Volatile Additive Assists Binary Layer‐by‐Layer Solution Processing Organic Solar Cells to Achieve 19% Efficiency

Comprehensive Summary Layer‐by‐layer (LbL) solution processing is an efficient method to realize high performance organic solar cells (OSCs). One of the drawbacks of the LbL‐processed active layer is the large difference in the crystallinity of the donor and acceptor, which will lead to imbalance charge transfer and result in unfavorable charge recombination. Herein, we combined a novel volatile additive 3,5‐dichloro‐2,4,6‐ trifluorobenzotrifluoride (DTBF) with the LbL method to realize high‐efficiency OSCs. DTBF interacts with the non‐fullerene acceptor BTP‐4F by non‐covalent bonding, which enhances the crystallinity and compact stacking of BTP‐4F. DTBF doped OSC has balanced and efficient electron transport properties, longer carrier lifetime, higher exciton dissociation and charge collection efficiencies, lower energetic disorder than the control OSC without any additives. Benefiting from the optimization of charge dynamics and micro‐morphology by DTBF, the binary LbL‐processed OSC achieved synergistic improvements in open‐circuit voltage, short‐circuit current density and fill factor. As a result, a champion power conversion efficiency ( PCE ) of 19% is realized for DTBF‐optimized OSC, which is superior to the control OSC (17.55%). This work demonstrates a promising approach to modulate active layer morphology and fabricate high performance OSCs.