Enhancement of polymer electronics via surface states on highly doped polymeric anodes

Organic optoelectronic devices that can be operated as organic light-emitting diodes and solar cells have been prepared using a poly(phenylenevinylene) (PPV)-based polymer as the active layer. Poly(3,4-ethylenedioxythiophene) (PEDOT) was grown potentiostatically atop indium-fin oxide to serve as the hole-injecting/collecting electrode, and its work function (phi(W)) was pre-adjusted by electrochemically altering the doping level. Subsequent controlled exposure to atmosphere produced devices with approximately constant open-circuit voltages consistent with the creation of an air-induced interfacial layer atop the PEDOT, which determines its Fermi level. The short-circuit current of the air-exposed devices was still found to vary systematically with phi(W). This interpretation is supported by UV/Vis investigations as well as electric force microscopy and Kelvin probe measurements of the surfaces of doped and non-doped PEDOT layers, which show very little difference in their surface potential after exposure to air, even though their optical spectra differ significantly. Using this new approach means that it is now possible to dope the PEDOT to high levels (thus maximizing its conductivity) without electrochemically altering the overlying PPV-based polymer layer.