MR-TADF emitter as a dual-functional solid additive to extend exciton lifetime and optimize morphology for organic solar cells with ∼19% efficiency

Extending exciton lifetime and optimizing active-layer morphology simultaneously to advance power conversion efficiency (PCE) of organic solar cells (OSCs) still encounter great challenges by conventional additive strategies. Herein, to address these issues, a multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitter of BNS-H1 containing heteroatom-embedded polycyclic aromatic hydrocarbon is innovatively served as a dual-functional solid additive (DFSA) in OSCs. The primary studies on the PM6:Y6 system indicate that BNS-H1 plays an exceptional dual-functional role in promoting π-π stacking of Y6 component and optimizing active-layer morphology. Meanwhile, the steady/transient photoluminescence spectra and transient photocurrent measurements further reveal that incorporating BNS-H1 with the system enhances emission of PM6 component, extend exciton lifetime and diffusion distance. Consequently, four types of binary OSCs demonstrate a notable improvement in PCE processed by 1.0 wt% BNS-H1. Specifically, the BNS-H1-treated OSCs with PM6:Y6 and PM6:BTP-eC9 systems achieve outstandingly increasing PCEs of 17.4% and 18.8% compared to their BNS-H1-free control devices, respectively. Furthermore, device stability of the BNS-H1-treated PM6:Y6 devices is significantly enhanced. Notably, the approaching 19% efficiency is one of the highest PCEs in the reported non-volatile additives treated binary OSCs. Our work highlights the significant potential of MR-TADF emitter as a DFSA in OSCs for boosting PCEs.