Small molecular glycosylated nitroxide radical additives enable efficient suppression of the non-radiative energy loss of non-fullerene acceptors-based organic solar cells

초록

Nitroxide radical-conjugated polymer additives (nr-PAs) have been employed as newly emerged additives to mitigate the non-radiative energy loss (Elossnon_ rad), thus to boost the performance and stability of the non-fullerene acceptors-based organic solar cells (NFAs-OSCs). Herein, the small molecular nitroxide radical compounds (SMTEMPO) of racemic 4-glycidyloxy-substituted 2,2,6,6-tetramethylpiperidine-1-oxyl (GTEMPO), the stereoisomers of (R)-GTEMPO and (S)-GTEMPO, are employed as the additives for NFAs-OSCs. Upon addition of 1.0 wt% (relative to the weight of polymer donor) of the SM-TEMPO radical additives, the power conversion efficiencies (PCEs) of the devices improved as follows: PM6:Y6: from 15.73% (pristine) to 16.46% (GTEMPO), 17.20% ((R)GTEMPO), and 16.91% ((S)-GTEMPO). D18-Cl:L8-BO: from 17.53% (pristine) to 18.66% (GTEMPO), 19.42% ((R)-GTEMPO), and 19.38% ((S)-GTEMPO). On the contrary, the addition of the unglycidylated 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical additive always results in a slight decrease in the PCEs of the PM6:Y6based NFAs-OSCs. Moreover, the reasons behind the performance enhancement, as well as the specific correlation between the improved performances of NFAs-OSCs and the difference in aggregation behaviours between the SM-TEMPO and TEMPO radical additives, are investigated and discussed through a set of physical investigations of representative PM6:Y6-based blends and devices. This work not only demonstrates that SMTEMPO radical additives, which tend to aggregate in the active layer, can serve as effective additives to improve the performance and stability of the NFAs-OSCs as their nr-PAs counterparts, but also points towards simpler avenues for the development of the nitroxide radical-based additives to achieve high-performance NFAsOSCs with enhanced stability.

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