Layer-by-layer nanoarchitecture of ultrathin films assembled of PEDOT-PSS and PPy to act as hole transport layer in polymer light emitting diodes and polymer transistors

Abstract

In this paper we report a controlled architectural growth of ultrathin films of conducting polymers via Layer-by-Layer (L-b-L) self-assembly with poly(3,4-ethylenedioxythiopbene) poly(styrenesulfonate) (PEDOT-PSS) and polypyrrole (PPy) as alternating layers. A typical step of the film growth was 2.3±0.1 nm for every other bilayer. Linear growth of thin films has been observed by annealing each layer, while super-assembly was observed without annealing. The conductivities obtained range from 0.037 S/cm at room temperature to 0.13 S/cm at 120°C. The improved conductivity may be attributed to either: (a) the increase in mobility of charged carriers due to less carrier scattering in the self-assembled layer, or (b) the increased inter-chain hopping between two polymers due to closely packed polymer-chains. The charged carriers in the Hole Transport Layer (HTL) increase the recombination rate of electrons and holes in the electroluminescent layer thus increasing the external quantum efficiency of the Polymer Light Emitting Diodes (PLEDs). Also this confinement of holes is expected to improve the overall performance of polymer thin film transistors.