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Henk J Bolink - One of the best experts on this subject based on the ideXlab platform.

  • light emitting Electrochemical Cells and solution processed organic light emitting diodes using small molecule organic thermally activated delayed fluorescence emitters
    Chemistry of Materials, 2015
    Co-Authors: Michael Y Wong, Antonio Pertegas, Henk J Bolink, Gordon J Hedley, Lisa S Kolln, Ifor D W Samuel, Eli Zysmancolman
    Abstract:

    Two novel charged organic thermally activated delayed fluorescence (TADF) emitters, 1 and 2, have been synthesized. Their TADF behavior is well-supported by the multiexponential decay of their emission (nanosecond and microsecond components) and the oxygen dependence of the photoluminescence quantum yields. Spin-coated electroluminescent devices have been fabricated to make light-emitting Electrochemical Cells (LEECs) and organic light-emitting diodes (OLEDs). The first example of a non-doped charged small organic molecule LEEC is reported and exhibited an external quantum efficiency (EQE) of 0.39% using 2. With a multilayer architecture, a solution-processed OLED device using neat 2 as the emitting layer gave an EQE of 5.1%, the highest reported to date for a nondoped solution-processed small molecule organic TADF OLED. These promising results open up a new area in light-emitting materials for the development of low-cost TADF LEECs.

  • light emitting Electrochemical Cells using cyanine dyes as the active components
    Journal of the American Chemical Society, 2013
    Co-Authors: Antonio Pertegas, Daniel Tordera, Juan Jose Serranoperez, Enrique Orti, Henk J Bolink
    Abstract:

    Light-emitting Electrochemical Cells (LECs) based on cyanine molecules were prepared. High photoluminescence quantum yields were obtained for host–guest films using two cyanine dyes, reaching 27%. Sandwiching these films in between two electrodes allows for very stable near-infrared emission with a maximum radiant flux of 1.7 W m–2 at an external quantum efficiency of 0.44%.

  • a deep blue emitting charged bis cyclometallated iridium iii complex for light emitting Electrochemical Cells
    Journal of Materials Chemistry C, 2013
    Co-Authors: Daniel Tordera, Enrique Orti, Henk J Bolink, Sebastian Meier, Wiebke Sarfert, Jose M Junquerahernandez, Manuel Delgado, Florian Kessler, Rosario Scopelliti
    Abstract:

    We report here a new cationic bis-cyclometallated iridium(III) complex, 1, with deep-blue emission at 440 nm and its use in Light-emitting Electrochemical Cells (LECs). The design is based on the 2′,6′-difluoro-2,3′-bipyridine skeleton as the cyclometallating ligand and a bis-imidazolium carbene-type ancillary ligand. Furthermore, bulky tert-butyl substituents are used to limit the intermolecular interactions. LECs have been driven both at constant voltage (6 V) and constant current (2.5 mA cm−2). The performances are significantly improved with the latter method, resulting overall in one of the best reported greenish-blue LECs having fast response (17 s), light intensity over 100 cd m−2 and a reasonable efficiency of almost 5 cd A−1.

  • luminescent ionic transition metal complexes for light emitting Electrochemical Cells
    ChemInform, 2012
    Co-Authors: Ruben D Costa, Enrique Orti, Henk J Bolink, Filippo Monti, Gianluca Accorsi, Nicola Armaroli
    Abstract:

    Higher efficiency in the end-use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid-state electroluminescent materials and belong to the general area of solid-state lighting (SSL). The two main technologies being developed in SSL are light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs), but in recent years, light-emitting Electrochemical Cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition-metal complexes (iTMCs). Cyclometalated complexes of IrIII are by far the most utilized class of iTMCs in LECs. Herein, we show how these complexes can be prepared and discuss their unique electronic, photophysical, and photochemical properties. Finally, the progress in the performance of iTMCs based LECs, in terms of turn-on time, stability, efficiency, and color is presented.

  • stable and efficient solid state light emitting Electrochemical Cells based on a series of hydrophobic iridium complexes
    Advanced Energy Materials, 2011
    Co-Authors: Ruben D Costa, Antonio Pertegas, Daniel Tordera, Enrique Orti, Henk J Bolink, Stefan Graber, Catherine E Housecroft, Ludmila Sachno, Markus Neuburger
    Abstract:

    Light-emitting Electrochemical Cells (LECs) based on ionic transition-metal complexes (iTMCs) exhibiting high efficiency, short turn-on time, and long stability have recently been presented. Furthermore, LECs emitting in the full range of the visible spectrum including white light have been reported. However, all these achievements were obtained individually, not simultaneously, using in each case a different iTMC. In this work, device stability is maintained by employing intrinsically stable ionic iridium complexes, while increasing the complex and the device quantum yields for exciton-to-photon conversion. This is done by sequentially modifying the archetype ionic iridium complex [Ir(ppy)(2)(bpy)][PF(6)], where Hppy is 2-phenylpyridine and bpy is 2,2`-bipyridine, with methyl and phenyl groups on the bpy ligand. A full photophysical and theoretical description of a series of four complexes, including the archetype as a reference, is presented and their performance in LECs is characterized. Upon selecting suitable substituents, a twofold increase is obtained in the photoluminescence quantum yield in a solid film. This is reflected in a significant increase in the efficiency over time curve for LECs using this complex.

Youngson Choe - One of the best experts on this subject based on the ideXlab platform.

  • synthesis of heteroleptic iridium complexes with sterically hindered methyl groups on pyrazole ligands for efficient yellow and green light emitting Electrochemical Cells
    Dyes and Pigments, 2016
    Co-Authors: Chozhidakath Damodharan Sunesh, Madayanad Suresh Subeesh, Kanagaraj Shanmugasundaram, Ramesh Kumar Chitumalla, Joonkyung Jang, Youngson Choe
    Abstract:

    Abstract We report the synthesis of four cationic iridium complexes, [Ir(ppy) 2 (mepzpy)]PF 6 ( 1a ), [Ir(dfppy) 2 (mepzpy)]PF 6 ( 1b ), [Ir(ppy) 2 (dmpzpy)]PF 6 ( 2a ), and [Ir(dfppy) 2 (dmpzpy)]PF 6 ( 2b ), containing the methyl-substituted pyrazole-based ancillary ligand and the phenylpyridine-based cyclometalating ligands. UV–visible, photoluminescence (PL), and voltammetric measurements were made to study the photophysical and Electrochemical properties of complexes 1a – 2b . Light-emitting Electrochemical Cells (LECs) were fabricated, which showed yellow emission for complexes 1a and 2a and green emission for complexes 1b and 2b . The LEC incorporating 2b exhibited a high luminance of 658 cd m −2 and a current efficiency of 0.34 cd A −1 . The higher luminance and efficiency of the device based on 2b were due to the smooth surface morphology and the presence of sterically hindered dimethyl groups on the ancillary ligand (dmpzpy), which causes a more balanced charge carrier injection and recombination.

  • utilization of a phenanthroimidazole based fluorophore in light emitting Electrochemical Cells
    Journal of Materials Chemistry C, 2015
    Co-Authors: Madayanad Suresh Subeesh, Kanagaraj Shanmugasundaram, Chozhidakath Damodharan Sunesh, Yong Sun Won, Youngson Choe
    Abstract:

    An easily accessible, highly soluble, small-molecule phenanthroimidazole derivative has been synthesized and characterized. The synthesized compound shows strong luminescence in solution and exhibits good thermal stability. Single crystal X-ray crystallography studies were carried out. Correlations between the X-ray structures, photophysical properties and the performance in light-emitting Electrochemical Cells (LECs) are described. A yellowish green emission was achieved by using the target compound in a LEC device configuration. The constructed prototype device performance was promising with a maximum brightness of 125 cd m−2. The results suggest that the phenanthroimidazole derivative can function as an active material in LEC devices.

  • highly luminescent yellow and yellowish green light emitting Electrochemical Cells based on cationic iridium complexes with phenanthroline based ancillary ligands
    Optical Materials, 2013
    Co-Authors: Chozhidakath Damodharan Sunesh, Midhun Chandran, George Mathai, Youngson Choe
    Abstract:

    Abstract Highly luminescent light-emitting Electrochemical Cells (LECs) based on cationic iridium complexes [Ir(ppz) 2 (dpphen)]PF 6 (1) and [Ir(ppz) 2 (tmphen)]PF 6 (2) (ppz is 1-phenylpyrazole, dpphen is 4,7-diphenyl-1,10-phenanthroline and tmphen is 3,4,7,8-tetramethyl-1,10-phenanthroline) with phenanthroline based ancillary ligands were fabricated using air stable electrodes and their electroluminescent properties were investigated. LECs based on complex 1 emitted yellow electroluminescence ( λ max 574 nm) with Commission Internationale de L’Eclairage (CIE) coordinates of (0.49, 0.50) while the complex 2 gave yellowish-green electroluminescence ( λ max 537 nm) with CIE coordinates of (0.35, 0.58). The work done here reveals that the alkyl substituted phenanthroline ancillary ligand, tmphen shifts the light emission to the shorter wavelength region than the phenyl substituted dpphen ligand, resulting in the color tuning of the light-emitting devices. Density functional theory (DFT) calculations were performed to gain insight into the molecular surfaces of cationic iridium complexes and their Electrochemical behaviors. Single layer LECs based on these complexes exhibited a high luminescence of 5199 and 4751 cd/m 2 for complexes 1 and 2 respectively. The ionic liquid, 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF 6 ) was added to the light emitting layer and hence higher luminances were obtained than the pristine device.

  • effect of ionic liquids on the electroluminescence of yellowish green light emitting Electrochemical Cells using bis 2 2 4 difluorophenyl pyridine 4 7 diphenyl 1 10 phenanthroline iridium iii hexafluorophosphate
    Materials Chemistry and Physics, 2012
    Co-Authors: Chozhidakath Damodharan Sunesh, Midhun Chandran, Ok Sunseong, Danbi Moon, Youngson Choe
    Abstract:

    Abstract A cationic iridium complex [Ir(dfppy)2(dpphen)]PF6, where dfppy is 2-(2,4-difluorophenyl)pyridine, dpphen is 4,7-diphenyl-1,10-phenanthroline and PF6− is hexafluorophosphate, has been synthesized and its photophysical and Electrochemical properties were investigated. Light-emitting Electrochemical Cells (LECs) based on this complex were fabricated using air stable electrodes and emits yellowish-green light (533 nm) with Commission Internationale de L’Eclairage (CIE) coordinates of (0.35, 0.59) at 4 V. Effect of two different imidazolium based ionic liquids (ILs) viz, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) and 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF6) on the active layer has been studied and the luminance and the current density of the devices were found to be enhanced with increasing ionic conductivities.

Ruben D Costa - One of the best experts on this subject based on the ideXlab platform.

  • from white to red electric field dependent chromaticity of light emitting Electrochemical Cells based on archetypal porphyrins
    Advanced Functional Materials, 2016
    Co-Authors: Michael D Weber, Judith E Wittmann, Alexandra Burger, Osman Baris Malcioglu, Javier Segarramarti, Andreas Hirsch, Pedro B Coto, Michel Bockstedte, Ruben D Costa
    Abstract:

    The differences in the electroluminescence (EL) of red-emitting free-base (H2TPP) and Zn-metalated (ZnTPP) archetypal porphyrins are rationalized in light-emitting Electrochemical Cells by means of an electric-field dependent effect, leading to whitish and reddish devices, respectively. Although H2TPP shows superior Electrochemical and photophysical features compared to ZnTPP, devices prepared with ZnTPP surprisingly stand out with a deep-red EL similar to its photoluminescence (PL), while H2TPP devices feature unexpected whitish EL. Standard arguments such as degradation, device architecture, device mechanism, and changes in the nature of the emitting excited states are discarded. Based on Electrochemical impedance spectroscopy and first-principles electronic structure methods, we provide evidence that the EL originates from two H2TPP regioisomers, in which the inner ring H atoms are placed in collinear and vicinal configurations. The combination of their optical features provides an explanation for both the high- and low-energy EL features. Here, the emitting excited state nature is ascribed to the Q bands, since the Soret excited states remain high in energy. This contrasts to what is traditionally postulated in reports focused on H2TPP lighting devices. Hence, this work provides a new explanation for the nature of the high-energy EL band of H2TPP that might inspire future works focused on white-emitting molecular-based devices.

  • controlling the chromaticity of small molecule light emitting Electrochemical Cells based on tips pentacene
    Advanced Functional Materials, 2015
    Co-Authors: Michael D Weber, Matthias Adam, Rik R Tykwinski, Ruben D Costa
    Abstract:

    This work demonstrates a novel proof-of-concept to implement pentacene derivatives as emitters for the third generation of light-emitting Electrochemical Cells based on small-molecules (SM-LECs). Here, a straightforward procedure is shown to control the chromaticity of pentacene-based lighting devices by means of a photoinduced cycloaddition process of the 6,13-bis(triisopropylsilylethynyl) (TIPS)-pentacene that leads to the formation of anthracene-core dimeric species featuring a high-energy emission. Without using the procedure, SM-LECs featuring deep-red emission with Commission Internationale d'Eclairage (CIE) coordinates of x = 0.69/y = 0.31 and irradiance of 0.4 μW cm−2 are achieved. After a careful optimization of the cycloaddition process, warm white devices with CIE coordinates of x = 0.36/y = 0.38 and luminances of 10 cd m−2 are realized. Here, the mechanism of the device is explained as a host–guest system, in which the dimeric species acts as the high-energy band gap host and the low-energy bandgap TIPS-pentacene is the guest. To the best of the knowledge, this work shows the first warm white SM-LECs. Since this work is based on the archetypal TIPS-pentacene and the photoinduced cycloaddition process is well-knownfor any pentacenes, this proof-of-concept could open a new way to use these compounds for developing white lighting sources.

  • luminescent ionic transition metal complexes for light emitting Electrochemical Cells
    ChemInform, 2012
    Co-Authors: Ruben D Costa, Enrique Orti, Henk J Bolink, Filippo Monti, Gianluca Accorsi, Nicola Armaroli
    Abstract:

    Higher efficiency in the end-use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid-state electroluminescent materials and belong to the general area of solid-state lighting (SSL). The two main technologies being developed in SSL are light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs), but in recent years, light-emitting Electrochemical Cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition-metal complexes (iTMCs). Cyclometalated complexes of IrIII are by far the most utilized class of iTMCs in LECs. Herein, we show how these complexes can be prepared and discuss their unique electronic, photophysical, and photochemical properties. Finally, the progress in the performance of iTMCs based LECs, in terms of turn-on time, stability, efficiency, and color is presented.

  • stable and efficient solid state light emitting Electrochemical Cells based on a series of hydrophobic iridium complexes
    Advanced Energy Materials, 2011
    Co-Authors: Ruben D Costa, Antonio Pertegas, Daniel Tordera, Enrique Orti, Henk J Bolink, Stefan Graber, Catherine E Housecroft, Ludmila Sachno, Markus Neuburger
    Abstract:

    Light-emitting Electrochemical Cells (LECs) based on ionic transition-metal complexes (iTMCs) exhibiting high efficiency, short turn-on time, and long stability have recently been presented. Furthermore, LECs emitting in the full range of the visible spectrum including white light have been reported. However, all these achievements were obtained individually, not simultaneously, using in each case a different iTMC. In this work, device stability is maintained by employing intrinsically stable ionic iridium complexes, while increasing the complex and the device quantum yields for exciton-to-photon conversion. This is done by sequentially modifying the archetype ionic iridium complex [Ir(ppy)(2)(bpy)][PF(6)], where Hppy is 2-phenylpyridine and bpy is 2,2`-bipyridine, with methyl and phenyl groups on the bpy ligand. A full photophysical and theoretical description of a series of four complexes, including the archetype as a reference, is presented and their performance in LECs is characterized. Upon selecting suitable substituents, a twofold increase is obtained in the photoluminescence quantum yield in a solid film. This is reflected in a significant increase in the efficiency over time curve for LECs using this complex.

  • intramolecular pi stacking in a phenylpyrazole based iridium complex and its use in light emitting Electrochemical Cells
    Journal of the American Chemical Society, 2010
    Co-Authors: Ruben D Costa, Enrique Orti, Henk J Bolink, Stefan Graber, Catherine E Housecroft, Edwin C Constable
    Abstract:

    A novel iridium(III) complex, [Ir(dmppz)2pbpy][PF6] (Hdmppz = 3,5-dimethyl-1-phenylpyrazole and pbpy = 6-phenyl-(2,2′-bipyridine)), is reported. The complex shows an intramolecular face-to-face π-stacking between the phenyl ring of the dmppz ligand and the pendant phenyl of the pbpy ligand. This interaction provides a supramolecular cage formation that holds also in the excited states. Light-emitting Electrochemical Cells (LECs) using the novel complex show extraordinary lifetimes of ∼2000 h. The high stability is favored by the presence of pendant methyl groups on the dmppz ligands that hinder the entrance of water molecules rendering the degradation of the complex more difficult.

Jun Chen - One of the best experts on this subject based on the ideXlab platform.

  • the significance of supporting electrolyte on poly vinyl alcohol iron ii iron iii solid state electrolytes for wearable thermo Electrochemical Cells
    Electrochemistry Communications, 2021
    Co-Authors: Yuetong Zhou, Yuqing Liu, Mark A Buckingham, Shuai Zhang, Leigh Aldous, Stephen Beirne, Gordon G Wallace, Jun Chen
    Abstract:

    Abstract Thermo-Electrochemical Cells (known as thermoCells) can convert heat energy into electrical power through redox reactions driven by the presence of a temperature gradient. Low-grade heat from the human body can be harvested using thermoCells containing a suitable electrolyte, such as the iron(II)/iron(III) chloride redox couple housed in poly (vinyl alcohol) described here. However, conventionally the thermo-Electrochemical performance of gelled electrolytes is poor, due to slow ionic transport and high charge transfer resistance. In this report, hydrochloric acid has been found to synergistically decrease the charge transfer resistance of the redox reaction, whilst doubling the tensile properties of the gel housing. Moreover, individual thermoCells can be connected in parallel to enhance current output.

  • Potentially Wearable Thermo‐Electrochemical Cells for Body Heat Harvesting: From Mechanism, Materials, Strategies to Applications
    'Wiley', 2021
    Co-Authors: Yuqing Liu, Hongbo Wang, Peter C. Sherrell, Lili Liu, Yong Wang, Jun Chen
    Abstract:

    Abstract Wearable electronics are becoming one of the key technologies in health care applications including health monitoring, data acquisitions, and real‐time diagnosis. The commercialization of next‐generation devices has been stymied by the lack of ultrathin, flexible, and reliable power sources. Wearable thermo‐Electrochemical Cells (TECs), which can convert body heat to electricity via an Electrochemical process, are showing great promise as power sources for such wearable systems. TECs harvest orders of magnitude more voltage per temperature difference (Seebeck coefficient (1–34 mV K−1)) when compared to the more common thermoelectric generators (Seebeck coefficient ≈tens or hundreds of µV K−1). However, there still remain great challenges for TECs progressing towards wearable applications. This review summarizes the recent development of potentially wearable TECs with promise for body‐heat harvesting, with a specific focus on flexible electrode materials, solid‐state electrolytes, device fabrication, and strategies toward applications. It also clarifies the challenges and gives some future direction to enhance future investigations on high‐performance wearable TECs for practical and self‐powered wearable devices

  • proton intercalation de intercalation dynamics in vanadium oxides for aqueous aluminum Electrochemical Cells
    Angewandte Chemie, 2020
    Co-Authors: Qing Zhao, Jun Chen, Luojia Liu, Jiefu Yin, Jingxu Zheng, Duhan Zhang, Lynden A Archer
    Abstract:

    Understanding cation (H+ , Li+ , Na+ , Al3+ , etc.) intercalation/de-intercalation chemistry in transition metal compounds is crucial for the design of cathode materials in aqueous Electrochemical Cells. Here we report that orthorhombic vanadium oxides (V2 O5 ) supports highly reversible proton intercalation/de-intercalation reactions in aqueous media, enabling aluminum Electrochemical Cells with extended cycle life. Empirical analyses using vibrational and x-ray spectroscopy are complemented with theoretical analysis of the electrostatic potential to establish how and why protons intercalate in V2 O5 in aqueous media. We show further that cathode coatings composed of cation selective membranes provide a straightforward method for enhancing cathode reversibility by preventing anion cross-over in aqueous electrolytes. Our work sheds light on the design of cation transport requirements for high-energy reversible cathodes in aqueous Electrochemical Cells.

Yuqing Liu - One of the best experts on this subject based on the ideXlab platform.

  • the significance of supporting electrolyte on poly vinyl alcohol iron ii iron iii solid state electrolytes for wearable thermo Electrochemical Cells
    Electrochemistry Communications, 2021
    Co-Authors: Yuetong Zhou, Yuqing Liu, Mark A Buckingham, Shuai Zhang, Leigh Aldous, Stephen Beirne, Gordon G Wallace, Jun Chen
    Abstract:

    Abstract Thermo-Electrochemical Cells (known as thermoCells) can convert heat energy into electrical power through redox reactions driven by the presence of a temperature gradient. Low-grade heat from the human body can be harvested using thermoCells containing a suitable electrolyte, such as the iron(II)/iron(III) chloride redox couple housed in poly (vinyl alcohol) described here. However, conventionally the thermo-Electrochemical performance of gelled electrolytes is poor, due to slow ionic transport and high charge transfer resistance. In this report, hydrochloric acid has been found to synergistically decrease the charge transfer resistance of the redox reaction, whilst doubling the tensile properties of the gel housing. Moreover, individual thermoCells can be connected in parallel to enhance current output.

  • Potentially Wearable Thermo‐Electrochemical Cells for Body Heat Harvesting: From Mechanism, Materials, Strategies to Applications
    'Wiley', 2021
    Co-Authors: Yuqing Liu, Hongbo Wang, Peter C. Sherrell, Lili Liu, Yong Wang, Jun Chen
    Abstract:

    Abstract Wearable electronics are becoming one of the key technologies in health care applications including health monitoring, data acquisitions, and real‐time diagnosis. The commercialization of next‐generation devices has been stymied by the lack of ultrathin, flexible, and reliable power sources. Wearable thermo‐Electrochemical Cells (TECs), which can convert body heat to electricity via an Electrochemical process, are showing great promise as power sources for such wearable systems. TECs harvest orders of magnitude more voltage per temperature difference (Seebeck coefficient (1–34 mV K−1)) when compared to the more common thermoelectric generators (Seebeck coefficient ≈tens or hundreds of µV K−1). However, there still remain great challenges for TECs progressing towards wearable applications. This review summarizes the recent development of potentially wearable TECs with promise for body‐heat harvesting, with a specific focus on flexible electrode materials, solid‐state electrolytes, device fabrication, and strategies toward applications. It also clarifies the challenges and gives some future direction to enhance future investigations on high‐performance wearable TECs for practical and self‐powered wearable devices