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We present a quantitative analysis of the loss of electroluminescence in light-emitting diodes (LEDs) based on poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) due to the combination of non-radiative trap-assisted recombination and exciton quenching at the metallic cathode. It is demonstrated that for an MEH-PPV LED the biggest efficiency loss, up to 45%, arises from extrinsic non-radiative recombination via electron traps. The loss caused by exciton quenching at the cathode proves only to be significant for devices thinner than 100 nm. Removal of electron traps by purification is expected to enhance the efficiency of polymer LEDs by more than a factor of two. (C) 2012 Elsevier B.V. All rights reserved.

Colour tuning of white polymer light emitting diode (LED) light sources can be attained by various methods at various stages in the production process of the lamps and/or by the design of the active material incorporated in the LEDs. In this contribution we will describe the methods and discuss the physical background of colour tuning. Furthermore, the material design has led to polymers which are more stable during electrical stress, so that colour shift during lifetime can be excluded for white polymer LEDs. © 2010 Elsevier B.V.

We report the self-aligned passivation of a current distribution grid for an organic light emitting diode (OLED) anode using a pulsed Joule heating method to align the passivation layer accurately on the metal grid. This method involves passing an electric current through the grid to cure a polymer dielectric. Uncured polymer is then rinsed away, leaving a patterned dielectric layer that conforms to the shape of the grid lines. To enhance the accuracy of the alignment, heat conduction into the substrate and the transparent electrode is limited by using short current pulses instead of a constant current. Excellent alignment accuracy of the dielectric layer on printed metal grid lines has been achieved, with a typical 4-μm dielectric overhang. In addition to good accuracy, pulsed Joule heating significantly cuts down process time and energy consumption compared to heating with a constant current. The feasibility of using a printed current distribution grid and Joule heating was demonstrated in an OLED device. cop. 2015 Author(s).

We report the self-aligned passivation of a current distribution grid for an organic light emitting diode (OLED) anode using a pulsed Joule heating method to align the passivation layer accurately on the metal grid. This method involves passing an electric current through the grid to cure a polymer dielectric. Uncured polymer is then rinsed away, leaving a patterned dielectric layer that conforms to the shape of the grid lines. To enhance the accuracy of the alignment, heat conduction into the substrate and the transparent electrode is limited by using short current pulses instead of a constant current. Excellent alignment accuracy of the dielectric layer on printed metal grid lines has been achieved, with a typical 4-μm dielectric overhang. In addition to good accuracy, pulsed Joule heating significantly cuts down process time and energy consumption compared to heating with a constant current. The feasibility of using a printed current distribution grid and Joule heating was demonstrated in an OLED device. cop. 2015 Author(s).

In this paper, we present some of the technology challenges and process temperature trade-offs when realizing AM OLED displays on thin flexible plastic films that can be mechanically bent to a roll radius of ∼1 cm. We furthermore present complementary approaches to realize low-power, high resolution OLED displays using self-aligned IGZO TFT architecture; a novel driving method using a compact 2T-1C pixel engine. cop. 2014 JSAP.

The efficiency of small-molecule OLED devices increased substantially in recent years, creating opportunities for power-efficient displays, as only light is generated proportional to the subpixel intensity. However, current active matrix OLED (AMOLED) displays on foil do not validate this power-efficient advantage, as too much power is lost in the AM backplane. AMOLED displays use the analog voltage on the gate of a drive transistor (e.g. M1 in Fig. 30.2.1) to control the pixel current and hence the pixel brightness. Accurate and uniform pixel currents can only be obtained when transistor M1 is driven is saturation. In highresolution technologies on foil, transistor parameters W, L and the mobility μ are limited by technology, imposing a minimal V GS-VT to obtain sufficient current, i.e. V GS-VT > 4V for a-IGZO on foil [1]. Subsequently, to obtain saturation, VDS > 4V, which translates in a static backplane power loss surpassing the OLED power consumption (see red stars in Fig 30.2.1). However, when the OLED pixel impedance around a specific reference current can be matched along a display column line, the accurate pixel current control can be imposed by current DACs implemented in external silicon display column drivers. In this work, we operate M1 as a switch and pixel intensity variations are obtained using Pulse Width Modulation (PWM) of a predefined pixel current, i.e. 2μA/pixel [80*80μm2] (which corresponds in our OLED technology to a light output of 2000Cd/m2). When, in a future implementation the external DACs are calibrated at 0.2μA/pixel, the full brightness would correspond to the typical display brightness of a portable PC, i.e. 200Cd/m2. This concept enables us to reduce the display power voltage at full brightness from 8.2V in a classical AMOLED display on foil configuration to 5V (measured) and for future implementations even down to 4V (see Fig. 30.2.1). As the OLED current load remains equal, a corresponding static power reduction of the display (and increased battery lifetime) is obtained. Digital driving methods of AMOLED displays have been shown before. However, ΔΣ techniques [2] still integrate charge packets on the gate of M1 and hence do not solve the power issue on foil. Other PWM techniques [3] activate only a single active line in the linedriver yielding difficulties to obtain color depths above 6 bits. When multiple independent linedrivers are implemented and their output is multiplexed to alternately drive a single select line, a higher color depth can be obtained [4]. This leads however to a bulky linedriver, which is hard to get within an e.g. 80μm pitch. The design and implementation of a compact integrated linedriver on foil enabling multiple alternating active signals through a single shift register is demonstrated here. © 2014 IEEE.

We present a QQVGA (160times120 with 3 sub-pixel) top-emitting AMOLED display with 85ppi resolution using a self-aligned (SA) IGZO TFT backplane on polyimide-foil. The back plane process flow is based on a 5 layer photolithography process. The aperture ratio of the top-emitting OLEDs is approx. 25%. For operation at 6 V supply voltage (VDD), the brightness of the display exceeds 150cd/m2. On the same substrate a 160 stage gate-driver was measured at FHD rate. cop. 2014 Society for Information Display.

We present a QQVGA (160times120 with 3 sub-pixel) top-emitting AMOLED display with 85ppi resolution using a self-aligned (SA) IGZO TFT backplane on polyimide-foil. The back plane process flow is based on a 5 layer photolithography process. The aperture ratio of the top-emitting OLEDs is approx. 25%. For operation at 6 V supply voltage (VDD), the brightness of the display exceeds 150cd/m2. On the same substrate a 160 stage gate-driver was measured at FHD rate. cop. 2014 Society for Information Display.

In this paper, we present some of the technology challenges and process temperature trade-offs when realizing AM OLED displays on thin flexible plastic films that can be mechanically bent to a roll radius of ∼1 cm. We furthermore present complementary approaches to realize low-power, high resolution OLED displays using self-aligned IGZO TFT architecture; a novel driving method using a compact 2T-1C pixel engine. cop. 2014 JSAP.

In applications such as organic light emitting diodes (OLEDs) or photovoltaic cells a homogenous voltage distribution in the large anode layer needs to be ensured by including a metal grid with a transparent conductor layer. To ensure sufficient conductivity, relatively thick metal lines are used, which increases the risk of electrical shorts between the anode and the cathode. For this reason an insulating layer is needed on top of the metal lines. The thick metal lines limit the choice of deposition method, since some methods such as spin coating require smooth surfaces and cannot be used for applying the insulator. Here, a spray coating process has been studied as a potential alternative deposition method to create thin resistive layers on rough surfaces. Spray coating and Joule heating has been used for the alignment of insulator films on printed metal lines. It was demonstrated that spray coating can be used to cover the printed metal lines which have high peaks on them. The spray coating forms electrically insulating layers even though the film thickness is less than the height of the peaks. The leakage current through the dielectric was on the order of 10-6 A/cm2.

The efficiency of small-molecule OLED devices increased substantially in recent years, creating opportunities for power-efficient displays, as only light is generated proportional to the subpixel intensity. However, current active matrix OLED (AMOLED) displays on foil do not validate this power-efficient advantage, as too much power is lost in the AM backplane. AMOLED displays use the analog voltage on the gate of a drive transistor (e.g. M1 in Fig. 30.2.1) to control the pixel current and hence the pixel brightness. Accurate and uniform pixel currents can only be obtained when transistor M1 is driven is saturation. In highresolution technologies on foil, transistor parameters W, L and the mobility μ are limited by technology, imposing a minimal V GS-VT to obtain sufficient current, i.e. V GS-VT > 4V for a-IGZO on foil [1]. Subsequently, to obtain saturation, VDS > 4V, which translates in a static backplane power loss surpassing the OLED power consumption (see red stars in Fig 30.2.1). However, when the OLED pixel impedance around a specific reference current can be matched along a display column line, the accurate pixel current control can be imposed by current DACs implemented in external silicon display column drivers. In this work, we operate M1 as a switch and pixel intensity variations are obtained using Pulse Width Modulation (PWM) of a predefined pixel current, i.e. 2μA/pixel [80*80μm2] (which corresponds in our OLED technology to a light output of 2000Cd/m2). When, in a future implementation the external DACs are calibrated at 0.2μA/pixel, the full brightness would correspond to the typical display brightness of a portable PC, i.e. 200Cd/m2. This concept enables us to reduce the display power voltage at full brightness from 8.2V in a classical AMOLED display on foil configuration to 5V (measured) and for future implementations even down to 4V (see Fig. 30.2.1). As the OLED current load remains equal, a corresponding static power reduction of the display (and increased battery lifetime) is obtained. Digital driving methods of AMOLED displays have been shown before. However, ΔΣ techniques [2] still integrate charge packets on the gate of M1 and hence do not solve the power issue on foil. Other PWM techniques [3] activate only a single active line in the linedriver yielding difficulties to obtain color depths above 6 bits. When multiple independent linedrivers are implemented and their output is multiplexed to alternately drive a single select line, a higher color depth can be obtained [4]. This leads however to a bulky linedriver, which is hard to get within an e.g. 80μm pitch. The design and implementation of a compact integrated linedriver on foil enabling multiple alternating active signals through a single shift register is demonstrated here. © 2014 IEEE.

In applications such as organic light emitting diodes (OLEDs) or photovoltaic cells a homogenous voltage distribution in the large anode layer needs to be ensured by including a metal grid with a transparent conductor layer. To ensure sufficient conductivity, relatively thick metal lines are used, which increases the risk of electrical shorts between the anode and the cathode. For this reason an insulating layer is needed on top of the metal lines. The thick metal lines limit the choice of deposition method, since some methods such as spin coating require smooth surfaces and cannot be used for applying the insulator. Here, a spray coating process has been studied as a potential alternative deposition method to create thin resistive layers on rough surfaces. Spray coating and Joule heating has been used for the alignment of insulator films on printed metal lines. It was demonstrated that spray coating can be used to cover the printed metal lines which have high peaks on them. The spray coating forms electrically insulating layers even though the film thickness is less than the height of the peaks. The leakage current through the dielectric was on the order of 10-6 A/cm2. acceptedVersion

Pinholes in the emitting layer of an organic light emitting diode (OLED), e.g. induced by particle contamination or processing flaws, lead to direct contact between the hole-injection layer (HIL) and the cathode. The resulting short circuits give rise to catastrophic device failure. We demonstrate that these short circuits can be effectively prevented by an oxidative treatment of the HIL with aqueous sodium hypochlorite (NaClO(aq), bleach), which locally lowers the conductivity of the HIL (i.e. poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)) by more than eight orders of magnitude while leaving the emitting layer virtually unaffected. The oxidizer treatment is evidenced by an order of magnitude reduction in leakage current and strong reduction in the number of bright spots in the emitting area, without affecting the device lifetime. Diode behavior is even recovered in deliberately flawed devices containing 80 μm sized defects. © 2014 Elsevier B.V. All rights reserved.

Pinholes in the emitting layer of an organic light emitting diode (OLED), e.g. induced by particle contamination or processing flaws, lead to direct contact between the hole-injection layer (HIL) and the cathode. The resulting short circuits give rise to catastrophic device failure. We demonstrate that these short circuits can be effectively prevented by an oxidative treatment of the HIL with aqueous sodium hypochlorite (NaClO(aq), bleach), which locally lowers the conductivity of the HIL (i.e. poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)) by more than eight orders of magnitude while leaving the emitting layer virtually unaffected. The oxidizer treatment is evidenced by an order of magnitude reduction in leakage current and strong reduction in the number of bright spots in the emitting area, without affecting the device lifetime. Diode behavior is even recovered in deliberately flawed devices containing 80 μm sized defects. © 2014 Elsevier B.V. All rights reserved.

We have developed a full color flexible top-emission AMOLED display with 80 ppi resolution using In-Ga-Zn-O TFT backplane on PEN foil under the maximum process temperature of 150 oC. Notwithstanding the low processing temperature, the TFTs with SiOx passivation layer show high reliability with VTH shift of less than 0.2 V at 10,000 seconds under bias-stress of -10 V. cop. 2013 Society for Information Display.

The availability of a high performance thin-film barrier is the most critical challenge in upscaling and commercializing flexible OLED products. We report a flexible thin-film-barrier technology that meets lifetime specifications for OLED lighting, and demonstrate it in rollable QVGA a-IGZO AMOLED displays. Roll-to-roll manufacturing of this high performance barrier film will be presented. cop. 2013 Society for Information Display.

The availability of a high performance thin-film barrier is the most critical challenge in upscaling and commercializing flexible OLED products. We report a flexible thin-film-barrier technology that meets lifetime specifications for OLED lighting, and demonstrate it in rollable QVGA a-IGZO AMOLED displays. Roll-to-roll manufacturing of this high performance barrier film will be presented. cop. 2013 Society for Information Display.

We present a quantitative analysis of the loss of electroluminescence in light-emitting diodes (LEDs) based on poly[2-methoxy-5-(2′-ethylhexyloxy)- p-phenylenevinylene] (MEH-PPV) due to the combination of non-radiative trap-assisted recombination and exciton quenching at the metallic cathode. It is demonstrated that for an MEH-PPV LED the biggest efficiency loss, up to 45%, arises from extrinsic non-radiative recombination via electron traps. The loss caused by exciton quenching at the cathode proves only to be significant for devices thinner than 100 nm. Removal of electron traps by purification is expected to enhance the efficiency of polymer LEDs by more than a factor of two. © 2012 Elsevier B.V. All rights reserved.

Passive or active matrix driving schemes in large displays are prone to high power consumption and cost, respectively. For signage applications such as large out-door displays with low refresh rates there is as yet no technological solution. Here the MEMOLED solution, an organic light-emitting diode with an integrated ferroelectric memory, is presented. Programmability of the integrated memory allows active addressing of the OLED in a passive matrix geometry. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The charge transport in blue light-emitting polyspirobifluorene is investigated by both steady-state current-voltage measurements and transient electroluminescence. Both measurement techniques yield consistent results and show that the hole transport is space-charge limited. The electron current is found to be governed by a high intrinsic mobility in combination with electron traps. Numerical simulations on light-emitting diodes reveal a shift in the recombination zone from the cathode to the anode with increasing bias. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Passive or active matrix driving schemes in large displays are prone to high power consumption and cost, respectively. For signage applications such as large out-door displays with low refresh rates there is as yet no technological solution. Here the MEMOLED solution, an organic light-emitting diode with an integrated ferroelectric memory, is presented. Programmability of the integrated memory allows active addressing of the OLED in a passive matrix geometry. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

N-type doping of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) with decamethylcobaltocene (DMC) strongly improves the electron transport due to filling of the electron traps. Unexpectedly, the n-type doping simultaneously suppresses the hole transport in MEH-PPV. We demonstrate that this strong reduction of the hole transport originates from unionized DMC molecules that act as hole traps. This hole trapping effect explains why the current of a DMC-doped MEH-PPV polymer light-emitting diode is orders of magnitude lower than that of the undoped device. © 2011 Wiley Periodicals, Inc.

N-type doping of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) with decamethylcobaltocene (DMC) strongly improves the electron transport due to filling of the electron traps. Unexpectedly, the n-type doping simultaneously suppresses the hole transport in MEH-PPV. We demonstrate that this strong reduction of the hole transport originates from unionized DMC molecules that act as hole traps. This hole trapping effect explains why the current of a DMC-doped MEH-PPV polymer light-emitting diode is orders of magnitude lower than that of the undoped device. © 2011 Wiley Periodicals, Inc.

The charge transport in blue light-emitting polyspirobifluorene is investigated by both steady-state current-voltage measurements and transient electroluminescence. Both measurement techniques yield consistent results and show that the hole transport is space-charge limited. The electron current is found to be governed by a high intrinsic mobility in combination with electron traps. Numerical simulations on light-emitting diodes reveal a shift in the recombination zone from the cathode to the anode with increasing bias. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The roll-to-roll manufacturing process is believed to significantly reduce the cost-price of flexible electronics. Inkjet printing of organic-based inks is a major research topic for flexible electronic applications because of its advantage of non- contact deposition and the ease for patterning for various industrial processes. We herein present a study on inkjet printing of homogeneous layers of Orgacon™ (Agfa-Gevaert, Belgium). Orgacon™ is a water-based dispersion of poly (3,4- ethylenedioxythiophene): poly(styrenesulphonic acid (PEDOT:PSS). This printed layer can be used as a transparent electrode for the Organic Light Emitting Diodes (OLEDs) and for Organic Photovoltaic (OPV). For OLED lighting applications, uniform light emission of large areas is required; the main challenge of using inkjet technology is the deposition of highly homogenous layers onto flexible non-porous foil substrates. In this contribution, some of the fundamental aspects of inkjet ink and substrate interaction, and the resulting layer homogeneity of the active layer in relation to OLED and OPV-device performance are investigated. Combining both theoretical and experimental approaches, we studied the inkjet ink rheology and homogenous layer formation on a moisture barrier. We have enabled to deposit homogenous PEDOT and LEP using commercially available inkjet heads. Furthermore, we would like to demonstrate the ability of using inkjet printing for fabrication of 1 "by 1 "OLED devices, with Agfa high conductive PEDOT.PSS and Merck light emitting polymers dissolved in solution. The inkjet ink properties and the substrate pretreatment have been optimized in order to ensure a stable and robust printing and drying process. Moreover, inkjet printed OLEDs will be demonstrated and the resulting light emission uniformity, device performance and reliability on flexible substrates will be discussed.

The roll-to-roll manufacturing process is believed to significantly reduce the cost-price of flexible electronics. Inkjet printing of organic-based inks is a major research topic for flexible electronic applications because of its advantage of non- contact deposition and the ease for patterning for various industrial processes. We herein present a study on inkjet printing of homogeneous layers of Orgacon™ (Agfa-Gevaert, Belgium). Orgacon™ is a water-based dispersion of poly (3,4- ethylenedioxythiophene): poly(styrenesulphonic acid (PEDOT:PSS). This printed layer can be used as a transparent electrode for the Organic Light Emitting Diodes (OLEDs) and for Organic Photovoltaic (OPV). For OLED lighting applications, uniform light emission of large areas is required; the main challenge of using inkjet technology is the deposition of highly homogenous layers onto flexible non-porous foil substrates. In this contribution, some of the fundamental aspects of inkjet ink and substrate interaction, and the resulting layer homogeneity of the active layer in relation to OLED and OPV-device performance are investigated. Combining both theoretical and experimental approaches, we studied the inkjet ink rheology and homogenous layer formation on a moisture barrier. We have enabled to deposit homogenous PEDOT and LEP using commercially available inkjet heads. Furthermore, we would like to demonstrate the ability of using inkjet printing for fabrication of 1 "by 1 "OLED devices, with Agfa high conductive PEDOT.PSS and Merck light emitting polymers dissolved in solution. The inkjet ink properties and the substrate pretreatment have been optimized in order to ensure a stable and robust printing and drying process. Moreover, inkjet printed OLEDs will be demonstrated and the resulting light emission uniformity, device performance and reliability on flexible substrates will be discussed.

A femtosecond laser has been successfully utilized for patterning thin Flexible Organic Light Emitting Diode (FOLED) structures of individual layer thickness around 100nm. The authors report in this paper a step-like ablation behavior at the layer interfaces which accounts for a local removal of entire layers. Various surface analyzing techniques are used to investigate the morphologies and chemical compositions within and in the vicinity of the ablation areas. This study opens a new avenue in selectively ablating different layers from a multilayer stack on flexible substrates using fs lasers allowing post deposition structuring of large area flexible organic electronic devices. © 2010 Optical Society of America.

Colour tuning of white polymer light emitting diode (LED) light sources can be attained by various methods at various stages in the production process of the lamps and/or by the design of the active material incorporated in the LEDs. In this contribution we will describe the methods and discuss the physical background of colour tuning. Furthermore, the material design has led to polymers which are more stable during electrical stress, so that colour shift during lifetime can be excluded for white polymer LEDs. © 2010 Elsevier B.V.

A femtosecond laser has been successfully utilized for patterning thin Flexible Organic Light Emitting Diode (FOLED) structures of individual layer thickness around 100nm. The authors report in this paper a step-like ablation behavior at the layer interfaces which accounts for a local removal of entire layers. Various surface analyzing techniques are used to investigate the morphologies and chemical compositions within and in the vicinity of the ablation areas. This study opens a new avenue in selectively ablating different layers from a multilayer stack on flexible substrates using fs lasers allowing post deposition structuring of large area flexible organic electronic devices. (C)2010 Optical Society of America