Nanomaterials - 12

Abstract

Chemical doping of organic semiconductors (OSCs) is a key technology for controlling their electronic properties, including their carrier injection properties. Chemical doping based on redox reactions has been performed under inert atmospheres to avoid undesired redox reactions with oxygen and water. In contrast, we successfully developed versatile p-type doping in air using aqueous solutions, in which the use of acidic solutions seemed to suppress the redox reaction with water [1]. However, it has been still difficult to achieve n-type doping in air, because conventional reducing agents can be deactivated by oxygen. This is problematic for the facile and large-scale fabrication of advanced OSC-based devices.
 In this study, an ambient n-type doping method was developed. A thin film of the polymer semiconductor PNDIT was reduced using fructose and flavin mononucleotide (FMN), which are environmentally friendly materials of biological origin. The reduction of PNDIT through immersion in the aqueous solution with these materials was confirmed by changes in the conductivity and UV-vis spectra, the mechanism of which is shown in the figure below. First, FMN accepts the electrons from fructose. The reduced FMN serves as a redox mediator, where PNDIT accepts electrons from the reduced FMN. The electrons in PNDIT are compensated by inert molecular cations, which improve the stability of the doped state. Diodes fabricated using this novel n-doping method will be also discussed.