Summary This paper presents a novel strategy to fabricate two-dimensional poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) photonic crystals (PCs) combining electron beam lithography (EBL) and plasma etching (PE) processes. Introduction OLEDs and OPVCs will play a fundamental role in the new frontiers of the OE (Organic Electronic) devices due to the efficiency achievements, the ease in the realization processes, and the possibility of making the devices on flexible substrates. One of the essential points to ensure a future in the development of this technology is the devices quantum efficiency that will give to this device classes a key role in the new frontier of lighting and energy storage. It is widely know that the external quantum efficiency of conventional organic LED devices remain near 20% because of losses due to wave-guiding effect. Recently, there has been great progress to enhance the light out-coupling efficiency of organic electroluminescent devices by means of various internal and external device modification techniques. Several strategies were developed concerning the surface modification to increase the efficiency factor by using ordered micro-lenses, bragg reflectors, 2D photonic crystal or modifying the cavity effects [1-3]. Discussion Here we presents a novel strategy to fabricate two-dimensional poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) photonic crystals (PCs) combining electron beam lithography (EBL) and plasma etching (PE) processes. The surface morphology of PEDOT:PSS PCs after mild oxygen plasma treatment was investigated by scanning electron microscopy (Fig.1). The effects on light extraction are studied experimentally. Vertical extraction of light was found to be strongly dependent on the geometric parameters of the PCs. By changing the lattice type from triangular to square and the geometrical parameters of the photonic structures, the resonance peak could be tuned from a narrow blue emission at 445 nm up to a green emission at 525 nm with a full width at half-maximum of 20 nm, which is in good agreement with Bragg's diffraction theory and free photon band structure. Both finite-difference time-domain and plane wave expansion methods are used to calculate the resonant frequencies and the photonic band structures in the two-dimensional photonic crystals showing a very good agreement with the experiment results. A 2D nanopatterned transparent anode was also fabricated onto a flexible polyethylene terephthalate (PET) substrate and it was integrated into an organic light-emitting diode (OLED). The obtained results fully confirm the feasibility of the developed process of micro/nano patterning PEDOT:PSS. Engineered polymer electrodes prepared by this unique method are useful in a wide variety of high-performance flexible organic optoelectronics. Conclusions In conclusion, we demonstrated the possibility to realize a discontinuous refractive index path directly on the polymeric electrode surface combining EBL and a PE process to partially structure the highly conductive PEDOT:PSS. The low-index grid realized by the presence of PEDOT:PSS could redirect modes normally trapped within the high-index organic layers that will improve the devices efficiency performance. We performed several measurements and simulations to elude the trial and error approach and to analyze the photonic structure according to the analysis of the source spectra, to easier achieve a real enhancement of light extraction. Thus this technique is a potential candidate for the enhancement of light efficiency in OLEDs and will be tested with further investigations also to realize a non conventional OLED-PC devices. References [1] L. Petti, M. Rippa, R. Capasso, G. Nenna, A. De Girolamo Del Mauro, G. Pandolfi, M.G. Maglione, C. Minarini, "Fabrication of novel two-dimensional nanopatterned conductive PEDOT:PSS films for organic optoelectronic applications" ACS Appl. Mater. Interfaces, 5, 4777-4782 (2013) [2] L. Petti, M. Rippa, R. Capasso, G. Nenna, A. De Girolamo Del Mauro, V. La Ferrara, A. Pacheri Madathil, C. Minarini, "Photonic crystal electrode to be used in organic led structures" Journal of the European Optical Society 8, 13002 (2013) [3] L. Petti, M. Rippa, R. Capasso, G. Nenna, A. De Girolamo Del Mauro, M. G. Maglione and C. Minarini "Novel organic LED structures based on a highly conductive polymeric photonic crystal electrode" Nanotechnology 24 (2013)
Polymeric photonic crystal electrode to be used in flexible organic LED structures
Lucia Petti;Massimo Rippa;
2013
Abstract
Summary This paper presents a novel strategy to fabricate two-dimensional poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) photonic crystals (PCs) combining electron beam lithography (EBL) and plasma etching (PE) processes. Introduction OLEDs and OPVCs will play a fundamental role in the new frontiers of the OE (Organic Electronic) devices due to the efficiency achievements, the ease in the realization processes, and the possibility of making the devices on flexible substrates. One of the essential points to ensure a future in the development of this technology is the devices quantum efficiency that will give to this device classes a key role in the new frontier of lighting and energy storage. It is widely know that the external quantum efficiency of conventional organic LED devices remain near 20% because of losses due to wave-guiding effect. Recently, there has been great progress to enhance the light out-coupling efficiency of organic electroluminescent devices by means of various internal and external device modification techniques. Several strategies were developed concerning the surface modification to increase the efficiency factor by using ordered micro-lenses, bragg reflectors, 2D photonic crystal or modifying the cavity effects [1-3]. Discussion Here we presents a novel strategy to fabricate two-dimensional poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) photonic crystals (PCs) combining electron beam lithography (EBL) and plasma etching (PE) processes. The surface morphology of PEDOT:PSS PCs after mild oxygen plasma treatment was investigated by scanning electron microscopy (Fig.1). The effects on light extraction are studied experimentally. Vertical extraction of light was found to be strongly dependent on the geometric parameters of the PCs. By changing the lattice type from triangular to square and the geometrical parameters of the photonic structures, the resonance peak could be tuned from a narrow blue emission at 445 nm up to a green emission at 525 nm with a full width at half-maximum of 20 nm, which is in good agreement with Bragg's diffraction theory and free photon band structure. Both finite-difference time-domain and plane wave expansion methods are used to calculate the resonant frequencies and the photonic band structures in the two-dimensional photonic crystals showing a very good agreement with the experiment results. A 2D nanopatterned transparent anode was also fabricated onto a flexible polyethylene terephthalate (PET) substrate and it was integrated into an organic light-emitting diode (OLED). The obtained results fully confirm the feasibility of the developed process of micro/nano patterning PEDOT:PSS. Engineered polymer electrodes prepared by this unique method are useful in a wide variety of high-performance flexible organic optoelectronics. Conclusions In conclusion, we demonstrated the possibility to realize a discontinuous refractive index path directly on the polymeric electrode surface combining EBL and a PE process to partially structure the highly conductive PEDOT:PSS. The low-index grid realized by the presence of PEDOT:PSS could redirect modes normally trapped within the high-index organic layers that will improve the devices efficiency performance. We performed several measurements and simulations to elude the trial and error approach and to analyze the photonic structure according to the analysis of the source spectra, to easier achieve a real enhancement of light extraction. Thus this technique is a potential candidate for the enhancement of light efficiency in OLEDs and will be tested with further investigations also to realize a non conventional OLED-PC devices. References [1] L. Petti, M. Rippa, R. Capasso, G. Nenna, A. De Girolamo Del Mauro, G. Pandolfi, M.G. Maglione, C. Minarini, "Fabrication of novel two-dimensional nanopatterned conductive PEDOT:PSS films for organic optoelectronic applications" ACS Appl. Mater. Interfaces, 5, 4777-4782 (2013) [2] L. Petti, M. Rippa, R. Capasso, G. Nenna, A. De Girolamo Del Mauro, V. La Ferrara, A. Pacheri Madathil, C. Minarini, "Photonic crystal electrode to be used in organic led structures" Journal of the European Optical Society 8, 13002 (2013) [3] L. Petti, M. Rippa, R. Capasso, G. Nenna, A. De Girolamo Del Mauro, M. G. Maglione and C. Minarini "Novel organic LED structures based on a highly conductive polymeric photonic crystal electrode" Nanotechnology 24 (2013)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
