Breaking the Voltage‐Loss Bottleneck in Organic Photovoltaics via Interfacial Molecular Orientation Engineering

ABSTRACT Benefiting from non‐fullerene acceptors, organic photovoltaics (OPVs) have achieved power conversion efficiencies exceeding 21%. However, further progress critically depends on suppressing voltage losses ( V loss ), particularly non‐radiative voltage losses (Δ V 3 ). Here, we employ a precisely controlled donor/acceptor bilayer system, fabricated via a polydimethylsiloxane (PDMS) film‐transfer method, to systematically investigate the intrinsic role of interfacial molecular orientation in governing V loss . Devices with a face‐on/face‐on (P5TCN‐F0/Y6) configuration exhibit markedly reduced Δ V 3 and overall V loss compared with edge‐on/face‐on (P5TCN‐F50/Y6), face‐on/edge‐on (P5TCN‐F0/BTP‐2T), and edge‐on/edge‐on (P5TCN‐F50/BTP‐2T) counterparts. Transient absorption spectroscopy and time‐resolved photoluminescence measurements reveal that the face‐on/face‐on interface enables efficient charge transfer while suppressing charge‐transfer (CT) states recombination. Quantitative analysis further demonstrates that the markedly reduced non‐radiative recombination rate of the CT states is responsible for the enhanced electroluminescence quantum efficiency and the reduced Δ V 3 and V loss . These findings establish interfacial molecular orientation as a key lever for minimizing Δ V 3 without compromising high photocurrent and provide material design principles and morphology control requirements for further breaking the performance bottleneck in bulk heterojunction OPVs.