Light-induced quinone conformation of polymer donors toward 19.9% efficiency organic solar cells

Modulating the self-assembly process of polymer donors is crucial to acquire an ideal morphology of the photoactive layer for efficient photovoltaics, however, this always requires complicated chemical synthesis or comprehensive physical treatments. In this work, a facile morphology optimization method was realized by irradiating polymer solutions with a 365 nm UV-light for achieving enhanced intermolecular ordering of polymer donors. Fourier transform infrared spectroscopy and Raman spectroscopy reveal that light irradiation can disrupt the aromatic conformation of polymers and induce the formation of a rigid quinone structure. Synchrotron X-ray diffraction suggests that the rigid qunione skeleton improves the planarity of polymers to form compact aggregates with enhanced π-π stacking in their pristine and blend thin films with non-fullerene acceptor L8-BO. As a result, both PM6:L8-BO and D18:L8-BO based devices exhibited enhanced carrier transport and suppressed recombination, leading to power conversion efficiency (PCE) enhancements from 18.8% to 19.7% and from 18.9% to 19.6%. The versatility of this strategy is also verified using more polymer donors including PTB7-Th and PBDB-T. Impressively, the D18:PM6:L8-BO ternary system delivered a maximum PCE of 19.9%, which is among the highest value of single-junction organic solar cells. UV-light illumination converts the aromatic conformation of polymer donors into a rigid quinone structure, resulting in compact fibrillar aggregation of the active layer to achieve a maximum efficiency of 19.9% of single-junction organic solar cells.