Affiliation:
1. State Key Laboratory of Silicon and Advanced Semiconductor Materials Department of Polymer Science and Engineering Zhejiang University Hangzhou 310027 P. R. China
2. Zhejiang University‐Hangzhou Global Scientific and Technological Innovation Center Hangzhou 311200 P. R. China
3. School of Physics State Key Laboratory of Crystal Materials Shandong University Jinan Shandong 250100 P. R. China
4. School of Chemistry Beijing Advanced Innovation Center for Biomedical Engineering Beihang University Beijing 100191 P. R. China
Abstract
AbstractIn organic solar cells (OSCs), electron acceptors have undergone multiple updates, from the initial fullerene derivatives, to the later acceptor‐donor‐acceptor type non‐fullerene acceptors (NFAs), and now to Y‐series NFAs, based on which efficiencies have reached over 19%. However, the key property responsible for further improved efficiency from molecular structure design is remained unclear. Herein, the material properties are comprehensively scanned by selecting PC71BM, IT‐4F, and L8‐BO as the representatives for different development stages of acceptors. For comparison, asymmetric acceptor of BTP‐H5 with desired loosely bounded excitons is designed and synthesized. It's identified that the reduction of intrinsically exciton binding energy (Eb) and the enhancement of exciton delocalization capability act as the key roles in boosting the performance. Notably, 100 meV reduction in Eb has been observed from PC71BM to BTP‐H5, correspondingly, electron‐hole pair distance of BTP‐H5 is almost two times over PC71BM. As a result, efficiency is improved from 40% of S‐Q limit for PC71BM‐based OSC to 60% for BTP‐H5‐based one, which achieves an efficiency of 19.07%, among the highest values for binary OSCs. This work reveals the confirmed function of exciton delocalization capability quantitatively in pushing the efficiency of OSCs, thus providing an enlightenment for future molecular design.
Funder
National Natural Science Foundation of China
Fundamental Research Funds for the Central Universities