Probing into the Intrinsic Ambipolarity and Anisotropy of Carrier Transport Mechanisms in Nonfullerene Acceptor COi8DFIC Single Crystals

Carrier transport is a critical aspect of organic optoelectronics. This study presents a comprehensive investigation of the ambipolar and anisotropic carrier transport properties and mechanisms in single crystals of the nonfullerene acceptor COi8DFIC. To achieve this, a lateral time-of-flight (TOF) technique was employed. COi8DFIC films with long-range ordered molecular packing were prepared, and the growth direction of the crystals was confirmed to be perpendicular to the crystal (11̅1̅) face. The in-plane carrier transport properties were then characterized in orientations parallel and perpendicular to the growth direction, revealing ambipolar transport in both orientations. By examining the correlation between drift mobility and temperature or electric field, we observed a Gaussian disorder model for hole transport, showcasing varying levels of energetic and positional disorder along the two orientations. Furthermore, we observed a variable range hopping model for electron transport with different hopping distances along the two orientations.