Academic literature on the topic 'Light emitting diodes. Conjugated polymers Fluorene'

This dissertation describes work done to improve the efficiency of conjugated-polymer organic light-emitting diodes (OLEDs) by harvesting both singlet and triplet excitons as electroluminescence. The electroluminescence quantum efficiencies of OLEDs based on the fluorescent conjugated polymer poly(9,9-dioctyl-9<i>H</i>-fluorene-2,7-diyl) 1.08 have been improved through the design, synthesis and application of new phosphorescent conjugated polymers. A study of simple blends of phosphorescent dopants with the polymer 1.08 showed that the red-phosphorescent dopant 2.15 is better suited for observing phosphorescent emission in a blend with the polymer 1.08 than are green- or orange-phosphorescent dopants. (Fig 8453A) The problem of phase separation in the simple blends was solved by tethering the red-phosphorescent dopants to the polyfluorene chains, to give the new phosphorescent conjugated copolymer 3.30. The maximum electroluminescence efficiencies in OLEDs of the copolymer 3.30, are greater than those of the corresponding fluorescent conjugated polymer, and typically an order of magnitude greater than those of the corresponding simple blends. (Fig. 8453B) Dexter triplet-energy transfer reduces the photoluminescence efficiency of copolymers in which the red-phosphorescent dopants are bonded directly to the polyfluorene chains - a nonconjugated manner but without the separation of a tether. In addition, the polymerisation of monomers with small singlet-triplet energy gaps has been proposed as a route for the synthesis of conjugated polymers with small singlet-triplet energy gaps, and some preliminary results are presented.

The initiation of research into conjugated polymer electroluminescent devices in Durham is reported. The apparatus required for the fabrication and characterisation of polymer light-emitting diodes (LEDs) is outlined, and the essential assumptions and calculations required to determine their efficiency, brightness and colour are summarised. Optical and electrical characterisation of a range of polymers is reported, including polypyridine (PPY) and a range derivatives, poly(p-phenylene vinylene) (PPV) and poly(2-methoxy, 5-(2'ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV). The optical properties of PPY in solution, film and dilute solid state are characterised. The conjugation length of PPY is investigated by deliberate disruption of the conjugation by the inclusion meta-links in the otherwise para-linked polymer. The effect of altering the chemical structure of PPY is investigated by the study of some PPY derivatives including random and regular copolymers. The consequences of using precursor polymers, especially the effects of conversion on indium tin oxide coated substrates are investigated using absorption and luminescence spectroscopy and capacitance-voltage analysis. Electroluminescence from a number of conjugated polymers is reported and the efficiency, spectral output and device characteristics are presented. The formation of Schottky barriers in some polymer devices is investigated using quasi-static capacitance-voltage measurements. Improvements in the quantum and power efficiency of polymer LEDs have been achieved using two hole-transporting polymers, poly(vinyl carbazole) and the doped, conducting form of polyaniline. A substantial improvement in quantum efficiency has also been demonstrated when PPY is used as an electron-transporting layer in PPV and MEH-PPV based light-emitting diodes. The variation in quantum efficiency and emission spectrum with the ratio of the thickness of the two polymer layers is reported and analysed.

Conjugated polymers and oligomers are great materials for use in the next generation devices namely organic field effect transistors, light emitting diodes and polymeric solar cells. Apart from having the potential for developing power-efficient, flexible, robust and inexpensive devices, conjugated polymers can also be tuned by molecular design to optimize device characteristics. One key problem for the full commercial exploitation of conjugated polymers is that the charge carrier mobility of the state-of-the-art polymer semiconductors is much lower than required for many applications. The performance of the devices is strongly dependent on the molecular structure and supermolecular assembly of the conjugated polymer chains. This thesis covers our attempts to design molecular structure to control and improve the solid state properties of conjugated polymers. The relative placement of side chains along the backbone has a great influence on the solid state ordering of conjugated polymers. Poly(2,5-disubstituted-1,4-phenylene ethynylene)s (PPE)s, an important class of conjugated polymers, are generally synthesized by Pd-catalyzed coupling polymerizations of appropriately substituted diiodo and diethynyl benzenes (i.e., A-A and B-B type monomers). In asymmetrically substituted PPEs, this results in an irregular substitution pattern of the side chains along the polymer backbone. We report a new synthetic approach to prepare regioregular unsymmetrically substituted PPEs by polymerization of 4-iodophenylacetylenes (i.e., A-B type monomer). We provide a detailed discussion of various approaches to the synthesis of PPEs with different regioregularities and provide a description of the differences between regioregular and regiorandom analogs. The effect of regioregularity becomes even more important when the two side chains are very dissimilar or amphiphilic. We explore the effect of relative placement hydrophobic (dodecyloxy) / hydrophilic (tri(ethylene glycol) and hydrophobic (dodecyloxy)/fluorophilic (fluoroalkyl) side chains along the poly(1,4-phenylene ethynylene) backbone. We found that the regioregular substitution of the polymer backbone provides a structure in which the side chains segregate to afford a Janus-type structure. The regioregular polymer chains pack more densely in a monolayer at the air-water interface, and pack into a bilayer in the solid state to form a highly crystalline material. Pentacenes are very important organic molecules for use as semiconductor in oFETs due to their low band gap and high field effect mobility. One approach to reduce the bandgap of a polymeric system and improve performance is to include low bandgap small molecules into the conjugated backbone. A new copolymer system consisting of pentacene and terthiophene was developed and its optical and electronic properties along with its stability were evaluated. We report the use of ultrasonication of P3HT as a novel operationally-simple process to significantly improve the field effect mobility of P3HT-based FETs, thereby potentially eliminating the need for dielectric surface modifications or further processing of the device. Investigation of the sonicated polymer samples by number of characterization techniques indicates that ultrasonication leads to aggregation and ordering of the P3HT chains resulting in increase in the mobility.

The synthesis and optoelectronic properties of biphenyl based conjugated copolymers with varying acceptor units in the polymer backbone were investigated. The well known Donor-Acceptor Theory was used to establish the synthetic pathway for the structural modifications. Solubility issues regarding biphenyl polymer was solved by copolymerizing with soluble units. For this purpose<br>poly 4-(biphenyl-4-yl)- 4&rsquo<br>-tert butylspiro[benzo[d]imidazole-2,1&rsquo<br>-cyclohexane] (P1), poly 4-(biphenyl-4-yl)- 2- dodecyl-2H-benzo[d][1,2,3]triazole (P2) and poly(4-(5-(biphenyl-4-yl)-4-hexylthiophen- 2-yl)-2-dodecyl-7-(4-hexylthiophen-2-yl)-2H-benzo[d][1,2,3]triazole (P3) were synthetized using Suzuki coupling process. Electrochemical properties of these polymers were examined by cyclic voltammetry, spectroelectrochemistry and kinetic studies. Polymers P2 and P3 showed both p- and n-doping behaviors and multicolored electrochromic states. Optical studies revealed that emission color of biphenyl is tuned from blue to orange and the polymers are good candidates for light emitting diode applications. OLED application of P3 was established and outputs of the device were increased by energy transfer studies. The preliminary investigation indicated that P3 possesses promising efficiencies.

碩士<br>國立中央大學<br>化學研究所<br>93<br>Abstract: A series of novel light-emitting copolymers derived from spiro-fluorene-acridine and spiro-bifluorene, are prepared by palladium-catalyzed Suzuki coupling reaction.Spiro-fluoreneacridine have rigid structure so copolymers show high Tg and it can also be utilized as hole-transporting material.These polymers have good solubility in common organic solvents, such as 1,2-dichlorobenzene, CH2Cl2, THF, toluene, and o-xylene.DSC and TGA studies reveal that novel polymers possess excellent thermal stability with high glass transition temperatures (Tg >300oC).Blue light-emitting device (Glass/ITO(120nm)/PEDOT：PSS(65nm)/ACOXP6(60nm)/Ca(30nm)/Al(130nm)) ， showed maximal externalquantum efficiency of 0.557% and the highest brightness of 977 cd/m2,and CIE(0.17,0.09). Red light-emitting device (Glass/ITO(120nm)/PEDOT：PSS(80nm)/ACTBP5(120nm)/LiF(0.7nm)/Al(130nm))，showed maximal external quantum efficiency of 1.497% and the highest brightness of 4667 cd/m2, and CIE(0.65,0.34). Green light-emitting device (Glass/ITO(120nm)/PEDOT：PSS(50nm)/ACTBP6(120nm)/Ca(30nm)/Al(130nm)) showed maximal external quantum efficiency of 0.849% and the highest brightness of 13874cd/m2, and CIE(0.37,0.58).Yellow light-emitting device (Glass/ITO(120nm)/PEDOT：PSS(65nm)/IrP2(60nm)/LiF(0.7nm)/Al(130nm)) showed maximal external quantum efficiency of 1.153% and the highest brightness of 671cd/m2, and CIE(0.47，0.52).