Asymmetric Alkoxy and Alkyl Substitution on Nonfullerene Acceptors Enabling High‐Performance Organic Solar Cells

Abstract

In this paper, a strategy of asymmetric alkyl and alkoxy substitution is applied to state‐of‐the‐art Y‐series nonfullerene acceptors (NFAs), and it achieves great performance in organic solar cell (OSC) devices. Since alkoxy groups can have a significant influence on the material properties of NFAs, alkoxy substitution is applied to the Y6 molecule in a symmetric manner. The resulting molecule (named Y6‐2O), despite showing improved open‐circuit voltage (Voc), yields extremely poor performance due to low solubility and excessive aggregation properties, a change that is due to the conformational locking effect of alkoxy groups. In contrast, asymmetric alkyl and alkoxy substitution on Y6, yields a molecule named Y6‐1O that can maintain the positive effect of Voc improvement and obtain reasonably good solubility. The resulting molecule Y6‐1O enables highly efficient nonfullerene OSCs with 17.6% efficiency and the asymmetric side‐chain strategy has the potential to be applied to other NFA‐material systems to further improve their performance.

Ternary Organic Photovoltaic Cells Exhibiting 17.59% Efficiency with Two Compatible Y6 Derivations as Acceptor

“…The Y6‐1O‐based binary OPVs show a relatively large V OC of 0.904 V in comparison with that of 0.845 V for the BTP‐BO‐4F‐based binary OPVs, which can be well explained from the LUMO energy levels (−3.84 eV vs −4.06 eV) of Y6‐1O and BTP‐BO‐4F. [ 28 ] The V OC values of ternary OPVs were gradually enhanced along with the Y6‐1O content increment, indicating the sequentially evaluated LUMO levels of the alloyed acceptor BTP‐BO‐4F:Y6‐1O. Meanwhile, the J SC values of ternary OPVs are increased along with the Y6‐1O content up to 15 wt% and then decreased by incorporating more Y6‐1O.…”

Pseudo-bilayer architecture enables high-performance organic solar cells with enhanced exciton diffusion length

“…Donor polymer PM6 ( M n : 24.2 kDa; M w : 88.0 kDa; PDI: 3.361) was provided by Solarmer Materials Inc. PC 71 BM was purchased from Sigma-Aldrich. N3 and Y6-O were synthesized according to the procedures in the literatures 27 , 58 .…”

Side‐Chain Engineering on Y‐Series Acceptors with Chlorinated End Groups Enables High‐Performance Organic Solar Cells

“…[46] Last but not least, the outer side chains can introduce steric hindrance between the rigid fused cores and the end groups, resulting in the so-called "conformational locking effect" to reduce the number of stereoisomers and change the planarity of the molecules, which will in turn affect the molecular packing and change the morphological properties of the active layers. [47][48][49] Previously, our group have devoted a lot of efforts in outer sidechain engineering, [19,46,50,51] among which the asymmetric alkyl-alkoxy substitution strategy has shown great potential for the Y-series acceptors since this modification can maintain the advantages of alkoxy substitution to achieve a higher V OC while preventing over-aggregation caused by the alkoxy groups. As a result, the asymmetric acceptor named Y6-1O (Figure 1)-based ternary devices can achieve an excellent PCE of 17.6%.…”