Spatial Control of Spontaneous Orientation Polarization for Efficient Charge Separation in Organic Photovoltaics

Abstract

ABSTRACT Spontaneous orientation polarization (SOP) offers a unique approach to generating internal electric fields in organic photovoltaics (OPVs). However, in conventional high‐performance OPVs based on bulk heterojunction architectures, the complex nanoscale morphology makes it difficult to isolate the intrinsic role of SOP in charge dynamics. Herein, a planar heterojunction model is constructed using an acceptor pair with nearly identical electron affinities and molecular backbones but markedly different SOP magnitudes, enabling the selective evaluation of SOP‐induced electrostatic effects. An ultrathin SOP layer inserted directly at the donor/acceptor interface efficiently promotes exciton dissociation, significantly improving the fill factor and power conversion efficiency. Conversely, displacement current measurements quantitatively reveal the adverse effects of SOP: increasing the thickness of the SOP layer generates a massive potential change within the SOP layer, triggering low‐voltage hole accumulation at the interface. This accumulation promotes exciton–polaron quenching (EPQ)‐like deactivation, resulting in voltage‐dependent photocurrent loss and reduced device performance. By decoupling this dual nature of SOP, this study demonstrates that spatial arrangement of SOP, in which an ultrathin polar layer is localized near the charge‐separation interface while suppressing excessive interfacial charge accumulation, is a general design principle for utilizing local electric fields in high‐performance OPVs.