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

Abstract

AbstractThe relatively large non‐radiative recombination energy loss (ΔE3) 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 (VOC) of 0.93 V and ultralow ΔE3 of 0.18 eV, which is the smallest ΔE3 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 VOC. The results imply that introducing new terminal groups in acceptors is promising for reducing energetic disorder and energy losses.