Synthesis of a Stable Radical Cation of Bis-Tert-Butyl Ethylenedioxythiophene and its Application as a Dopant in Organic Semiconductors

Abstract

A highly stable molecular radical cation (RC) derived from ethylenedioxy thiophene (EDOT) is effectively utilized for the p-doping of poly-3-hexylthiophene (P3HT), an organic semiconductor. The success of this process is due to efficient electron transfer from the highest occupied molecular orbital band of P3HT to the singly unoccupied molecular orbital of the radical cation species. Confirmation of the doping is experimentally confirmed through UV-vis-NIR absorption spectroscopy and electron spin resonance spectroscopy. The ability to dope the conjugated polymers PBTTT and PTB7 is also spectroscopically confirmed. An increase in work-function of P3HT upon doping is observed due to electron transfer from P3HT to the radical cation with a concomitant decrease in the Fermi energy of P3HT. Impedance and four point probe analysis showed that the doped polymer films exhibited a significant decrease in resistance compared to the pristine films. This work presents the first use of a stable, easily synthesized EDOT-based radical cation as a molecular p-dopant for conjugated polymers, offering a novel and broadly applicable alternative to traditional dopants such as F4TCNQ.