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  • 1.
    Auroux, Etienne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Huseynova, Gunel
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Miranda la Hera, Vladimir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    A metal-free and transparent light-emitting device by sequential spray-coating fabrication of all layers including PEDOT:PSS for both electrodes2023In: RSC Advances, E-ISSN 2046-2069, Vol. 13, no 25, p. 16943-16951Article in journal (Refereed)
    Abstract [en]

    The concept of a metal-free and all-organic electroluminescent device is appealing from both sustainability and cost perspectives. Herein, we report the design and fabrication of such a light-emitting electrochemical cell (LEC), comprising a blend of an emissive semiconducting polymer and an ionic liquid as the active material sandwiched between two poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) conducting-polymer electrodes. In the off-state, this all-organic LEC is highly transparent, and in the on-state, it delivers uniform and fast to turn-on bright surface emission. It is notable that all three device layers were fabricated by material- and cost-efficient spray-coating under ambient air. For the electrodes, we systematically investigated and developed a large number of PEDOT:PSS formulations. We call particular attention to one such p-type doped PEDOT:PSS formulation that was demonstrated to function as the negative cathode, as well as future attempts towards all-organic LECs to carefully consider the effects of electrochemical doping of the electrode in order to achieve optimum device performance.

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  • 2.
    Auroux, Etienne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Huseynova, Gunel
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Miranda la Hera, Vladimir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Metal-free and transparent light-emitting devices fabricated by sequentialspray coatingManuscript (preprint) (Other academic)
  • 3.
    Auroux, Etienne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Park, So-Ra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå University, Umeå, Sweden.
    Ion transfer into solution-processed electrodes can significantly shift the p-n junction and emission efficiency of light-emitting electrochemical cells2022In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 121, no 23, article id 231102Article in journal (Refereed)
    Abstract [en]

    A light-emitting electrochemical cell (LEC) comprises mobile ions in its active material, which enable for in situ formation of a p-n junction by electrochemical doping. The position of this emissive p-n junction in the interelectrode gap is important, because it determines whether the emission is affected by constructive or destructive interference. An appealing LEC feature is that the entire device can be fabricated by low-cost solution-based printing and coating. Here, we show, somewhat unexpectedly, that the replacement of conventional vacuum-deposited indium-tin-oxide (ITO) for the positive anode with solution-processed poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) can result in an increase in the peak light-emission output by 75%. We demonstrate that this emission increase is due to that the p-n junction shifts from a position of destructive interference in the center of the interelectrode gap with ITO to a position of constructive interference closer to the anode with PEDOT:PSS. We rationalize the anodic p-n junction shift by significant anion transfer into the soft and porous PEDOT:PSS electrode during LEC operation, which is prohibited for the ITO electrode because of its compact and hard nature. Our study, thus, contributes with important design criteria for the attainment of efficient light emission from solution-processed LEC devices.

  • 4.
    Huseynova, Gunel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Auroux, Etienne
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Huang, Ping
    Department of Chemistry, Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Chemical doping to control the in-situ formed doping structure in light-emitting electrochemical cells2023In: Scientific Reports, E-ISSN 2045-2322, Vol. 13, no 1, article id 11457Article in journal (Refereed)
    Abstract [en]

    The initial operation of a light-emitting electrochemical cell (LEC) constitutes the in-situ formation of a p-n junction doping structure in the active material by electrochemical doping. It has been firmly established that the spatial position of the emissive p-n junction in the interelectrode gap has a profound influence on the LEC performance because of exciton quenching and microcavity effects. Hence, practical strategies for a control of the position of the p-n junction in LEC devices are highly desired. Here, we introduce a "chemical pre-doping" approach for the rational shifting of the p-n junction for improved performance. Specifically, we demonstrate, by combined experiments and simulations, that the addition of a strong chemical reductant termed "reduced benzyl viologen" to a common active-material ink during LEC fabrication results in a filling of deep electron traps and an associated shifting of the emissive p-n junction from the center of the active material towards the positive anode. We finally demonstrate that this chemical pre-doping approach can improve the emission efficiency and stability of a common LEC device.

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  • 5.
    Larsen, Christian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    Lundberg, Petter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Andreas
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    Lindh, E. Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    A tool for identifying green solvents for printed electronics2021In: Nature Communications, E-ISSN 2041-1723, Vol. 12, article id 4510Article in journal (Refereed)
    Abstract [en]

    The emerging field of printed electronics uses large amounts of printing and coating solvents during fabrication, which commonly are deposited and evaporated within spaces available to workers. It is in this context unfortunate that many of the currently employed solvents are non-desirable from health, safety, or environmental perspectives. Here, we address this issue through the development of a tool for the straightforward identification of functional and "green" replacement solvents. In short, the tool organizes a large set of solvents according to their Hansen solubility parameters, ink properties, and sustainability descriptors, and through systematic iteration delivers suggestions for green alternative solvents with similar dissolution capacity as the current non-sustainable solvent. We exemplify the merit of the tool in a case study on a multi-solute ink for high-performance light-emitting electrochemical cells, where a non-desired solvent was successfully replaced by two benign alternatives. The green-solvent selection tool is freely available at: www.opeg-umu.se/green-solvent-tool.

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  • 6.
    Liu, Yong-feng
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. College of Physical Science and Technology, Yangzhou University, Yangzhou, China; Microelectronics Industry Research Institute, Yangzhou University, Yangzhou, China.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gao, Zhaoju
    College of Physical Science and Technology, Yangzhou University, Yangzhou, China.
    Shao, Xiuwen
    College of Physical Science and Technology, Yangzhou University, Yangzhou, China.
    Zhu, Xiaoling
    College of Physical Science and Technology, Yangzhou University, Yangzhou, China.
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    The influence of the capping ligands on the optoelectronic performance, morphology, and ion liberation of CsPbBr3 perovskite quantum dots2023In: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 16, no 7, p. 10626-10633Article in journal (Refereed)
    Abstract [en]

    Perovskite quantum dots (PeQDs) endowed with capping ligands exhibit impressive optoelectronic properties and enable for cost-efficient solution processing and exciting application opportunities. We synthesize and characterize three different PeQDs with the same cubic CsPbBr3 core, but which are distinguished by the ligand composition and density. PeQD-1 features a binary didodecyldimethylammonium bromide (DDAB) and octanoic acid capping ligand system, with a high surface density of 1.53 nm−2, whereas PeQD-2 and PeQD-3 are coated by solely DDAB at a gradually lower surface density. We show that PeQD-1 endowed with highest ligand density features the highest dispersibility in toluene of 150 g/L, the highest photoluminescence quantum yield of 95% in dilute solution and 59% in a neat film, and the largest core-to-core spacing in neat thin films. We further establish that ions are released from the core of PeQD-1 when it is exposed to an electric field, although it comprises a dense coating of one capping ligand per four surface core atoms. We finally exploit these combined findings to the development of a light-emitting electrochemical cell (LEC), where the active layer is composed solely of solution-processed pure PeQDs, without additional electrolytes. In this device, the ion release is utilized as an advantage for the electrochemical doping process and efficient emissive operation of the LEC.

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  • 7. Mone, Mariza
    et al.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Genene, Zewdneh
    Murto, Petri
    Jevric, Martyn
    Zou, Xianshao
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Abdulahi, Birhan A.
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mammo, Wendimagegn
    Andersson, Mats R.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Ergang
    Near-Infrared Emission by Tuned Aggregation of a Porphyrin Compound in a Host-Guest Light-Emitting Electrochemical Cell2021In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 9, no 6, article id 2001701Article in journal (Refereed)
    Abstract [en]

    The synthesis of 5,10,15,20-tetrakis((5,10-bis((2-hexyldecyl)oxy)dithieno[3,2-c:3′,2′-h][1,5]naphthyridin-2-yl)ethynyl)porphyrin zinc(II) (Por4NT), a near-infrared (NIR) emitting compound, comprising a zinc porphyrin core linked with triple bonds through its meso positions to four 5,10-bis((2-hexyldecyl)oxy)dithieno[3,2-c:3′,2′-h][1,5]naphthyridine (NT) arms is reported. Por4NT featured high solubility in common non-polar solvents, which is ideal for easy processing through solution techniques, and high photoluminescence (PL) efficiency of ≈30% in dilute toluene solution. It also exhibited a strong tendency for aggregation because of its flat conformation, and this aggregation resulted in a strong redshifted emission and a drop in PL efficiency. A well-matched PBDTSi-BDD-Py "host" terpolymer is therefore designed, which is capable of mitigating the aggregation of the Por4NT "guest". An optimized blend of the host, guest, and an ionic-liquid electrolyte is utilized as the active material in a light-emitting electrochemical cell (LEC), which delivered strong NIR radiance of 134 µW cm-2 with a long wavelength maximum at 810 nm at a low drive voltage of 5.0 V. The attainment of the strong NIR emission from the host–guest LEC is attributed to a tuned aggregation of the Por4NT emitter, which resulted in the desired aggregation-induced redshift of the emission at a reasonably retained efficiency.

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  • 8.
    Ràfols-Ribé, Joan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jenatsch, Sandra
    Lundberg, Petter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Andreas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Elucidating Deviating Temperature Behavior of Organic Light-Emitting Diodes and Light-Emitting Electrochemical Cells2021In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 9, no 1, article id 2001405Article in journal (Refereed)
    Abstract [en]

    Organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs) exhibit different operational modes that render them attractive for complementary applications, but their dependency on the device temperature has not been systematically compared. Here, the effects of a carefully controlled device temperature on the performance of OLEDs and LECs based on two common emissive organic semiconductors are investigated. It is found that the peak luminance and current efficacy of the two OLEDs are relatively temperature independent, whereas, the corresponding LECs exhibit a significant increase by approximate to 85% when the temperature is changed from 20 to 80 degrees C. A combination of simulations and measurements reveal that this deviating behavior is consistent with a shift of the emission zone from closer to the transparent anode toward the center of the active material for both the OLEDs and the LECs, which in turn can be induced by a stronger positive temperature dependence of the mobility of the holes than the electrons.

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  • 9.
    Ràfols-Ribé, Joan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hänisch, Christian
    Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP), Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    Reineke, Sebastian
    Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP), Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    In situ determination of the orientation of the emissive dipoles in light-emitting electrochemical cells2023In: Advanced Materials Technologies, E-ISSN 2365-709X, Vol. 8, no 13, article id 2202120Article in journal (Refereed)
    Abstract [en]

    The orientation of the emissive dipoles in thin-film devices is important since it strongly affects the light outcoupling and thereby the device emission efficiency. The light-emitting electrochemical cell (LEC) is particularly interesting in this context because its emissive dipoles are located in a high electric-field p-n junction, which is formed in situ by redistribution of bulky ions. This implies that the dipole orientation could be distinctly different in the driven LEC compared to the pristine device. This study develops the destructive-interference microcavity method for the accurate in situ determination of the orientation of the emissive dipoles during LEC operation and apply it on a common LEC device comprising an amorphous conjugated polymer termed Super Yellow as the emitter. It is found that ≈95% of the emissive dipoles are oriented in the horizontal direction with respect to the thin-film plane in both the pristine LEC and during steady-state light emission. This finding is attractive since it enables for efficient outcoupling of the generated photons, and interesting because it shows that a horizontal orientation of the emissive dipoles can remain despite the existence of a strong perpendicular electric field and the nearby motion of bulky ions during LEC operation.

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  • 10.
    Ràfols-Ribé, Joan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Robinson, Nathaniel D.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Top, Michiel
    Sandström, Andreas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Self-Heating in Light-Emitting Electrochemical Cells2020In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 30, no 33, article id 1908649Article, review/survey (Refereed)
    Abstract [en]

    Electroluminescent devices become warm during operation, and their performance can, therefore, be severely limited at high drive current density. Herein, the effects of this self‐heating on the operation of a light‐emitting electrochemical cell (LEC) are systematically studied. A drive current density of 50 mA cm−2 can result in a local device temperature for a free‐standing LEC that exceeds 50 °C within a short period of operation, which in turn induces premature device degradation as manifested in the rapidly decreasing luminance and increasing voltage. Furthermore, this undesired self‐heating for a free‐standing thin‐film LEC can be suppressed by the employment of a device architecture featuring high thermal conductance and a small emission‐area fill factor, since the corresponding improved heat conduction to the nonemissive regions facilitates more efficient heat transfer to the ambient surroundings. In addition, the reported differences in performance between small‐area and large‐area LECs as well as between flexible‐plastic and rigid‐glass LECs are rationalized, culminating in insights that can be useful for the rational design of LEC devices with suppressed self‐heating and high performance.

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  • 11.
    Ràfols-Ribé, Joan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhang, Xiaoying
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lundberg, Petter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lindh, E. Mattias
    RISE Energy Technology Center AB, Piteå, Sweden.
    Mai, Cuc Thu
    Department of Chemistry − Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Mindemark, Jonas
    Department of Chemistry − Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Controlling the emission zone by additives for improved light‐emitting electrochemical cells2022In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 34, no 8, article id 2107849Article in journal (Refereed)
    Abstract [en]

    The position of the emission zone (EZ) in the active material of a light-emitting electrochemical cell (LEC) has a profound influence on its performance because of microcavity effects and doping- and electrode-induced quenching. Previous attempts of EZ control have focused on the two principal constituents in the active material—the organic semiconductor (OSC) and the mobile ions—but this study demonstrates that it is possible to effectively control the EZ position through the inclusion of an appropriate additive into the active material. More specifically, it is shown that a mere modification of the end group on an added neutral compound, which also functions as an ion transporter, results in a shifted EZ from close to the anode to the center of the active material, which translates into a 60% improvement of the power efficiency. This particular finding is rationalized by a lowering of the effective electron mobility of the OSC through specific additive: OSC interactions, but the more important generic conclusion is that it is possible to control the EZ position, and thereby the LEC performance, by the straightforward inclusion of an easily tuned additive in the active material.

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  • 12.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    dos Santos, John Marques
    Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, St Andrews, United Kingdom.
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zysman-Colman, Eli
    Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, St Andrews, United Kingdom.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Introducing MR-TADF emitters into light-emitting electrochemical cells for narrowband and efficient emission2023In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 33, article id 2306170Article in journal (Refereed)
    Abstract [en]

    Organic semiconductors that emit by the process of multi-resonance thermally activated delayed fluorescence (MR-TADF) can deliver narrowband and efficient electroluminescence while being processable from solvents and metal-free. This renders them attractive for use as the emitter in sustainable light-emitting electrochemical cells (LECs), but so far reports of narrowband and efficient MR-TADF emission from LEC devices are absent. Here, this issue is addressed through careful and systematic material selection and device development. Specifically, the authors show that the detrimental aggregation tendency of an archetypal rigid and planar carbazole-based MR-TADF emitter can be inhibited by its dispersion into a compatible carbazole-based blend host and an ionic-liquid electrolyte, and it is further demonstrated that the tuning of this active material results in a desired balanced p- and n-type electrochemical doping, a high solid-state photoluminescence quantum yield of 91%, and singlet and triplet trapping on the MR-TADF guest emitter. The introduction of this designed metal-free active MR-TADF material into a LEC, employing air-stabile electrodes, results in bright blue electroluminescence of 500 cd m−2, which is delivered at a high external quantum efficiency of 3.8% and shows a narrow emission profile with a full-width-at-half-maximum of 31 nm.

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  • 13.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    An Amorphous Spirobifluorene-Phosphine-Oxide Compound as the Balanced n-Type Host in Bright and Efficient Light-Emitting Electrochemical Cells with Improved Stability2021In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 9, no 7, article id 2002105Article in journal (Refereed)
    Abstract [en]

    A rational host–guest concept design for the attainment of high efficiency at strong luminance from light‐emitting electrochemical cells (LECs) by suppression of exciton‐polaron quenching [Tang et al., Nature Communications 20178, 1190] has been reported. However, a practical drawback with the presented host–guest LEC devices was that the operational stability is insufficient for many applications. Here, a systematic study is performed, revealing that a major culprit for the limited operational stability is that the employed n‐type host, 1,3‐bis[2‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazo‐5‐yl]benzene (OXD‐7), has a strong propensity for crystallization and that this crystallization results in a detrimental phase separation of the constituents in the active material during device operation. The authors, therefore, identify an alternative class of concept‐functional n‐type hosts in the form of spirobifluorene‐phosphine‐oxide compounds, and report that the replacement of OXD‐7 with amorphous 2,7‐bis(diphenylphosphoryl)‐9,9′‐spirobifluorene results in a much improved operational lifetime of 700 h at >100 cd m−2 during constant‐bias driving at an essentially retained high current efficacy of 37.9 cd A−1 and a strong luminance of 2940 cd m−2.

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  • 14.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    Lundberg, Petter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tsuchiya, Youichi
    Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, Motooka, Nishi-ku, Fukuoka, Japan.
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    Liu, Yong-feng
    Umeå University, Faculty of Science and Technology, Department of Physics. College of Physical Science and Technology & Microelectronics Industry Research Institute, Yangzhou University, Yangzhou, China.
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Adachi, Chihaya
    Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, Motooka, Nishi-ku, Fukuoka, Japan.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    Efficient and bright blue thermally activated delayed fluorescence from light-emitting electrochemical cells2022In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, no 44, article id 2205967Article in journal (Refereed)
    Abstract [en]

    Light-emitting electrochemical cells (LECs) comprising metal-free molecules that emit by the process of thermally activated delayed fluorescence (TADF) can be both sustainable and low cost. However, the blue emission performance of current TADF-LECs is unfortunately poor, which effectively prohibits their utilization in important applications, such as illumination and full-color displays. Here, this drawback is addressed through the development of a TADF-LEC, which delivers blue light emission (peak wavelength = 475 nm) with a high external quantum efficiency of 5.0%, corresponding to a current efficacy of 9.6 cd A-1. It is notable that this high efficiency is attained at bright luminance of 740 cd m-2, and that the device turn-on is very fast. It is demonstrated that this accomplishment is enabled by the blending of a carbazole-based 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-methylphenyl)-3,6-dimethyl-9H-carbazole guest emitter with a compatible carbazole-based tris(4-carbazoyl-9-ylphenyl)amine:2,6-bis(3-(carbazol-9-yl)phenyl)pyridine blend-host for the attainment of bipolar electrochemical doping, balanced electron/hole transport, and exciplex-effectuated host-to-guest energy transfer.

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  • 15. Vila-Costa, A.
    et al.
    Ràfols-Ribé, Joan
    Grup de Nanomaterials i Microsistemes, Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain.
    Gonzalez-Silveira, M.
    Lopeandia, A.
    Tamarit, J. Ll
    Rodriguez-Viejo, J.
    Multiple glass transitions in vapor-deposited orientational glasses of the most fragile plastic crystal Freon 1132019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 20, p. 10436-10441Article in journal (Refereed)
    Abstract [en]

    We investigate by fast-scanning nanocalorimetry the formation of Freon 113 films from the vapor phase at deposition temperatures ranging from 50 to 120 K, that is, spanning above and below the transition temperature of the glassy crystal to the plastic crystal (T-gc = 72 K). Analysis of the heat capacity curves indicates that vapor deposition at T < T-gc of the highly fragile Freon 113 yields structural and orientational glasses in the as-deposited state depending on the temperature range of deposition. Interestingly, growing above T-gc produces plastic crystals with a conformational ratio C-1/C-s that changes with T-dep above and below 110-120 K, the temperature at which previous works have identified the arrest of the transformations between the C-1 and C-s conformers.

  • 16. Vila-Costa, A.
    et al.
    Ràfols-Ribé, Joan
    Group of Nanomaterials and Microsystems, Physics Department, Universitat Autònoma de Barcelona, Bellaterra, Spain.
    González-Silveira, M.
    Lopeandia, A. F.
    Abad-Muñoz, Ll.
    Rodriguez-Viejo, J.
    Nucleation and Growth of the Supercooled Liquid Phase Control Glass Transition in Bulk Ultrastable Glasses2020In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 124, no 7, article id 076002Article in journal (Refereed)
    Abstract [en]

    We report the anomalous bulk transformation of vapor deposited stable glasses into the liquid state. The transformation proceeds through two competing parallel processes: partial rejuvenation of the stable glass and nucleation and growth of liquid patches within the glass. The kinetics of the transformation extracted from heat capacity curves after isothermal runs is dominated by the heterogeneous nucleation and growth process that initiates at preexisting seeds and propagates radially at a velocity proportional to the alpha relaxation time. Remarkably, the distance between the activation seeds is independent of temperature within experimental uncertainty and amounts to several micrometers, a value in close agreement with the crossover length for TPD glasses. We speculate the initiation sites for the transformation of the glass into the supercooled liquid are localized regions of lower stability (or density).

  • 17.
    Zhang, Xiaoying
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ràfols-Ribé, Joan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mindemark, Jonas
    Department of Chemistry − Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lindh, Mattias
    Sustainable Resource Conversion unit, Biorefinery and Energy department, RISE Research Institutes of Sweden AB, Storgatan 65, Umeå, Sweden.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Efficiency roll-off in light-emitting electrochemical cells2024In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095Article in journal (Refereed)
    Abstract [en]

    Understanding “efficiency roll-off” (i.e., the drop in emission efficiency with increasing current) is critical if efficient and bright emissive technologies are to be rationally designed. Emerging light-emitting electrochemical cells (LECs) can be cost- and energy-efficiently fabricated by ambient-air printing by virtue of the in situ formation of a p-n junction doping structure. However, this in situ doping transformation renders a meaningful efficiency analysis challenging. Herein, a method for separation and quantification of major LEC loss factors, notably the outcoupling efficiency and exciton quenching, is presented. Specifically, the position of the emissive p-n junction in common singlet-exciton emitting LECs is measured to shift markedly with increasing current, and the influence of this shift on the outcoupling efficiency is quantified. It is further verified that the LEC-characteristic high electrochemical-doping concentration renders singlet-polaron quenching (SPQ) significant already at low drive current density, but also that SPQ increases super-linearly with increasing current, because of increasing polaron density in the p-n junction region. This results in that SPQ dominates singlet-singlet quenching for relevant current densities, and significantly contributes to the efficiency roll-off. This method for deciphering the LEC efficiency roll-off can contribute to a rational realization of all-printed LEC devices that are efficient at highluminance.

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