In Situ Generation of n-Type Dopants by Thermal Decarboxylation

Molecular doping is a powerful and increasingly popular approach toward enhancing electronic properties of organic semiconductors (OSCs) past their intrinsic limits. The development of n-type dopants has been hampered, however, by their poor stability and high air-reactivity, a consequence of their generally electron rich nature. Here, the use of air-stable carboxylated dopant precursors is reported to overcome this challenge. Active dopants are readily generated in solution by thermal decarboxylation and applied in n-type organic field-effect transistors (OFETs). Both 1,3-dimethylimidazolium-2-carboxylate (CO2-DMI) and novel dopant 1,3-dimethylbenzimidazolium-2-carboxylate (CO2-DMBI) are applied to n-type OFETs employing well-known organic semiconductors (OSCs) P(NDI2OD-T2), PCBM, and O-IDTBR. Successful improvement of performance in all devices demonstrates the versatility of the dopants across a variety of OSCs. Experimental and computational studies indicate that electron transfer from the dopant to the host OSC is preceded by decarboxylation of the precursor, followed by dimerization to form the active dopant species. Transistor studies highlight CO2-DMBI as the most effective dopant, improving electron mobility by up to one order of magnitude, while CO2-DMI holds the advantage of commercial availability.