated morphology. When incorporated as a third component into D18:L8-BO, BTP2F-TPE enables the ternary blend to achieve enhanced exciton dissociation, more efficient charge collection, and reduced non-radiative energy loss (0.210 eV). Consequently, the ternary device delivers a power conversion efficiency of 20.28%, with an open-circuit voltage of 0.907 V, a short-circuit current density of 27.72 mA·cm⁻², and a fill factor of 80.62%. Femtosecond transient absorption spectroscopy reveals accelerated hole transfer at the donor–acceptor interface, supporting the improved charge-generation dynamics observed in the ternary system. This work demonstrates that manipulating film-formation kinetics through steric side-chain engineering represents an effective strategy for optimizing active-layer morphology and advancing high-performance organic photovoltaics.