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Patterning PEDOT:PSS and tailoring its electronic properties by water-vapour-assisted nanoimprint lithography

In this article a new water-vapour-assisted nanoimprint lithography (NIL) process for the patterning and electronic property control, of the conducting poly-ethylenedioxythiophene : poly-styrenesulfonate (PEDOT:PSS) is presented. PEDOT:PSS is a conductive polymer, widely used for organic thin-film  transistors  (OTFTs), organic light-emitting diode (OLED) displays and in organic photovoltaic device (OPV). It has been also demonstrated as catalytically active anti-corrosion electrode in photoelectrochemical cells, in ionic charge storage medium for super capacitors, or as stable, biocompatible, implantable electrodes for in vivo neuronal activity recording. For most of those application nano structuration of the PEDOT:PSS layer is of key importance for device miniaturization and performance. 
 NIL process is a strong candidate for low cost high throughput technique for PEDOT:PSS nano structuration but with traditional NIL process results with limited aspect ratios were obtained (Max 0,86 AR for sub-100nm resolution). The process here presented was optimized with respect to relative humidity, applied pressure and temperature (RH, P, T). The control of environmental humidity was found to be crucial. 

High quality nanostructures were reproducibly obtained at high relative humidity values (RH >75%), with sub-100 nm resolution features attaining aspect ratios (AR) as high as ~6 at ~95% RH. The developed process of water-vapour-assisted NIL (WVA-NIL) strongly affects the electronic properties of PEDOT:PSS. 
By current-voltage measurements and ultraviolet photoemission spectroscopy we demonstrate that the process parameters p, T and RH are correlated with changes of PEDOT:PSS conductivity, work function and states of the valence band. In particular, an increase in the films conductivity by factors as high as 105 and a large decrease in the work function, up to 1.5 eV, upon WVA-NIL processing were observed. Moreover, it was found that workfunction shift can be reversed by a short oxygen plasma treatment, without altering significantly the layer's nano structure or conductivity. Employing the produced PEDOT:PSS nanostructured layers as anode buffer layer in P3HT:ICBA bulk heterojunction solar cells, a significant performance increase was obtained (60% relative increase of  efficiency respect to a not patterned reference cell).


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Patterning PEDOT:PSS and tailoring its electronic properties by water-vapour-assisted nanoimprint lithography

Andrea Radivo,ab   Enrico Sovernigo,ac   Marco Caputo,d  Simone Dal Zilio,a   Tsegaye Endale,e   Alessandro Pozzato,c  Andrea Goldonid and   Massimo Tormen*ac  
*Corresponding authors
a Istituto Officina dei Materiali-CNR, Laboratorio TASC, I-34149 Trieste, Italy
b University of Trieste, Piazzale Europa, I-34127 Trieste, Italia
c ThunderNIL srl, via Ugo Foscolo 8, 35131 Padova, Italy
d Sincrotrone Trieste SCpA, I-34149 Trieste, Italy
e Department of Chemistry, Addis Ababa University, P. O. Box: 1176, Addis Ababa, Ethiopia 

E-mail: tormen@iom.cnr.it ;Tel: +39 0403758416

RSC Adv., 2014,4, 34014-34025
DOI: 10.1039/C4RA04807E
Received 21 May 2014, Accepted 23 Jul 2014
First published online 23 Jul 2014

Last Updated on Monday, 29 September 2014 18:21