A research group led by Prof. GE Ziyi at the Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences (CAS), has developed two isomeric non-fullerene acceptors and doped them into the D18:N3-based binary organic solar cells (OSCs) as a third component, resulting in highly efficient rigid and flexible ternary OSCs with the power conversion efficiency (PCE) of 19.3% and 18.0%, respectively. This work was published in Energy & Environmental Science.
Thanks to the advantages of flexibility, portability, and transparency, OSCs enjoy a promising prospect in the field of green energy technology. Currently, the ternary strategy is one of the efficient methods to improve the performance of OSCs. The strategy of isomerization has been considered as an effective way to improve the efficiency of OSCs by optimizing molecular structures. Previous studies on isomer effects have focused on binary OSCs, with only a few works concerning ternary OSCs.
To address this issue, the researchers at NIMTE synthesized two large π-conjugated isomers of Y6-derivatives, i.e., QX-α and QX-γ, with the same molecular formula but different orientations of their fused thiophene-rings.
The two isomers were introduced into the D18:N3-based binary devices as a third component, respectively. Thus the influence of isomers in non-fullerene guest acceptors on their photovoltaic properties were investigated in detail.
Compared with QX-γ, QX-α has a stronger dipole moment, a more ordered stacking, and a higher surface energy, owing to the S···N non-covalent interactions. The developed D18:N3:QX-α-based ternary OSCs reached an excellent PCE of 19.33%, while the D18:N3:QX-γ-based device only exhibited a PCE of 18.30%, which is comparable to the standard binary device with a PCE of 18.16%.
In addition, the flexible device based on the D18:N3:QX-α achieved an outstanding PCE of 18.01%, which is the highest value reported to date for flexible OSCs.
After being stored at 85 ℃ for 476 hours in an N2-filled glove box, the D18:N3:QX-α-based ternary device showed significant increases in efficiency retention from 49% to 87%, indicating an excellent thermal stability.
This ternary device retained over 97% of the initial PCE at room temperature for over 2,200 h. Moreover, the extrapolated T80 lifetime of the device reached 17,000 h, showing a broad prospect for commercial application.
The isomerization strategy has provided a promising effective route to develop non-fullerene guest acceptors for stable high-efficiency ternary OSCs.
This work was financially supported by the National Natural Science Foundation of China (No.U21A20331), National Science Fund for Distinguished Young Scholars (No.21925506), and Zhejiang Provincial Natural Science Foundation of China (No. LQ22E030013).
Fig. The molecular structures of N3, QX-α, and QX-γ (a); J-V curves of the rigid (b) and flexible (c) organic solar cells (Image by NIMTE)
Contact
YANG Daobin
Ningbo Institute of Materials Technology and Engineering
E-mail: yangdaobin@nimte.ac.cn