Nanomaterials - 11

Abstract

Chemical doping methods based on redox reactions for molecular semiconductors have been developed to enhance the properties of optoelectronic devices. However, maximizing the device performance requires precise control of the doping levels at the thermal energy scale (25 meV), which is challenging due to the difficulty in finely tuning the redox potential of the dopants. In addition, conventional dopants are prone to react with water or oxygen in air, which reduces controllability and reproducibility even in an inert atmosphere. These challenges present a significant bottleneck for the industrial fabrication of advanced OSC-based devices.
 In this study, the doping levels of molecular semiconductors were precisely and reproducibly controlled in aqueous solutions under ambient conditions[1]. As shown in the figure below, a spin-coated thin film of the polymer semiconductor PBTTT was doped through a proton-coupled electron transfer (PCET) reaction of benzoquinone (BQ) and hydroquinone (HQ). PCET is integral to biological processes such as metabolism, where the redox potential can be precisely tuned by proton activity (pH). Our experimental results demonstrated that the Fermi level of the PBTTT was controlled with a high degree of precision, ca. thermal energy of 25 meV at RT and over a few hundred meV around the band edge. This versatile doping method facilitates facile, scalable, precisely controlled, and reproducible device fabrication through ambient processing.