Achieving full-color organic light-emitting devices for lightweight, flat-panel displays

Jain

Journal of Applied Physics

et al. 2009

Current-voltage ͑J-V͒ characteristics of an organic bulk heterojunction solar cell have been modeled and compared with the measured characteristics of solar cell based on the blend of poly͑3-hexylethiophene͒ ͑P3HT͒ and phenyl ͓6,6͔ C 61 butyric acid methyl ester ͑PCBM͒. In an undoped organic double Schottky junction diode, for V Ͻ V bi the electric field remains constant and is given by ͑V bi − V͒ / d, where V bi is the built-in voltage, V is the applied voltage, and d is sample thickness. We considered the effect of this constant electric field on the charge carrier transport and solved the drift and diffusion equations to model the J-V characteristics. For V Ͻ V bi the current is found to be dominated by diffusion. A comparison of the theoretical results with the experimental data measured in dark and under different illumination intensities shows good agreement.

Section: Introductionmentioning

confidence: 99%

A model for the J-V characteristics of P3HT:PCBM solar cells

Jain

Journal of Applied Physics

et al. 2009

“…This results from emission from a ligand centered π, π* excited state, formed in the transition of an electron from a highest occupied molecular orbital (MO) lying mainly on the phenoxide ring to a lowest unoccupied MO predominantly on the nitrogen atom. 2 By doping with the appropriate dyes, the emission can be tuned through the visible spectrum, 3,4 leading to the possibility of full color OLED displays. The basic processes involved are reasonably well understood, 5,6 with electroluminescence involving generation of singlet excitons from electron-hole recombination.…”

mentioning

confidence: 99%

Characterization of the Triplet State of Tris(8-hydroxyquinoline)aluminium(III) in Benzene Solution

et al. 2003

Since Tang and VanSlyke first reported efficient electroluminescence from a device based on tris(8-hydroxyquinoline)aluminium(III) (Alq 3 ) as the luminescent layer, 1 organic light-emitting diodes (OLEDs), based on these materials, are now at the stage where they are being used as monochrome displays. This results from emission from a ligand centered π, π* excited state, formed in the transition of an electron from a highest occupied molecular orbital (MO) lying mainly on the phenoxide ring to a lowest unoccupied MO predominantly on the nitrogen atom. 2 By doping with the appropriate dyes, the emission can be tuned through the visible spectrum, 3,4 leading to the possibility of full color OLED displays. The basic processes involved are reasonably well understood, 5,6 with electroluminescence involving generation of singlet excitons from electron-hole recombination. From spin statistics, theoretical calculations, and experiment, 7 the singlet:triplet exciton ratio is 1:3, limiting the maximum internal OLED efficiency from fluorescent materials to e25%. Nevertheless, by doping with heavy atom-containing complexes, such as platinum(II) octaethylporphyrin (PtOEP), it is possible to capture triplet excitons (or charge carriers) to give electrophosphorescence, increasing internal quantum yields dramatically. 8 Although of interest for display applications, efficient exploitation requires detailed knowledge of the properties of the lowest triplet state of Alq 3 , which is not available. We are reporting here what we believe to be the first detailed characterization of this state.There is relatively little detailed information on Alq 3 photophysics. Various values have been reported for the fluorescence quantum yield 3,9,10 and lifetime, 3,11 and only indirect information exists on the triplet state. 12,13 Attempts to observe phosphorescence have proved unsuccessful, 11,12 although some information has been inferred from data on heavy metal quinolates. 11 We have shown 14 that pulse radiolysis of benzene solutions selectively produces triplet states of conjugated organic polymers by energy transfer from appropriate sensitizers following pulse radiolysis of benzene solutions. The triplet state of Alq 3 is characterized in the same way.Following pulse radiolysis 15 of an Ar saturated solution of Alq 3 (2.25 × 10 -4 M) and biphenyl (0.01 M) in benzene, the absorption of the biphenyl triplet state 16 was observed, with a maximum below 380 nm. This decayed within a few microseconds to be replaced by a new absorption maximum around 510 nm (Figure 1). This is similar to spectra reported by Ballardini et al. 11 for triplet states of various heavy metal 8-quinolinol chelates and is assigned to the Alq 3 triplet state, which decayed by good first-order kinetics with a lifetime τ ) 56.3 ( 0.4 µs. From the analysis of transient diffusion measurements in doped films, 12 a lifetime of 25 ( 15 µs was estimated for this triplet state. In contrast, a value of ca. 10 ms was reported from delayed luminescence measurements on polycrystall...

IEEE Commun. Surv. Tutorials

“…Exhibiting the dual function of illumination and data transmission, the advantages of LEDs are multi-fold, such as low heat generation [23], low power consumption [24], high energy conversion efficiency/luminous efficacy [25] as well as a potentially high bandwidth [26], etc. Diverse types of LEDs have been developed, which are available in commercial markets, including phosphor converted LEDs (PC-LEDs) [27], multi-chip LEDs (MC-LEDs) [28], organic LEDs (OLEDs) [29] and micro-LEDs [30].…”

Section: Vlc Linksmentioning

confidence: 99%

Optimization of Visible-Light Optical Wireless Systems: Network-Centric Versus User-Centric Designs

Zhang

Hanzo

2018

Abstract-In order to counteract the explosive escalation of wireless tele-traffic, the communication spectrum has been gradually expanded from the conventional radio frequency (RF) band to the optical wireless (OW) domain. By integrating the classic RF band relying on diverse radio techniques and optical bands, the next-generation heterogeneous networks (HetNets) are expected to offer a potential solution for supporting the ever-increasing wireless tele-traffic. Owing to its abundant unlicensed spectral resources, visible light communications (VLC) combined with advanced illumination constitute a competent candidate for complementing the existing RF networks. Although the advantages of VLC are multi-fold, some challenges arise when incorporating VLC into the classic RF HetNet environments, which may require new system architectures. The user-centric (UC) design principle for VLC environments constitutes a novel and competitive design paradigm for the super dense multi-tier cell combinations of HetNets. The UC concept may be expected to become one of the disruptive techniques to be used in the forthcoming fifthgeneration era. This paper provides a comprehensive survey of visible-light-aided OW systems with special emphasis on the design and optimization of VLC networks, where the radically new UC design philosophy is reviewed. Finally, design guidelines are provided for VLC systems.