Photon-induced isomerization enables high-performance polymer solar cells

Abstract

The introduction of isomeric components into the active layers demonstrates effective mitigation of morphological defects arising from thermodynamic immiscibility in all-polymer solar cells (all-PSCs). Nevertheless, conventional isomerization methods for donor and acceptor materials remain complex and challenging to implement for intensifying photovoltaic performance. To overcome this limitation, we propose a photo-isomerization strategy involving ultraviolet laser irradiation of polymer materials in solutions. Structural and photophysical characterizations reveal that neat polymer films present enhanced crystallinity, prolonged exciton lifetime, and extended exciton diffusion length through the isomeric component incorporation. These benefits further synergistically strengthens intermolecular π-π stacking interaction and optimizes vertical distribution gradient in the active layers fabricated via layer-by-layer deposition, delivering an ideal bicontinuous interpenetrating network morphology. Notably, the refined morphology of the active layers increases the proportion of local excitons converting into charge transfer states to facilitate exciton dissociation, improves charge transport, and suppresses charge recombination. Ultimately, the laser-processed PM6:PY-IT devices achieve a promising power conversion efficiency of 18.21% and ameliorated stability including both thermal stability and photostability. This work confirms that ultraviolet laser irradiation can serve as a facile and effective approach for inducing isomerization of organic photovoltaic materials, offering a photochemical perspective toward efficient and stable PSCs.