Nanoscale heterogeneity and light-emission dynamics in solution-processed phosphorescent organic light-emitting devices

Sekiguchi, Yasuhiro; Habuchi, Satoshi; Vácha, Martin

doi:10.1039/b913401h

Cited by 3 publications

(3 citation statements)

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“…This goal has been already achieved by optically pumping a single molecule in a solid 104 but a very promising alternative is to excite a single molecule with charges injected in the host material, by an electroluminescence process. [105][106][107][108][109] An organic light-emitting diode (OLED) structure which was recently used to activate and resolve the emission of single molecules 106 consists of an anode (indium tin oxide, ITO, deposited on a cover slide), a hole-transporting layer, a photonemitting layer, which itself consists of a hole-transporting polymer co-doped with the electron-transporting material and a phosphorescence emitter, and a metallic cathode. When voltages are applied to the electrodes, the injected hole can be trapped close to the phosphorescent molecule, Ir(ppy) 3 , and can capture an electron to create an exciton.…”

Section: External Field and Injected-charge Effects On Single Moleculesmentioning

confidence: 99%

“…110,111 The first experiments performed using optical microscopy with polymer-based phosphorescent OLEDs pointed to voltage-dependent spatial and temporal heterogeneities in the emission of individual molecules, which follow the dynamics of structural inhomogeneity of the host, the charge-transporting polymer matrix. [106][107][108] It may be expected that further research on electroluminescence at nanometer scales will lead to better procedures for elaborating polymer layers and to new compositions for OLED devices. 109…”

Section: External Field and Injected-charge Effects On Single Moleculesmentioning

confidence: 99%

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Single-molecule photophysics, from cryogenic to ambient conditions

Kozankiewicz

Orrit

2014

Chem. Soc. Rev.

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We review recent progress in characterizing and understanding the photophysics of single molecules in condensed matter, mostly at cryogenic temperatures. We discuss the central role of the triplet state in limiting the number of useful host-guest systems, notably a new channel, intermolecular intersystem crossing. Another important limitation to the use of single molecules is their photo-reactivity, leading to blinking of the fluorescence signal, and eventually to its loss by photo-bleaching. These processes are at the heart of modern super-resolution schemes. We then examine some of the new host-guest systems recently discovered following these general principles, and the mechanisms of spectral diffusion and dephasing that they have revealed. When charges are injected into organic conductors, they get trapped and influence single molecules via the local fields they create in the material, and via their coupling to localized vibrations. Understanding these processes is necessary for better control of spectral diffusion and dephasing of single molecules. We finally conclude by giving some outlook on future directions of this fascinating field.

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Section: External Field and Injected-charge Effects On Single Moleculesmentioning

confidence: 99%

Section: External Field and Injected-charge Effects On Single Moleculesmentioning

confidence: 99%

Single-molecule photophysics, from cryogenic to ambient conditions

Kozankiewicz

Orrit

2014

Chem. Soc. Rev.

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“…response is given by the time it takes to scan an image, and for which individual component layers of the device have to be exposed to the probe in order for the measurement to be carried out. The technique has recently been used to study nanoscale heterogeneities in non-conjugated polymer based OLEDs, 14 and its sensitivity ultimately enables the detection of EL from single molecules. 15 The devices used in this work are prepared directly on microscope cover slips.…”

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confidence: 99%

Nanoscale dynamic inhomogeneities in electroluminescence of conjugated polymers

Hatano¹,

Nozue²,

Habuchi³

et al. 2011

Journal of Applied Physics

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We report the observation and characterization of dynamic spatial heterogeneities in the electroluminescence (EL) of conjugated polymer organic light-emitting diodes via high-sensitivity fluorescence microscopy. The active layers of the single-layer devices are polymers of the poly (phenylene vinylene) family, i.e., poly[2-methoxy, 5-(2 0 -ethyl-hexyloxy)-p-phenylene vinylene] and a commercially available copolymer, Super Yellow. The devices are prepared directly on a microscope coverslip, making it possible to use high numerical aperture oil-immersion objective lenses with a diffraction-limited resolution of a few hundred nanometers for microscopic EL imaging. Detection via high-sensitivity CCD camera allows the measurement of EL dynamics with millisecond time resolution for a wide range of applied voltages. We found spatial heterogeneities in the form of high EL intensity sites in all devices studied. The EL from these sites is strongly fluctuating in time, and the dynamics is bias voltage dependent. At the same time, there is no difference in the local microscopic EL spectra between the high-and low-intensity sites. The results are interpreted in terms of a changing charge balance and local structural changes in the active film layer.

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