White Light Electrophosphorescence from Polyfluorene-Based Light-Emitting Diodes: Utilization of Fluorenone Defects†
12 May 2004-Journal of Physical Chemistry B (American Chemical Society)-Vol. 108, Iss: 25, pp 8601-8605
TL;DR: In this paper, a white electrophosphorescent light-emitting diodes were fabricated using fluorenone defects in poly(9,9-dioctylfluoren2,7-diyl), PFO.
Abstract: Poly(9,9-dioctylfluorene-co-fluorenone) with 1% fluorenone, (PFO-F(1%)), was synthesized as a model compound to investigate the optical and electrical effects of fluorenone defects in poly(9,9-dioctylfluoren2,7-diyl), PFO. Photoluminescence (PL) and electroluminescence (EL) measurements demonstrate that PFO-F(1%) emits stable green light. PL and EL studies indicate that Forster energy transfer to and charge carrier trapping on fluorenone defects (with subsequent fluorenone emission) are responsible for the color degradation typically observed with the polyfluorenes. By utilization of "fluorenone defects" in PFO-fluorenone copolymers (PFO-F), white electrophosphorescent light-emitting diodes were fabricated. Polymer blends were spin-cast from solution containing PFO, PFO-F (1%), and tris[2,5-bis(9,9-dihexylfluoren-2-yl)pyridine-κ 2 NC 3 ]iridium-(III), Ir(HFP) 3 . The white emission turns on at approximately 5 V, with a luminance (L) of 6100 cd/m 2 at 17 V. The luminous efficiency is 3 cd/A at current density of 8.5 mA/cm 2 (L = 255 cd/m 2 ). The white light exhibits stable color coordinates and stable color temperature and has a high color rendering index.
Citations
More filters
TL;DR: This review highlights recently developed bipolar host materials with the focus on molecular design strategies and the structure-property-performance relationships of various classes ofipolar host materials, which are classified into several categories according to the structural features of their constituents (HT/ET blocks and spacers).
Abstract: The future of organic light-emitting devices (OLEDs) is drifting from electrofluorescence toward electrophosphorescence due to the feasibility of realizing 100% internal quantum efficiency. There is limited availability of transition metals (TMs) such as Ir, Os, and Pt, which are used for color-tunable phosphorescent emitters, and the use of the host-guest strategy is necessary for suppressing the detrimental triplet-triplet annihilation inherently imparted by the TM-centered emitters. The inevitable demands of organic host materials provide organic chemists with tremendous opportunities to contribute their expertise to this technology. With suitable molecular design and judicious selection of chemical structures featured with different electronic nature, the incorporation of hole-transporting (HT) and electron-transporting (ET) moieties combines the advantages of both functional units into bipolar host materials, which perform balanced injection/transportation/recombination of charge carriers and consequentially lead the OLEDs to have higher performances and low roll-off efficiencies. This review highlights recently developed bipolar host materials with the focus on molecular design strategies and the structure-property-performance relationships of various classes of bipolar host materials, which are classified into several categories according to the structural features of their constituents (HT/ET blocks and spacers).
480 citations
Abstract: A novel series of semiconducting conjugated copolymers, derived from alkyl-substituted fluorene, 4,7-diselenophen-2‘-yl-2,1,3-benzothiadiazole (SeBT), and 4,7-diselenophen-2‘-yl-2,1,3-benzoselenadiazole (SeBSe), was synthesized by a palladium-catalyzed Suzuki coupling reaction with various feed ratios. The optical band gap of copolymers is very low, 1.87 eV for SeBT and 1.77 eV for SeBSe. The efficient fast energy transfer from fluorene segments to narrow-band-gap sites was observed. The emission of photoluminescence and electroluminescence is dominated by narrow-band-gap species and peaked at 670−790 nm, in the range from deep-red to near-infrared (NIR). The external electroluminescent (EL) quantum efficiencies reached 1.1% and 0.3% for devices from these two types of copolymers, respectively. Bulk−heterojunction polymer photovoltaic cells (PPVCs) made from composite thin film of the copolymer 9,9-dioctylfluorene and SeBT (PFO−SeBT) in blend with fullerene derivative [6,6]-phenyl C61 butyric acid methyl ...
372 citations
TL;DR: In this article, a polyfluorene-type blue-emitting conjugated polymer doped with green and red phosphorescent dyes was used to obtain a white emission spectrum.
Abstract: Efficient white-light-emitting diodes (WLEDs) have been developed using a polyfluorene-type blue-emitting conjugated polymer doped with green and red phosphorescent dyes. The emission spectrum of the conjugated polymer, which has a very high luminescent efficiency, shows a large spectral overlap with the absorbance of green and red iridium complexes. Also, efficient energy transfer from the conjugated polymer to the iridium complexes is observed. Poly(N-vinyl carbazole) is used to improve the miscibility between conjugated polymer and iridium complexes because of their poor chemical compatibility and phase separation. A white emission spectrum is easily obtained by varying the contents of the three materials and controlling the phase morphology. Moreover, these WLEDs show a voltage-independent electroluminescence owing to the threshold and driving voltage of the three materials being similar as a result of energy transfer.
146 citations
TL;DR: In this paper, the authors give a simple introduction to the electronic, optical and structural behavior of rod-coil block copolymers in which the rod block is conjugated.
Abstract: This review gives a simple introduction to the electronic, optical and structural behaviour of rod-coil block copolymers in which the rod block is conjugated The current understanding of the optical properties of conjugated polymers is discussed, as is the self-assembly characteristics of rod-coil block copolymers, along with their behaviour with respect to organic light-emitting diode and photovoltaic devices Poly(p-phenylene), poly(p-phenylenevinylene) and polythiophenes are then used to give concrete examples and a short history of the developments of this astounding field (C) 2010 Society of Chemical Industry
95 citations
References
More filters
TL;DR: In this article, the authors reported visible light emission from Shottky diodes made from semiconducting polymers, confirming the discovery by the Cambridge group [Nature 347, 539 (1990)].
Abstract: We report visible light emission from Shottky diodes made from semiconducting polymers, confirming the discovery by the Cambridge group [Nature 347, 539 (1990)]. Our results demonstrate that light‐emitting diodes can be fabricated by casting the polymer film from solution with no subsequent processing or heat treatment required. Electrical characterization reveals diode behavior with rectification ratios greater than 104. We propose that tunneling of electrons from the recitifying metal contact into the gap states of the positive polaron majority carriers dominates current flow and provides the mechanism for light emission.
2,038 citations
TL;DR: In this paper, the authors focus on reliable structure-property relationships regarding substitution pattern, solid state morphology, and optical/electronic properties, and the key role of degradation-induced keto defect sites in fluorerse-type polymers and strategies for obtaining defect-free polyfluorenes.
Abstract: Alkylsabstituted polyfluorenes have emerged as a very attractive class of conju gated polymers, especially for display applications, owing to their pure blue and efficient electroluminescence coupled with a high charge-carrier mobility and good processability. The availability of specific and highly regroselective coupling reactions provides a rich variety of taifored polyfluorene-type paly mers and copolymers. The focus of this review, therefore, is on reliable structure-property relationships regarding (i) the interplay of substitution pattern, solid state morphology, and optical/electronic properties, and (ii) the key role of degradation-induced keto defect sites in fluorerse-type polymers, and strategies for obtaining defect-free polyfluorenes.
1,557 citations
TL;DR: When asked to explain the importance of the discovery of conducting polymers, I offer two basic answers: first they did not (could not?) exist, and second, that they offer a unique combination of properties not available from any other known materials.
Abstract: When asked to explain the importance of the discovery of conducting polymers, I offer two basic answers: first they did not (could not?) exist, and second, that they offer a unique combination of properties not available from any other known materials. The first expresses an intellectual challenge; the second expresses a promise for utility in a wide variety of applications.
1,497 citations
TL;DR: This paper review in more detail related work that originated at IBM during the last four years and has led to the fabrication of high-performance organic transistors on flexible, transparent plastic substrates requiring low operating voltages.
Abstract: In this paper we review recent progress in materials, fabrication processes, device designs, and applications related to organic thin-film transistors (OTFTs), with an emphasis on papers published during the last three years. Some earlier papers that played an important role in shaping the OTFT field are included, and a number of previously published review papers that cover that early period more completely are referenced. We also review in more detail related work that originated at IBM during the last four years and has led to the fabrication of high-performance organic transistors on flexible, transparent plastic substrates requiring low operating voltages.
1,192 citations
TL;DR: In this article, the important materials issues are reviewed and the prospects for making polymer diode lasers are discussed, as well as the possible applications of polymer polymers in light-emissive laser materials.
Abstract: Light-emissive polymers are outstanding laser materials because they are intrinsically “4-level” systems, they have luminescence efficiencies higher than 60 % even in undiluted films, they emit at colors that span the visible spectrum, and they can be processed into optical quality films by spin casting. The important materials issues are reviewed and the prospects for making polymer diode lasers are discussed.
831 citations