Dopant Complexes—A Highly Stable and Almost Universal Doping System for Organic Semiconductors

Chemical doping of organic semiconductors (OSCs) is mandatory in order to improve charge transport to the level required for applications such as thermoelectrics. However, the typical dopants used, such as F₄TCNQ or FeCl₃, invariably present limitations in terms of processability, thermal stability and/or generality. In this contribution, we will present Lewis-paired complexes as an alternative class of high-performance dopants that, remarkably, address all of the aforementioned drawbacks. Focus is given to solution-processable complexes formed by the Lewis acid BCF and F₄TCNQ bearing Lewis-basic -CN groups. Due to its exceptionally high electron affinity of ~6 eV, BCF:F₄TCNQ is shown to dope a broad range of OSCs (over 20 of which were studied) including non-fullerene acceptors and polyfluorenes. State of the art mobilities (up to 900 S cm^–1) can be obtained with this dopant system, which, moreover, exhibits a 3-fold higher dedoping activation energy compared to the neat constituent dopants making this a promising dopant system for thermoelectrics. Then, we will discuss the mechanism of complexation subsequent doping by looking at several Lewis acids, molecular dopants, and microstructures, as well as looking at DFT calculations. Finally, the capability of this system to be used for local doping will be demonstrated.