Unveiling the Microscopic Origin of Non-Radiative Voltage Loss in Organic Solar Cells through a Controlled...

Non-radiative voltage loss (ΔV_nr) is a major factor limiting the efficiency of organic solar cells (OSCs), yet its microscopic origin remains unclear due to the complex morphology of bulk heterojunction photoactive layers. In this work, we design a triple-layer device configuration that controls the density of donor/acceptor (D/A) interfaces without changing the composition or thickness of the photoactive layer. This strategy decouples interfacial characteristics, material parameters, and device performance, allowing us to direct probe their intrinsic relationships. We find that ΔV_nr originates not only from carrier lifetime effects but also from thermodynamic redistribution between locally excited (LE) and charge-transfer (CT) states. Increasing the density of D/A interfaces broadens the excitonic density of states, reduces the activation energy for LE-to-CT conversion, and enhances recombination via non-radiative CT channels. Strong correlations among Urbach energy (E_U), activation energy, and ΔV_nr highlight their critical role in governing voltage losses in OSCs. Our results clarify the microscopic mechanisms behind non-radiative losses and offer a general design strategy to suppress ΔV_nr in next-generation OSCs.