A Reactive Monte Carlo Model of Molecular Doping in Organic Semiconductors*

Organic semiconductors (OSCs) enable a new technological paradigm of solution-processable, lightweight, flexible, and low-cost optoelectronic devices. Analogous to silicon microelectronics, the addition of electronic dopants is a ubiquitous performance augmentation strategy in OSCs to improve conductivity. Although the importance of optimizing OSC/dopant interactions is well-recognized, challenges arise from experimental structure-function relationships being subject to the sensitivity of doping to processing conditions and film morphology. Computational modelling for OSC/dopant design may decouple these effects but requires simultaneous treatment of molecular electronic structure and mesoscale morphology. We present a reactive Monte Carlo model that samples the morphologies of molecularly doped OSCs to clarify the dependence of the doping efficiency on local electrostatics, integer charge transfer reaction free energy, and film morphology. Simulations highlight the dominant role of electrostatics-driven dopant aggregation and the minor role of single molecule energetics in modulating doping efficiency. Experimental ramifications and design criteria for molecular dopants in light of these results will be discussed.