The origin of Urbach energy (E U ) in organic semiconductors and its effect on photovoltaic properties remain a topic of intense interest. In this letter, we demonstrate quantitative information on the E U value in emerging Y-series molecules by an in-depth analysis of the line shape of the temperature-dependent quantum efficiency spectra. We found that the static disorder (E U (0)), which is dominated by the conformational uniformity in Y-series acceptors, contributes 10−25 meV to the total Urbach energy. Particularly, this static contribution in organic solar cells (OSCs) is much higher than those (E U (0) ≈ 3−6 meV) in inorganic/hybrid counterparts, such as CH 3 NH 3 PbI 3 perovskite, crystalline silicon (c-Si), gallium nitride (GaN), indium phosphide (InP), and gallium arsenide (GaAs). More importantly, we establish clear correlations between the static disorder and photovoltaic performance and open-circuit voltage loss. These results suggest that suppressing the static disorder via rational molecular design is clearly a path for achieving higher performance.

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 (E CT) 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 E CT 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.

Photodetectors (PDs) based on organic materials exhibit potential advantages such as low-temperature processing, superior mechanical properties, and form factors. They have seen rapid strides towards achieving performance metrics comparable to...