Small Energetic Disorder Enables Ultralow Energy Losses in Non-Fullerene Organic Solar Cells

The relatively large non-radiative recombination energy loss (Delta E-3) is the main source of energy losses in organic solar cells (OSCs). The energetic disorder plays a crucial role in non-radiative energy losses; however, reducing the energetic disorder by modifying terminal groups has rarely been investigated. Herein, four acceptors, BTP-ICB1F, BTP-ICB2F, BTP-ICB3F, and BTP-ICBCF3, with fluorinated phenyl terminal groups are reported at identified substitution sites. The theoretical and experimental results show that this system possesses smaller energetic disorder than the generally-used Y6 acceptor due to the strong electron polarization effect arising from tight, 3D molecular packing. Therefore, the PM6:BTP-ICBCF3 combination achieves high efficiency of 17.8% with high open circuit voltage (V-OC) of 0.93 V and ultralow Delta E-3 of 0.18 eV, which is the smallest Delta E-3 for the binary OSCs with power conversion efficiency (PCEs) over 17% reported to date. Lastly, using the ternary strategy by incorporating the BTP-ICBCF3 acceptor into PM6:BTP-eC9, a higher PCE of 18.2% is achieved with enhanced V-OC. The results imply that introducing new terminal groups in acceptors is promising for reducing energetic disorder and energy losses.

Automated summary

Non-radiative recombination energy loss (△E-3) is the main source of energy losses in organic solar cells (OSCs). Reducing the energetic disorder by modifying terminal groups has rarely been studied. In this study, acceptors with fluorinated phenyl terminal groups were investigated. The results show that these acceptors have smaller energetic disorder and achieve high efficiency and ultralow △E-3.