Researchers have developed a doping method for organic semiconductors that increases hole densities by up to two orders of magnitude using molecular dopants designed to chemically degrade after charge transfer, according to a study published in Nature Materials.
The mechanism, termed degradation-assisted doping, bypasses the thermodynamic equilibrium that typically halts doping when chemically stable dopants are used. In standard chemical doping, electron transfer ceases once an equilibrium is established between the semiconductor host and the dopant. Under the degradation approach, p-dopants break down via their radical anion after electron transfer takes place. This chemical degradation removes reaction products from co-defining the equilibrium, allowing the doping reaction to persist despite a dopant with limited initial electron affinity.
A research team led by Ingo Salzmann of Concordia University alongside collaborators from the Institut national de la recherche scientifique and York University demonstrated the mechanism using the Lewis acid tris(pentafluorophenyl)borane, known as BCF. When combined with poly(3-hexylthiophene), BCF radical anions degrade in chloroform to yield chlorinated products, primarily [Cl-B(C6F5)3]− and [Cl2-B(C6F5)2]−. Density functional theory calculations identified these degradation steps as exothermic, releasing −0.72 eV and −0.84 eV.
Kinetic measurements using electron paramagnetic resonance spectroscopy showed that the reaction proceeds substantially faster in chloroform than in toluene. The researchers evaluated several alternative Lewis acid dopants, including perfluoropentaphenylborole, perfluoroboratriptycene, and tris(perfluorobiphenyl)borane, to establish a theoretical framework for future molecular design.
