Hydroxylated secondary dopants for surface resistance enhancement in transparent poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) thin films

The addition of small, hydroxylated secondary dopants (SDs) can greatly decrease the surface resistance (SR) of poly(3,4-ethylenedioxy-thiophene)-poly(styrenesulfonate) (PEDOT-PSS) thin films with virtually no loss in film transparency. For example when 2,2'-thiodiethanol or glycerol are added to an aqueous suspension of PEDOT-PSS, thin films cast from the suspension exhibit approximately five-to-seven-fold decrease in surface electrical resistance while their optical transparencies remain nearly constant, or, in some cases, increase slightly. This behavior is strikingly different from that of conducting polymer films doped with standard ionic dopants, wherein decreases in surface resistance are accompanied by a sharp loss in film transparency. These findings may be important to the development of plastic "throwaway" electronics such as liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, imaging materials for flexible substrates, and organic field-effect transistors (FETs). Studies using mid-IR spectroscopic data and deuterated solvents support the premise that 2,2'-thiodiethanol enhances film properties by stabilizing the PEDOT-PSS electrostatic interactions. This dopant enables formation of films with conductivities as high as 98 S/cm and optical transparencies of 84%. Solution thermodynamic analysis indicates that it exerts a chaotropic effect on the aqueous solvent that may aid its ability to enhance film properties. (C) 2003 Elsevier B.V. All rights reserved.