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

Comprehensive Summary 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.