Self‐Assembled Molecular Interfaces for Suppressing Nonradiative Voltage Loss in Organic Photovoltaics

Suppressing nonradiative recombination voltage loss (Δ V nr ) is a critical challenge in developing highly efficient organic photovoltaics (OPVs). Although extensive efforts focus on materials design and active layer morphology optimization, the properties of interfacial layers also play a pivotal role in determining Δ V nr . This study examines the impact of self‐assembled molecules (SAMs) on Δ V nr reduction using a state‐of‐the‐art PM6:L8‐BO blend system as the active layer. Devices incorporating Br‐2PACz SAM as a hole‐transporting layer (HTL) are directly compared with conventional PEDOT:PSS‐based references. The Br‐2PACz‐based devices exhibit a pronounced improvement in open‐circuit voltage ( V OC ) relative to their PEDOT:PSS counterparts. Comprehensive morphological analyses reveal that the active layer nanostructure is independent of the underlying HTL, suggesting that the difference in V OC originates from interfacial rather than bulk effects. Voltage loss analysis further indicates that the V OC enhancement stems exclusively from the suppressed Δ V nr . This reduction in Δ V nr is attributed to a lower reverse saturation current density, suggesting that Br‐2PACz effectively mitigates surface recombination at the HTL/active layer interface. These findings highlight the critical role of interfacial engineering in minimizing Δ V nr and provide a viable pathway toward next‐generation high‐efficiency OPVs.