Direct Observation of the Charge Transfer States from a NonFullerene Organic Solar Cell with a Small Driving Force
Peng Wan1, Xingtong Chen1, Qi Liu2, Sudhi Mahadevan3, Mingxuan Guo1, Jinjing Qiu2, Xiaojuan Sun1, Sai-Wing Tsang3,*, Maojie Zhang2,*（张茂杰）, Yongfang Li2, and Song Chen1,*（陈崧）
1 College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, PR China
2 State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, Laboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, PR China
3 Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR 999077, China
J. Phys. Chem. Lett. 2021, 12, 10595--10602
For organic solar cells (OSCs), the charge generation mechanism and the recombination loss are heavily linked with charge transfer states (CTS). Measuring the energy of CTS (ECT) by the most widely used technique, however, has become challenging for the non-fullerene-based OSCs with a small driving force, resulting in difficulty in the understanding of OSC physics. Herein, we present a study of the PM6:Y6 bulk heterojunction. It is demonstrated that electro-absorption can not only reveal the dipolar nature of Y6 but also resolve the morphology-dependent absorption signal of CTS in the sub-bandgap region. The device with the optimum blending weight ratio shows an ECT of 1.27 eV, which is confirmed by independent measurements. Because of the charge transfer characteristics of Y6, the charge generation at PM6:Y6 interfaces occurs efficiently under a small but non-negligible driving force of 0.14 eV, and the total recombination loss is as low as 0.43 eV.
链接：//pubs.acs.org/doi/10.1021/acs.jpclett.1c03365
