Nonhalogenated Solution-Processed Donor-Dispersed Planar Heterojunction Organic Solar Cells with Enhanced Homogeneity in Vertical Phase Separation

Realization of state-of-the art efficiencies in organic photovoltaics (OPV) generally relies on using toxic halogenated solution processing to arrive at the desired nanomorphology and optoelectronic responses, whereas the photovoltaic performance in nonhalogenated solution (NHS)-based OPVs is yet nonsatisfactory, mainly related to the difficulty of morphological control. Herein, a conceptual approach of donor-dispersed planar heterojunction (DD-PHJ) for improving the regulation of phase morphology and photovoltaic behaviors in NHS-processed OPVs is proposed, afforded by dispersing an ordered liquid crystal guest donor BTR-Cl into the nonfullerene acceptor host with sequential film deposition. The combined investigation shows that the inclusion of BTR-Cl plays a regulatory role in enhancing the crystallization, intermolecular donor/acceptor miscibility, and homogeneity in the donor–acceptor phase separation along vertical direction, which is conducive to improved charge transfer and reduced photovoltage loss. Of importance, the described DD-PHJ approach is applicable to representative OPV material systems, leading to a champion efficiency of 18.21% in devices prepared with NHS. This work provides a promising prospect toward high-efficiency and green solution-processed OPV devices.