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

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 (ΔV₃). 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 ΔV₃ 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 ΔV₃ and V_loss. These findings establish interfacial molecular orientation as a key lever for minimizing ΔV₃ without compromising high photocurrent and provide material design principles and morphology control requirements for further breaking the performance bottleneck in bulk heterojunction OPVs.