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 an alkoxy-substituted asymmetric conjugated molecule and successfully doped it into the PM6:BTP-eC9-based binary organic solar cells (OSCs) as a third component, resulting in high-efficiency ternary OSCs with the power conversion efficiency (PCE) of over 18.1%. This work was published in ACS Energy Letters.

Thanks to the various promising advantages, such as solution processability, transparency, portability, and flexibility, OSCs have attracted great attentions in the clean solar energy field. The ternary strategy is widely acknowledged as a facile and efficient method to improve the performance of OSCs.

However, the "structure-performance" correlations for the ternary device have rarely been illuminated thoroughly and systematically to date. Therefore, it is urgent to reveal the correlation among molecular structure, active layer morphology and photovoltaic performance, thus providing an effective strategy for achieving high-performance OSCs.

To address issue, researchers at NIMTE synthesized three asymmetric skeleton non-fullerene (ASNF) acceptors, i.e., TB-S, TB-S1, and TB-S1-O, and employed them as the third component in the host binary system of PM6:BTP-eC9, respectively.

Benefiting from the additional noncovalent conformation lock, the alkoxy-substituted TB-S1-O possessed a wide band gap, stable planar conformation, high surface energy, excellent compatibility with the host materials, and a large ordered stacking domain, which shows superior performances than TB-S, TB-S1.

Notably, the PM6:BTP-eC9:TB-S1-O ternary film possesses an ideal interpenetrating network, contributing to a reduction in nonradiative voltage loss and an enhancement in charge transport. Consequently, when researchers blended TB-S1-O into the PM6:BTP-eC9 system, a significant increase of PCE from 17.36% of binary film to 18.14% of ternary film was demonstrated.

Due to the inferior morphology, the devices based on PM6:BTP-eC9:TB-S and PM6:BTP-eC9:TB-S1 show a remarkably lower PCE (i.e., 16.16% and 16.18%, respectively), in comparison with the PM6:BTP-eC9:TB-S1-O based ternary device.

This work demonstrated that asymmetric skeleton with alkoxy-substitution is an efficient strategy to construct the third component for high-performance ternary OSCs.

The study was financially supported by the National Science Fund for Distinguished Young Scholars (No. 21925506), National Natural Science Foundation of China (Nos. U21A20331, 81903743, and 22171153), Zhejiang Provincial Natural Science Foundation of China (No. LQ22E030013), Ningbo key scientific and technological project (No. 2022Z117), Ningbo Natural Science Foundation (No. 2021J192), and Ningbo Science and Technology Bureau under CM2025 Programme (No. 2020Z092).

Fig. The chemical structures of TB-S, TB-S1, TB-S1-O, and J-V curves of their ternary organic solar cells. (Image by NIMTE)

Contact
YANG Daobin
Ningbo Institute of Materials Technology and Engineering
E-mail: yangdaobin@nimte.ac.cn