Biochemical Pathways for n-Type Doping: An Electron Transfer Relay from Saccharide to Organic Semiconductors

Solution processing of organic semiconductors provides a facile way to fabricate electrically doped thin films, which opens opportunities for advancing printed electronics. However, this approach is limited due to the instability of dopants and doped organic semiconductors, particularly for n-type ones. In this study, n-type doping of an organic semiconducting polymer is achieved using aqueous doping solutions in air, a condition under which n-type chemical doping had not previously been demonstrated. Polymeric semiconductor thin films are immersed in aqueous doping solutions, which contained the saccharide fructose, redox bio-mediator flavin nucleotide (FMN), and bulky molecular cations. In this process, electrons are transferred from fructose to FMN and then from FMN to organic semiconductor thin films. The introduced electrons are compensated by the incorporation of bulky molecular cations into the thin films. Successful n-type doping is confirmed by absorption, conductivity, and photoelectron spectroscopy measurements. The density of states of the polymer is filled up to -3.8 eV versus vacuum, beyond the conventionally anticipated limit of ambient stability. This breakthrough is rooted in the combined effects of solution pH, mediator-assisted use of fructose, and choice of dopant cation. In addition, n-type doping using biomolecules may shed light on new connections between electronic materials and biomolecules for energy storage, transfer, and conversion.