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Project: MICRO- AND NANOPATTERNING OF CROSS-LINKABLE ELECTRO-ACTIVE POLYMERS BY SPIN-COATING

Acronym: NANOPEPS
Main Objective: This project deals with the optimization of organic electronic devices, namely photovoltaic cells (PV), light-emitting diodes
(LEDs) and optical chemical sensors, through the provement of the organic film morphology and functionality using a low-cost, simple, and innovative method of patterning at the submicrometric or the nanoscale.

Our group was recently pioneer in exploring a simple and low-cost method to prepare patterned films at the submicrometric scale using cross-linkable electroluminescent polymers also synthesised in our group. In principle, the method should be scalable to large substrates and to a broad range of different classes of conjugated polymers. Basically, it consists on controlling the phase separation occurring during the deposition of a solution containing a cross-linkable electro-active polymer and an «inert» polymer, on a substrate, by spin coating. The main original characteritsic of this approach is that the cross-linked film is resistant against dissolution, enabling that multilayer devices may be fabricated utilizing low cost solution techniques. This project proposes i) to synthesise new cross-linkable semiconducting polymers with chemical properties designed for specific applications; ii) to extend and to explore the patterning method to those materials to obtain film morphologies tuned for specific applications iii) to fabricate efficient devices based on such films. The target devices are:
- PV cells. Semiconducting polymer based-films where electron-donor and -acceptor materials are segregated forming vertical
domains (relative to the electrodes) and these are separated from less than 20 nm represent the optimal film
morphology, because it minimizes losses in the charge generation and transport to the electrodes processes. By preparing adequate crosslinkable polymers and using the referred patterning method, we aim at tuning the column dimensions (of columnar films) or porous diameter (of porous films) to obtain ideal nanostructured polymer scaffolds, where the complementary component (donor or acceptor) can afterwards be deposited filling the empty spaces. The resultant arranjement of the two interpenetrating layers should approach the “ideal” morphology for OPV cells.
- Optical Chemical Sensors. Fluorescent semiconducting polymers have shown an amplified response in chemosensing
processes. We intend to functionalize the polymer nanopatterned film to recognise selectively a specific target molecule which acts as a fluorescence quencher, generating an optical sensor. Since nanostructures have a huge surface/volume ratio, an even higher sensitivity is expected. Examples of analytes to investigate are fluoride, cyanide, and iodide anions resultant from toxic gases, and metal ions such as Al3+, Pb 2+, and Ag+.
- LEDs. The most efficient organic LEDs are based on multilayered devices comprising both charge transport layers and emissive layers between the electrodes. Besides showing reasonable efficiencies, such values are still well below the predicted maxima. One approach for optimization, nearly unexplored so far, consists on the use of nanopatterned
hole-transport layers to increase the contact area for charge transfer to the emissive layer. Also, there have been reports
demonstrating higher emission efficiency in nanopatterned films, for which nanopatterning of the emissive layer represents another approach to optimize LEDs.
Reference: PTDC/CTM-NAN/111263/2009
Funding: FCT/PTDC
Start Date: 01-01-2011
End Date: 01-12-2013
Team: Ana Maria de Matos Charas
Groups: Organic Electronics – Lx
Partners:
Local Coordinator: Ana Maria de Matos Charas
Associated Publications