Abstract
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.
Highlights
The excitonic absorbers in organic solar cells (OSCs) rely on the donor−acceptor (D-A) interfaces to generate free charges
The energy of the interface charge transfer state (ECT) is considered as the effective bandgap of OSCs, while the difference between the absorber bandgap (ES1) and ECT is known as the energy loss, or driving force, required for charge generation
The best power conversion efficiency (PCE) of the fullerene-based OSCs currently stagnates at 11.48%
Summary
The excitonic absorbers in organic solar cells (OSCs) rely on the donor−acceptor (D-A) interfaces to generate free charges. Y6.14,15 As elaborated above, the value of ECT is a crucial parameter in the determination of driving force, recombination loss, and even the charge generation mechanism of these devices.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
