Implementation of anti-reflection coating to enhance light out-coupling in organic light-emitting devices

Saxena, Kanchan; Mehta, Dalip Singh; Kumar, Virendra; Srivastava, Ritu; Chauhan, Gayatri; Kamalasanan, M. N.

doi:10.1016/j.jlumin.2007.09.028

Cited by 35 publications

(13 citation statements)

References 27 publications

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“…An index-matching layer has also been used for top emitting OLED (Hung et al 2001). To extract the trapped light, Saxena et al (2008) used simple AR coating technique and demonstrated pronounced enhancement in light out-coupling of conventional OLED. Single-layer MgF 2 was coated on backside of glass substrate of conventional OLED with thickness of λ/4.…”

Section: Improving Out Coupling Efficiencymentioning

confidence: 99%

Organic Light Emitting Diodes for White Light Emission

Srivastava¹,

Kamalasanan²,

Chauhan³

et al. 2010

Organic Light Emitting Diode

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National Physical Laboratory New Delhi has taken up a program for developing WOLEDs for general lighting applications. In this effort a 1"x1" proto type of a multilayer phosphorescent efficient WOLED has been demonstrated (Fig.2). In this review, we like to highlight on the development of white organic LEDs for general lighting. 2. Basic OLED Structure and Operation principles White organic light emitting diodes are thin-film multilayer devices in which active charge transport and light emitting materials are sandwiched between two thin film electrodes, and at least one of the two electrodes must be transparent to light. Generally high work function (∼4.8 eV), low sheet resistant (20 /□) and optically transparent indium tin oxide (ITO) is used as an anode, while the cathode is a low work function metal such as Ca, Mg, Al or their alloys Mg:Ag, Li:Al. An organic layer with good electron transport and hole blocking properties is typically used between the cathode and the emissive layer. The device structure of an OLED is given in Fig. 3. When an electric field is applied across the electrodes, electrons and holes are injected into states of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), respectively and transported through the organic layer. Inside the semiconductor electrons and holes recombine to form excited state of the molecule. Light emission from the organic material occurs when the molecule relaxes from the excited state to the ground state. Highly efficient OLEDs which are being developed at present, contains many layers with different functionality like hole injection layer(HIL), hole transport layer (HTL),electron blocking layer(EBL), emissive layer(EML), hole blocking layer(HBL), electron transport layer(ETL) and electron injection layer(EIL) etc apart from electrodes. A schematic diagram of multilayer structure is shown in Fig. 4.

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Section: Improving Out Coupling Efficiencymentioning

confidence: 99%

Organic Light Emitting Diodes for White Light Emission

Srivastava¹,

Kamalasanan²,

Chauhan³

et al. 2010

Organic Light Emitting Diode

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“…Many different approaches had been done with the aim of optimizing the light outcoupling for OLEDs, including low-index grids [6,7], periodic corrugated structure [8], Bragg mirrors [9,10], buckling patterns [11], photonic crystals [12,13], antireflection coatings [14], and monolayer of SiO 2 microparticles [15]. Those methods focused on changing the contact surface of glass substrate with organic device, which were also complicated to achieve them.…”

Section: Introductionmentioning

confidence: 99%

Improving Light Outcoupling Efficiency for OLEDs with Microlens Array Fabricated on Transparent Substrate

Wang

2014

Journal of Nanomaterials

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Low light outcoupling efficiency restricts the wide application of organic light-emitting diodes in solid state light market although the internal quantum efficiency of the device could reach near to 100%. In order to improve the output efficiency, different kinds of microlens array on the substrate emission surface were designed and simulated using light tracing method. Simulation results indicate that the microlens array on the substrate could efficiently improve the light output efficiency and an enhancement of 1.8 could be obtained with optimized microlens structure design. The microlens array with semicircle shape using polymer material was fabricated on glass substrate by a facile approach. Finally, the organic device with microlens array substrate was manufactured and the light output of the device with surface microlens structure could increase to 1.64 times comparing with the device without microlens.

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“…In recent years, implementing an anti-reflection (AR) layer to solve the trade-off problem had been reported [22]. In this method, a single MgF 2 layer was deposited on the glass substrate with a thickness of λ/4 which destructed the interference of reflected light from the substrate.…”

Section: Introductionmentioning

confidence: 99%

Efficiency enhancement of flexible organic light-emitting devices by using antireflection nanopillars

Liu

et al. 2011

Opt. Express

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We present an antireflection structure consisted of irregular nanopillars to increase light extraction efficiency of flexible organic light-emitting devices. The nanopillars were made by imprinting the anodized aluminum oxide on polycarbonate substrates. The thermal viscosity effect formed the nanopillars with tapered shapes. Such nanopillars show excellent antireflection properties for a wide range of incident angles and wavelengths. The normal transmittance was improved from 85.5% to 95.9% for 150-nm-height nanopillars. The transmittance was greatly improved from 52.8% to 89.1% at 60° incident angle. With this antireflection structure, the device efficiency was improved 69% as compared to devices with flat substrates. Due to wide-angle antireflection, the image contrast ratio was also significantly improved.

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Implementation of anti-reflection coating to enhance light out-coupling in organic light-emitting devices

Cited by 35 publications

References 27 publications

Organic Light Emitting Diodes for White Light Emission

Organic Light Emitting Diodes for White Light Emission

Improving Light Outcoupling Efficiency for OLEDs with Microlens Array Fabricated on Transparent Substrate

Efficiency enhancement of flexible organic light-emitting devices by using antireflection nanopillars

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