Characterization of Quantum Dot/Conducting Polymer Hybrid Films and Their Application to Light‐Emitting Diodes

Kwak, Jeonghun; Bae, Wan Ki; Zorn, Matthias; Woo, Heeje; Yoon, Hyunsik; Lim, Jaehoon; Kang, Sang Wook; Weber, Stefan A. L.; Butt, Hans‐Jürgen; Zentel, Rudolf; Lee, Seonghoon; Char, Kookheon; Lee, Changhee

doi:10.1002/adma.200902072

Cited by 91 publications

(97 citation statements)

References 27 publications

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“…The observed luminance intensity of QD-OLED is comparable with the reported high performance QD-OLED. 4 The luminescence intensity was around 1000 Cdm -2 at around 1x10 -2 A/cm 2 current density. The L-I curve of an OLED without QD at room temperature is also plotted for comparison.…”

Section: Resultsmentioning

confidence: 99%

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Fabrication of high efficient organic/CdSe quantum dots hybrid OLEDs by spin-coating method

Uddin

Teo

2013

SPIE Proceedings

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The cadmium selenite (CdSe) quantum dots (QDs) have promising applications in display technology since its luminescence wavelength can be tuned precisely from blue to red by changing the diameter of the core from 2.0 to 7.0 nm. A self-assembled monolayer of QDs, sandwiched between two organic thin films is necessary to isolate the luminescence processes from charge conduction. The use of QDs for device technology, one of the fundamental issues is how to distribute QDs uniformly on patterned surfaces with precise control of density. In this study, we demonstrate that uniform distribution of QDs with controllable density can be achieved using the conventional spin-coating method. We have fabricated high efficient QD-OLED by spin-coating method. The estimated QDs threshold concentration was found ~ 9x10 11 cm -2 for the best performance of QD-OLED. The AFM morphological studies of the hybrid device showed the formation of a disordered QD film as a result of the aggregation of CdSe/ZnS QDs upon phase segregation. The analysis of electroluminescence (EL) and photoluminescence (PL) performance of OLED showed that precise control of the QD concentration is necessary to maximize the coverage of QDs on organic surface which is an important factor in color tuning. The peak energies of the EL and PL showed only small spectral shifts and no significant dependence on the QDconcentration. The QD emission was increased about three times by annealing of QD-OLED.

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Section: Resultsmentioning

confidence: 99%

“…1,4,5 The charge conductivity of closely packed QDs film is poor, making inefficient electrical pumping of QD. 6 A single self-assembled QDs monolayer, sandwiched between two organic thin films is necessary to isolate the luminescence processes from charge conduction.…”

Section: Introductionmentioning

confidence: 99%

Fabrication of high efficient organic/CdSe quantum dots hybrid OLEDs by spin-coating method

Uddin

Teo

2013

SPIE Proceedings

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“…To date, generally amine, 60 carboxyl, 40 and thiol 62,63 groups (see Table 1) have been used in the functionalized CPs as the anchor groups. This type of hybridization will be promising for future hybrid organic− inorganic optoelectronic systems.…”

Section: The Journal Of Physical Chemistry Lettersmentioning

confidence: 99%

“…This low density was intentionally set to prevent possible phase segregation, which is a common phenomenon in the blended CP−QD films. 26,40,62,63 At increased QD densities in a polymer matrix, the QDs will form micron-scale aggregates in this polymer matrix. The phase segregation is detrimental against efficient nonradiative energy transfer because the donor CPs and the acceptor QDs are physically separated.…”

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confidence: 99%

Organic–Inorganic Composites of Semiconductor Nanocrystals for Efficient Excitonics

Güzeltürk

Demir

2015

J. Phys. Chem. Lett.

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Nanocomposites of colloidal semiconductor nanocrystals integrated into conjugated polymers are the key to soft-material hybrid optoelectronics, combining advantages of both plastics and particles. Synergic combination of the favorable properties in the hybrids of colloidal nanocrystals and conjugated polymers offers enhanced performance and new functionalities in light-generation and light-harvesting applications, where controlling and mastering the excitonic interactions at the nanoscale are essential. In this Perspective, we highlight and critically consider the excitonic interactions in the organic−inorganic nanocomposites to achieve highly efficient exciton transfer through rational design of the nanocomposites. The use of strong excitonic interactions in optoelectronic devices can trigger efficiency breakthroughs in hybrid optoelectronics. B oth colloidal semiconductor nanocrystals (NCs) and π-conjugated semiconductor polymers (CPs) are attractive materials for a broad range of applications including bioimaging, 1,2 sensing, 3,4 electronics, 5,6 and photonics. 7,8 Using these emerging materials for energy-efficient lighting, display and photovoltaic technologies have gained escalating interest in the past 2 decades. 9−12 To this end, combining favorable optical properties of the colloidal semiconductor NCs and versatile physical properties of the conjugated polymers in hybrid platforms offers enabling opportunities for highperformance devices along with new functionalities. For this purpose, in the organic−inorganic composite systems, controlling the photophysical properties becomes crucial. These properties principally comprise excitons and excitonic processes, which include exciton formation, diffusion, transfer, and dissociation as well as radiative and nonradiative recombination of the excitons. These excitonic processes are schematically depicted in Figure 1.An exciton, which is a Coulombically bound electron−hole pair, is the primary form of the excited-state energy in the CPs and the NCs. An exciton can be created via either optical or electrical excitation (Figure 1a). Optical excitation occurs through absorption of a photon, while electrical excitation requires simultaneous injection of an electron and a hole. Within the lifetime of an exciton, it may radiatively or nonradiatively recombine (Figure 1b). Radiative recombination results in emission of a photon, whereas nonradiative recombination does not produce light but heat. Exciton diffusion (Figure 1c) is another process that is widely observed in the close-packed solid films of the CPs and the colloidal NCs. In the case of CPs, exciton diffusion/migration can happen either via exciton hopping within the delocalized excited-state landscape of CP 13 or via Forster resonance energy transfer (FRET) between different chromophoric units of the CP.14,15 In the colloidal NCs, exciton diffusion dominantly takes place through long-range nonradiative energy transfer because excitons are confined to the NCs. 16,17 The exciton diffusion length in ...

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“…Several chemistry groups have previously successfully attached various quantum dots to polymers having larger surface binding affinity than the ligands of these quantum dots and demonstrated hybrid structures of polymers and quantum dots. [7,8] For example, CdSe/ZnS quantum dots have been integrated with different polyfluorene (PF) derivatives. In this work, we used blue emitting carboxyl group functionalized polyfluorene derivative conjugated polymer, which serve as the donors in the hybrid structure, and core/shell CdSe/ZnS quantum dots, which serve as the acceptors.…”

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confidence: 99%

Non-radiative energy-transfer-driven quantum dot LEDs

Güzeltürk

Erdem

Ünal

et al. 2010

2010 IEEE Photinic Society's 23rd Annual Meeting

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Semiconductor nanocrystal quantum dots with their tunable optical properties, narrow photoluminescence, and high photostability have generated great interest in light-emitting device applications. [1,2] Such colloidal quantum dots that are directly electrically driven in light-emitting diode (LED) structures have been extensively studied in the last decade. However, these LEDs unfortunately suffer from the fundamental problem of poor charge injection into these nanocrystals, which have high potential barriers due to their ligands surrounding them. This problem has been investigated and attempted to be minimized through various optimization methods. [3,4] As a result, although today the device external quantum efficiencies can now reach ca 2.7 % [5], the main problem with charge injection still exists. On the other hand, conjugated conductive polymers are being used for organic based LEDs for several decades. These LEDs can reach higher quantum efficiencies over 20 % [6]. But these devices suffer in most of the cases from instabilities and degradation of the polymer active layers. To combine the advantages of each material system, hybrid organic-inorganic structures have also previously been investigated to obtain more ingenious devices. However, in all of these hybrid devices, the basic operation has mainly been based on the same mechanism of conventional charge injection into the nanocrystal active material.In this study, as a paradigm shift, we propose and demonstrate non-radiative energy-transfer-driven quantum dot LEDs that inject excitons into the active nanocrystal material, instead of injecting charges into them. For that we hybridize specially functionalized conjugated polymers to be attached to the colloidal quantum dots to drive them in the hybrid LED structure via Förster-type non-radiative energy transfer from the polymers to the dots when the LED is electrically biased. Under electrical injection, these quantum dots are therefore not directly electrically excited but through non-radiative resonance energy transfer from conjugated polymer donors that are electrically driven. This method can be an alternative route for quantum dot LEDs with possible prospects of higher external quantum efficiencies in the case of using properly chosen host polymer and transport layers. As a result highly efficient quantum dot based light emitting devices can be implemented using non-radiative energy transfer. To make a proof-of-concept demonstration, we utilize a simple device architecture that consists of glass/transparent oxide (ITO) /active layer /aluminum top contact, where the active layer is the hybrid composite of CdSe/ZnS QDs integrated with polyfluorene (PF) derivatives. In operation, PF is electrically driven, which transfers its excitons to QDs and these excited QDs in turn luminescence. Here we present electroluminescence from quantum dots via non-radiative energy transfer when the LED is electrically driven, along with a systematic study of optical characterizations that showed the strong evidence for ene...

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Characterization of Quantum Dot/Conducting Polymer Hybrid Films and Their Application to Light‐Emitting Diodes

Cited by 91 publications

References 27 publications

Fabrication of high efficient organic/CdSe quantum dots hybrid OLEDs by spin-coating method

Fabrication of high efficient organic/CdSe quantum dots hybrid OLEDs by spin-coating method

Organic–Inorganic Composites of Semiconductor Nanocrystals for Efficient Excitonics

Non-radiative energy-transfer-driven quantum dot LEDs

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