Mohamed Bouguettaya

Near-infrared electroluminescence from conjugated polymer/lanthanide porphyrin blends

Near-infrared-emitting polymer light-emitting diodes (PLEDs) have been fabricated using blends of conjugated polymers and lanthanide tetraphenylporphyrin complexes. Host polymers include MEH–PPV and a bis-alkoxy-substituted poly(p-phenylene) (PPP–OR11), and the lanthanide complexes include Yb(TPP)acac and Er(TPP)acac (where TPP=5,10,15,20-tetraphenylporphyrin and acac=acetylacetonate). Electroluminescence (EL) is observed at 977 nm from devices fabricated using MEH–PPV or PPP–OR11 blended with Yb(TPP)acac, and EL is observed at 1560 nm from a device fabricated using a blend of MEH–PPV and Er(TPP)acac. Visible EL from the host polymers is strongly suppressed in all of the devices, however, in the device fabricated using the PPP–OR11 polymer blue emission from the host is completely quenched. Very efficient quenching of the EL from the host in the PPP–OR11 device is believed to occur due to efficient Forster energy transfer, which is facilitated by the excellent spectral overlap between the PPP–OR11 fluores...

Near-infrared organic light emitting diodes

Near-IR emitting organic light emitting diodes that contain an active material consisting of a blend of a poly(paraphenylene) and Ln-porphyrins are prepared and characterized.

Solution Processed Conjugated Polymer Multilayer Structures for Light Emitting Devices

We study the feasibility of semiconducting polymer nanospheres deposited from miniemulsions as an approach to form organic multilayer structures and devices from an all solution based process. A detailed study of the wetting and film forming properties of the dispersed semiconducting polymer nanospheres on different polar and non-polar organic surfaces is given. The transmission and fluorescence properties of the polymer multilayer structures are studied. Organic light emitting devices based on such multilayer structures are presented and their properties are discussed.

Elimination of defect-induced color instabilities in polymer light-emitting devices

We demonstrate that utilizing a blue light-emitting oligo(ethylene oxide)-grafted conjugated poly(p-phenylene) (PPP-OR11) as an active layer in a light-emitting electrochemical cell (LEC) preserves a color-stable blue light emission. This is in contrast to the polymer light-emitting diodes (PLEDs) constructed using the same emitting polymer without ionic species, which exhibits a rapid red shifting of the emission to a distinct green. We attribute the color shift to various degradation processes caused by oxidative degradation and aluminum deposition-induced defects in PPP-OR11. The analysis of the degradation processes in the PLEDs shows that the color stability in the LEC is caused by a controlled shift of the recombination zone from the defects including cathode∕polymer interface to an undoped intrinsic zone between the p- and n-type regions of the active layer in the LECs, which qualifies the LEC type devices as a cost-effective approach to the single layer color-stable blue emitting devices.

Interface and ion-induced optoelectronic effects in thin films of poly(p-phenylene)s functionalised with ion-transporting side chains

Abstract We report on investigations of thin films of homopolymers and copolymers consisting of a conjugated poly(p-phenylene) (PPP) backbone and oligo(ethylene oxide) (OEO) side chains of varying chain length in order to supply a conjugated backbone with an ion-transporting functionality. The optical properties of these polymeric mixed ionic–electronic conductors (PMIECs) reveal a response upon complexation of the OEO side chains with an alkali metal salt (lithium triflate). In addition, the rather polar nature of the OEO side chains and the non-polar nature of the PPP backbone can be applied to control the polymer/substrate interfacial properties. These topics were investigated by means of UV/VIS/NIR absorption measurements, along with photoinduced absorption spectroscopy. Infrared and Raman spectroscopy complemented this work to determine the amount of ion dissociation.

Tracking ion mediated changes in the optical properties of a polymeric mixed ionic–electronic conductor: an application for a chemical sensor system

Abstract In this study, we use photoinduced absorption (PIA) spectroscopy to show that the triplet exciton properties of an oligo(ethylene oxide) (OEO) grafted conjugated polymer (PPP-R10) are very sensitive to the presence of ionic species. Investigations were performed on thin spin-cast films of this polymeric mixed ionic–electronic conductor. Since the ion-coordinating side-chains are directly attached to the conjugated backbone, an ion induced order–disorder transition affects the characteristics of the conjugated polymer, which is observable as a blue shift in the π–π * absorption, the triplet exciton absorption spectra, and also manifests in other triplet exciton properties, like their lifetimes and the bimolecular annihilation parameter. Based on the sensitivity of the triplet exciton properties such polymers can be envisioned in the application in chemical sensor systems.

Photophysics and optoelectronic properties of a poly(p-phenylene)-type polymer in different kinds of light-emitting devices

We report on the photophysics of the pristine oligo(ethylene oxide) side-chain grafted polymer PPP-OR11 and the polymer blended with the lithium salt lithiumtriflate. The side-chains render the polymer soluble in common organic solvents and in addition provide ionic conductivity, which is important for the application of the polymer as mixed ionic-electronic conductor for instance in light-emitting electrochemical cells (LECs). The optoelectronic properties of the polymer were studied for two types of light-emitting devices, first in light emitting diodes and secondly in LECs. From these investigations it is evident that in polymer light-emitting diodes (PLEDs) several degradation processes caused by defects on the PPP backbone deteriorate the color stability. These defects are induced either by the oxidation of the polymer or the aluminum deposition process upon device fabrication. Contrarily, LECs fabricated from the same polymer provide color stable blue emission. The color stability of the LEC can be explained by the fact that the recombination zone is shifted from the cathode/polymer interface in PLEDs to the non-doped intrinsic zone between the p- and n-type regions of the LEC, avoiding emission from aluminum evaporation induced defects.