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Advances in thin film light-emitting devices have fueled the rapid growth of a new class of solid-state lighting devices, featuring low fabrication cost, high quantum efficiency, and broadband spectrum coverage, etc. In contrast to the conventional inorganic semiconductors that rely on lattice matched high crystalline quality substrate, solution processable thin films eliminate the dependence on the substrate, which is highly desired for the ease and versatility of integrations with foreign medium. By taking this advantage, this work developed an ultracompact solution to control the directionality of thin film emitters using integrated dielectric metasurface through one step spin-coating process. As a proof of concept, directional emissions from perovskite nanocrystal thin film, including collimated light emissions and two-dimensional beam steering, are experimentally demonstrated. Notably, our approach, where light emitters were integrated on the back side of substrate after the fabrication of metasurface, judiciously avoids any potential degradation of material optical quality caused by the multi-step nanofabrication. Therefore, it can serve as a generalized scheme to engage the advantageous properties of dielectric metasurface, including the compactness, high efficiency, and beam controllability with the emerging thin film light-emitting diodes (LEDs), which is applicable to a wide range of solution processable materials, including organic light-emitting diodes, quantum-dot light emitting diodes, polymer LEDs, and perovskite LEDs, opening up new pathways to develop low-cost and ultra-compact solid state light sources with versatile beams characteristics. [ABSTRACT FROM AUTHOR]

The inkjet printing method is a promising method to deposit polymer and functional nanoparticles at the microscale. It can be applied in the fabrication of multicolor polymer light emitting diodes (polyLEDs), polymer base electronics, multicolor color conversion layers, and quantum dot light emitting diodes (QLEDs). One of the main challenges is to print high-resolution polymer dots from dilute polymer solution. In addition, the quality of printed multicolor polyLEDs, QLEDs and multicolor color conversion layers is currently limited by non-uniformity of the printed dots. In this paper, polydimethylsiloxane (PDMS) is selected as the functional polymer, due to its high transparency, good reflective index value, inflammable and flexible properties. The optimal ink to form a uniform PDMS dot array is presented in this paper. Both the solvent and PDMS were tuned to form the uniform PDMS dot array. The uniform PDMS dot array was printed with a diameter of around 50 µm, and the array of closely spaced green quantum dots (QDs) mixed with PDMS ink was also printed on the substrate uniformly. While the green QD-PDMS film was printed at a resolution of 1693 dpi, the uniformity was evaluated using the photoluminescence (PL) spectrum and color coordinate value. [ABSTRACT FROM AUTHOR]

Organic/polymer light-emitting diodes (OLEDs/PLEDs) have attracted a rising number of investigations due to their promising applications for high-resolution fullcolor displays and energy-saving solid-state lightings. Near-infrared (NIR) emitting dyes have gained increasing attention for their potential applications in electroluminescence and optical imaging in optical tele-communication platforms, sensing and medical diagnosis in recent decades. And a growing number of people focus on the "heavy metal-free" NIR electroluminescent materials to gain more design freedom with cost advantage. This review presents recent progresses in conjugated polymers and organic molecules for OLEDs/PLEDs according to their different luminous mechanism and constructing systems. The relationships between the organic fluorophores structures and electroluminescence properties are the main focus of this review. Finally, the approaches to enhance the performance of NIR OLEDs/PLEDs are described briefly. We hope that this review could provide a new perspective for NIR materials and inspire breakthroughs in fundamental research and applications. [ABSTRACT FROM AUTHOR]

Herein are reported the syntheses of poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PF), poly(9,9-dioctylfluorene-alt-benzothiadiazole) (PFBT), and poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) by employing catalytic mechanochemical Suzuki polymerization in a ball mill. This mechanochemical synthesis technique can yield soluble functionalized polyfluorenes and its derivatives in 30 min or less. Furthermore, the polymer light emitting diode and photovoltaic interfacial electrolyte, poly(9,9-bis(3′-(N,N-dimethyl)-N-ethylammoinium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluprene))dibromide (PFN-Br), was obtained via a facile mechanochemical quaternization reaction at the terminal amino groups of PFN. [ABSTRACT FROM AUTHOR]

Polymer light‐emitting electrochemical cells (PLECs) and light‐emitting diodes (PLEDs) receive interest for large‐area lighting and signage applications. During operation of a PLEC, a p–i–n junction develops where electrons and holes are injected into the film and are transported along n‐ and p‐doped regions to the intrinsic (i) region, where they recombine under light emission. Conceptually, this resembles the PLED device architecture equipped with Ohmic charge‐injection and transport layers. The similarity between the i‐region of the PLEC and the emissive layer of the PLED is obvious; however, implication of this has not been examined in detail so far. For example, for PLEDs it is known that electron traps hinder the electron transport, and that hole trap formation dictates the long‐term durability. Here, for PLECs the electrical and optical response to electrical driving and breaks are studied, the current response to external light irradiation is probed, and degradation is followed with long‐term absorption and capacitance measurements. The electron traps in PLECs are identified and it is found that hole trap formation limits the device lifetime, in the same manner as established for PLEDs. It is concluded that charge traps in semiconducting polymers present important, but so far overlooked intrinsic performance limitations for PLECs. [ABSTRACT FROM AUTHOR]

Semiconducting polymers are being studied intensively for optoelectronic device applications, including solution‐processed light‐emitting diodes (PLEDs). Charge traps in polymers limit the charge transport and thus the PLED efficiency. It is firmly established that electron transport is hindered by the presence of the universal electron trap density, whereas hole trap formation governs the long‐term degradation of PLEDs. Here, the response of PLEDs to electrical driving and breaks covering the timescale from microseconds to (a few) hours is studied, thus focusing on electron traps. As reference polymer, a phenyl‐substituted poly(para‐phenylene vinylene) (PPV) copolymer termed super yellow (SY) is used. Three different traps with depths between ≈0.4 and 0.7 eV, and a total trap site density of ≈2 × 1017 cm−3 are identified. Surprisingly, filling of deep traps takes minutes to hours, at odds with the common notion that charge trapping is complete after a few hundred microseconds. The slow trap filling feature for PLEDs is confirmed using poly(2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene (MEH‐PPV) and poly(3‐hexylthiophene) (P3HT) as active materials. This unusual phenomenon is explained with trap deactivation upon detrapping and slow trap reactivation. The results provide useful insight to pinpoint the chemical nature of the universal electron traps in semiconducting polymers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optoelectronic behavior of the nanocomposite material MEH-PPV/Al 2 O 3 was studied and analyzed. • There is a critical volume of filler changing the structural ordering of thin composite films. • Optoelectronic properties, luminance and operational time of PLED are related to these changes. • Results allow a more detailed description of LED prepared from nanocomposite active layers. This work presents the effect of nanofiller (Al 2 O 3) in the polymer matrix MEH-PPV - Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] on optical, optoelectronic, and electrical properties. These properties were investigated using UV–Vis absorption, and photoluminescence spectroscopy. Exciton diffusion length was examined using the surface photovoltage (SPV) method, mobility of charge carriers was evaluated with charge extraction by linearly increasing voltage (CELIV) measurements. Information concerning the band structure was obtained using energy resolved-electrochemical impedance spectroscopy (ER-EIS). The influence of nanoparticles on the development of the micro structure in thin layers was examine with grazing-incidence wide-angle X-ray scattering (GIWAXS). Prepared nanocomposite thin films were subsequently used as active layers in polymer light-emitting diodes. Luminance, current efficiency, and stability of prepared polymer light emitting diodes were tested. The presented work clarifies the effect of non-conductive nanofiller on the properties of the polymer matrix and on the performance of OLEDs with an active layer made of nanocomposite material. [ABSTRACT FROM AUTHOR]

The fast degradation of polymer light-emitting diodes (PLEDs) in ambient conditions is primarily due to the oxidation of highly reactive metals, such as barium or calcium, which are used as cathode materials. Here, we report the fabrication of PLEDs using an air-stable partially oxidized aluminum (AlOx) cathode. Usually, the high work function of aluminum (4.2 eV) imposes a high barrier for injecting electrons into the lowest unoccupied molecular orbital (LUMO) of the emissive polymer (2.9 eV below the vacuum level). By partially oxidizing aluminum, its work function is decreased, but not sufficiently low for efficient electron injection. Efficient injection is obtained by inserting an electron transport layer of poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT), which has its LUMO at 3.3 eV below vacuum, between the AlOx cathode and the emissive polymer. The intermediate F8BT layer not only serves as a hole-blocking layer but also provides an energetic staircase for electron injection from AlOx into the emissive layer. PLEDs with an AlOx cathode and F8BT interlayer exhibit a doubling of the efficiency as compared to conventional Ba/Al PLEDs, and still operate even after being kept in ambient atmosphere for one month without encapsulation. [ABSTRACT FROM AUTHOR]

The authors present white polymer light-emitting electrochemical cells (PLECs) fabricated with polymer blend films of poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD) and π-conjugated triphenylamine molecules. The PLECs have bulk heterojunction structures composed of van der Waals interfaces between the PFD segments and the amine molecules. White-light electroluminescence (EL) can be achieved via light-mixing of the blue exciton emission from PFD and long-wavelength exciplex emission from excited complexes consisting of PFD segments (acceptors (As)) and the amine molecules (donors (Ds)). Precise control of the distances between the PFD and the amine molecules, affected through proper choice of the concentrations of PFD, amine molecules, and polymeric solid electrolytes, is critical to realizing white emission. White PLECs can be fabricated with PFD and amine molecules whose highest occupied molecular orbital (HOMO) levels range from –5.3 eV to –5.0 eV. Meanwhile, PLECs fabricated with amine molecules whose HOMO levels are lower than –5.6 eV cannot produce exciplex emission. The distances between the PFD and amine molecules of the exciplexes appear to be larger than 0.4 nm. These experimental data are explained by perturbation theory using the charge-transfer state (A–D+), the locally excited state (A*D), which is assumed to be the locally excited acceptor state in which there is no interaction with the donor molecule; and the energy gap between the HOMO levels of the PFD and the amine molecules. Color-stable white PLECs were fabricated using 4,4',4"-tris[N-(2-naphthyl)-N-phenylamino]- triphenylamine, which has a HOMO level of –5.2 eV, as the amine molecule, and the color stability of the device is a function of the fact that PFD forms exciplexes with these molecules. [ABSTRACT FROM AUTHOR]

Efficient single-layer organic light-emitting diodes (OLEDs) were reported based on a green fluorescent dye 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1) benzopyropyrano (6,7-8-I,j)quinolizin-11-one (C545T). Herein, poly(3,4-ethylenedioxy thiophene) poly(styrene sulfonate) were, respectively, applied as the injection layer for comparison. The hole transport properties of the emission layer with different hole injection materials are well investigated via current-voltage measurement. It was clearly found that the hole injection layers (HILs) play an important role in the adjustment of the electron/hole injection to attain transport balance of charge carriers in the single emission layer of OLEDs with electron-transporting host. The layer of tris-(8-hydroxyquinoline) aluminum played a dual role of host and electron-transporting materials within the emission layer. Therefore, appropriate selection of hole injection layer is a key factor to achieve high efficiency OLEDs with single emission layer. [ABSTRACT FROM AUTHOR]

Mesopolymers with high solubility, free of structural defects, and negligible batch‐to‐batch variation open a new avenue for organic optoelectronics. Organic light emitting transistors that combine the functions of organic light‐emitting diodes and organic field‐effect transistors. However, charge transport ability and light emitting strength are contradictory within one conjugated polymer. Herein, three low‐molecular‐weight mesopolymers with thienopyrroledione–benzothiadiazole repeating units (meso‐TBTF) were obtained. The mesopolymers show strong solid‐state emission and high ambipolar carrier mobility. The molecular weights of meso‐TBTF can be tuned by polymerization temperature. The mesopolymers have photoluminescence quantum yields (PLQY) of about 50 % in solution and 10 % in solid state. Polymer light emitting diodes of this material are fabricated to explore its potential use in optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract Three novel conjugated polymers based on 9,9′‐dioctylfluorene unit and isoindolo[2,1‐a]benzimidazol‐11‐one with different fluorine substituents (0, 2 and 4) were synthesized. PLED and resistive memory devices based on these polymers were prepared consequently. PLED based on four‐fluorinated polymer showed the highest maximum brightness of 3192 cd m−2 with almost 5‐fold increase of current efficiency 8‐fold increase of external quantum efficiency compared to that of the other two, and all the PLEDs exhibited good emission stability with no noticeable change of electroluminescence even under high voltage of 10 V. The memory device of doubly‐fluorinated polymer exhibited ternary flash behavior with threshold voltages below −2.5 V, while device of four‐fluorinated polymer possessed ON/OFF current ratio above 104. Impact of fluorine substitutions on the performance of devices were briefly investigated. The results revealed that the improvement of device performance might not scale with the increasing number of fluorine substitutions, and the four‐fluorine‐substituted polymer and doubly‐fluorinated polymer could be encouraging materials for applications of PLED and resistive memory device and worth of further design of other new polymer systems.

Abstract White organic/polymer light emitting diode (WOLED/WPLED) processed from solution has attracted significant research interest in recent years due to their low device production cost, device flexibility, easy fabrication over large area including roll to roll and ability to print in various designs and shapes providing enormous design possibilities. Although WOLEDs fabricated using solution process lack their thermally evaporated counterparts in terms of device efficiency, remarkable progress has been made in this regard in recent years by utilizing new materials and device structures. In the present review, we have summarized and extrapolated an excellent association of old and modern concept of cost-effective materials and device structure for realization of white light. In particular, this article demonstrated and focused on design, and development of novel synthesis strategy, mechanistic insights and device engineering for solution process low cost WOLEDs device. Herein, an overview of the prevailing routes towards white light emitting devices (WLEDs) and corresponding materials used, including polymer based WLED, small molecules emitters based thermally activated delayed fluorescence (TADF), perovskite light-emitting diodes (PeLEDs) and hybrid materials based LEDs, color down-converting coatings with corresponding best efficiencies ever realized. We presume that this exhaustive review on WLEDs will offer a broad overview of the latest developments on white SSL and stonework the approach en route for innovations in the immediate future.

In this article, we have demonstrated the hybrid polymer light-emitting diodes (PLEDs) with a sol-gel derived or rf-sputtered ZnO electron transport layer (ETL). For the ZnO films prepared under different conditions, low annealing temperature (300 °C) leads to the film amorphous while the polycrystalline films is readily achieved by sputtering. Though the surface roughness can be improved by thermal annealing at 400 °C for sputtered films, the release of compressive stress after treatment has shrunk the optical band gap from 3.282 to 3.268 eV. As the ETL in PLEDs, the reduced band gap could increase potential barrier for electron injection and decrease the hole blocking capability. In our cases, luminance larger than 7000 cd/m² can be obtained in device with pristine sputtered ZnO ETL. It is concluded that crystalline structure of ZnO films is important to facilitate the balance of carrier mobility to obtain high luminance and high efficiency devices. [ABSTRACT FROM AUTHOR]

A series of poly (aryl ether) based bipolar polymer hosts, PCzOPOC8, PCzOPOCz, and PCzOPOCN with a peripheral carbazole or cyano unit which joins the main chain by a nonconjugated linker of a hexyl group, were synthesized and characterized. They depicted high triplet level (ET) (>2.80 eV), which was probably attributed to oxygen‐interrupted nonconjugated main chains of polymers as well as carbazole and phosphine oxide groups with high ET. While doped with a 10 wt% typical blue phosphor {iridium(III)[bis(4,6‐difluoro phenyl)pyridinato‐N, C2]picolinate, FIrpic)}, compared with those of nonsubstituted PCzOPOC8 and peripheral cyano‐substituted PCzOPOCN, PCzOPOCz with carbazole moiety gave better performances due to balance of carrier flux from carbazole moiety with good hole transport ability. [ABSTRACT FROM AUTHOR]

Sulfur quantum dots (SQDs) represent a new class of luminescent nanomaterials. They have shown great potential in numerous application fields including sensing, cell imaging, photocatalysis, light emitting diodes and polymer nanocomposites, due to their unique composition, favorable optical properties, low toxicity, fine processability and low cost. This Minireview summarizes the recent research progress on the synthesis, characterization, properties and applications of SQDs, especially those synthesized from elemental sulfur. Critical yet unsolved issues in the synthesis and applications of SQDs are also discussed. In addition, an outlook for future research trends of SQDs is presented. [ABSTRACT FROM AUTHOR]

Polymer films based on poly vinyl alcohol (PVA) doped with different contents (0, 4, 8, 16, 20 and 28) wt% of Erbium(III) ions were synthesized by the simple solution casting technique. The structural characteristics of the films were studied by X-ray diffraction pattern (XRD), Fourier transform infrared (FT-IR) spectroscopy and atomic force microscopy measurements (AFM) measurement whereas the optical behavior of these films have been investigated using UV–Vis-NIR spectroscopy and photoluminescence measurements. The structural parameters of the interplanar (d) spacing, crystallite length (L) and the average interchain separation determined from the XRD and the absorption bands of the active IR groups recorded in FT-IR spectra indicate bonding of positively charged Er3+ ions with negatively charged OH groups of the PVA chains. The average cluster size (D) of the samples estimated from AFM data shows larger values than that obtained from XRD measurements. The optical gaps obtained from absorption spectra fitting and Tauch relations are approximately equal and slightly decreased by Er3+ ions incorporation in the PVA matrix whereas the high frequency refractive indices estimated according to Moss and Dimitrov formulae showing small increase. Three intense peaks of 607 nm, 733 nm and 783 nm wavelengths due to energy levels transitions of erbium were recorded in the photoluminescence spectra PVA–Er3+. The collected data support consideration of PVA–Er3+ films as a promising optical polymer material in microptics, planar polymer waveguides, polymer optical fiber and polymer light emitting diodes applications. [ABSTRACT FROM AUTHOR]

Limited charge carrier mobility of organic semiconductors, especially for solution‐processed polymer thin films, has typically relegated organic electronics to low‐frequency operation. Nevertheless, thanks to a steady increase in electronic properties of organics, much higher operation frequencies are feasible, suggesting a possible and appealing scenario where lightweight, cost‐effective, and conformable electronics can integrate both sensing and radio‐frequency transmitting functionalities, which are the key to unlock pervasive networks of distributed sensors revolutionizing human–environment interaction. Few years ago, it was suggested that gigahertz (GHz) field‐effect transistors could be achievable even with solution‐based processes. This was the basis for the European Research Council project high‐frequency printed and direct‐written organic‐hybrid integrated circuits (HEROIC), which in the last few years investigated such unexplored path. Here, the authors report their vision toward the achievement of radio‐frequency organic electronics mainly with solution‐based and scalable processes, with reference to the experience of the HEROIC project and to some of the most notable literature examples. The authors show that the achievement of solution‐processable organic field‐effect transistors with GHz operation is indeed feasible, but requires considering a carefully revised scenario in which the main role is played by charge injection, together with the geometric overlap, the capacitive parasitism associated to fringing and some constraints on the dielectric layer thickness. [ABSTRACT FROM AUTHOR]

The charge transport and recombination in light‐emitting diodes (LEDs) based on a methyl‐substituted poly(p‐phenylene) ladder polymer (Me‐LPPP) are investigated. The transport is characterized by a high room‐temperature hole mobility of 2 × 10−8 m2 V−1 s−1 combined with anomalously strong electron trapping. Their electroluminescence (EL) spectrum is characterized by a blue singlet emission, a broad green featureless peak, and a yellow‐orange triplet emission. The voltage dependence of the EL spectrum and negative contribution to the capacitance indicate that the triplet‐emission is of trap‐assisted nature, consistent with the strong electron trapping. Consequently, the color purity of the blue emissive Me‐LPPP polymer LEDs can be strongly improved using trap dilution. [ABSTRACT FROM AUTHOR]

The article focuses on the Polycyclic heavy hydrocarbons (HHs) such as coal, tar, and pitch are a family of materials with extremely rich and complex chemistry, representing a massive opportunity for their use in a range of potential applications; and mentions that optimal selection of initial HHs based on molecular constituents is essential in tuning the material for a particular and targeted electronic application.

Neither of us can remember people talking about stimuli‐responsive polymers when we were students. Even though this was still in the last century, it was almost 70 years after Staudinger's seminal paper "Über Polymerisation"![1] By the time we entered graduate school in the early 1990 s, the first papers on polymer light emitting diodes appeared, while research on electrically conducting, nonlinear optical, and other "functional" polymers was already in full swing. Looking back, there were some stimuli‐responsive materials that were around at the time,[2–6] but it took the better part of the last 30 years until the field had developed into what we think is one of the most vibrant areas of polymer science.[8–12] Before the potential usefulness of this class of materials was recognized, researchers were focused on developing polymeric materials that would not respond to external influences, and in fact maintain (in particular) their mechanical properties in a wide range of environments. This has led to the development of many environmentally robust polymers, which have come to impact basically every aspect of our daily life. Ironically, this long‐sought stability now comes back to haunt us in the form of plastic pollution, but this is another story. The concept of materials that adapt their properties in response to changing environmental conditions might appear like a complete reversal with respect to the original goals of creating stable materials. However, eventually a) it was recognized that materials that respond to a specific stimulus in a predictable and useful manner would significantly broaden the potential usefulness of polymers, and b) the field of polymer science had developed to the point where the rational design, preparation, and characterization of such materials became possible. The expression 'stimuli‐responsive polymer' had been first used in the 1980's, however its use really only gained popularity a few decades later. In the early days, terms such as environmentally‐sensitive or environmentally‐responsive polymers, stimuli‐reversible or stimuli‐sensitive polymers, or polymers with phase transitions have also been used. [ABSTRACT FROM AUTHOR]

A flexible, self-powered and semi-transparent mid-infrared photodetector is demonstrated with graphene and poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT: PSS) composite on poly vinyl alcohol (PVA) substrate. The effective dispersion of graphene nanoplatelets within polymer chains has yielded a low requisite loading of graphene – only 3 wt% for the implement of a detector with optimized photo-thermoelectric effect, high flexibility and high transparency. Under a broadband infrared radiation with peak wavelength at 7.8 μm, 1.4 × 107 cm Hz1/2 W−1 photo detectivity is achieved in composite detector, which is 22 times higher than pure PEDOT: PSS. The demonstrated detector array exhibits good optical transparency of 63% and is capable of being bent to a radius of 1 mm due to strong interaction between composite film and PVA substrate. These features make this scalable mid-infrared photodetector very promising as next-generation optoelectronics. Image 1 [ABSTRACT FROM AUTHOR]

Information about the outermost atomic layer of a material is critically important for many processes and materials, including in catalysis, tribology, wetting, corrosion, and thin film growth. Low energy ion scattering (LEIS) is an extremely surface sensitive technique that can quantitatively analyze the outermost atomic layer of a material. Recent developments in LEIS have resulted in a particularly high sensitivity version of the technique known as high sensitivity LEIS (HS-LEIS). In LEIS and HS-LEIS, reference and/or standard materials allow straightforward quantitation of the spectra. In this submission, the authors show the HS-LEIS spectrum of a high purity calcium fluoride powder. CaF2 is a useful reference material for calcium in LEIS because it is relatively inexpensive, not hygroscopic, and available in high purity. Due to the applications/uses of calcium in different areas of science, including in catalysis, polymer light emitting diodes, organic photovoltaics, solid oxide fuel cells, and solar cells, these data may enable future work in these areas. A reference spectrum for gold is included with this submission. [ABSTRACT FROM AUTHOR]

Three novel conjugated polymers based on 9,9′‐dioctylfluorene unit and isoindolo[2,1‐a]benzimidazol‐11‐one with different fluorine substituents (0, 2 and 4) were synthesized. PLED and resistive memory devices based on these polymers were prepared consequently. PLED based on four‐fluorinated polymer showed the highest maximum brightness of 3192 cd m−2 with almost 5‐fold increase of current efficiency 8‐fold increase of external quantum efficiency compared to that of the other two, and all the PLEDs exhibited good emission stability with no noticeable change of electroluminescence even under high voltage of 10 V. The memory device of doubly‐fluorinated polymer exhibited ternary flash behavior with threshold voltages below −2.5 V, while device of four‐fluorinated polymer possessed ON/OFF current ratio above 104. Impact of fluorine substitutions on the performance of devices were briefly investigated. The results revealed that the improvement of device performance might not scale with the increasing number of fluorine substitutions, and the four‐fluorine‐substituted polymer and doubly‐fluorinated polymer could be encouraging materials for applications of PLED and resistive memory device and worth of further design of other new polymer systems. [ABSTRACT FROM AUTHOR]

In laser fault injection, an attacker injects laser to a chip implementing cryptography and exploits a fault to attack the cryptography. A promising approach to counteract fault injection attack is to detect an attempt of fault injection using sensors. In such a sensor-based countermeasure, a sensor detects a physical anomaly and raises an alarm so that the system can react to the attempt of an attack properly. Among them, the bit-flip detector, that detects a short-circuit current induced by a laser fault injection, is actively studied as an efficient realization. In this paper, we give the first security evaluation of the bit-flip detector. We show that an attacker can reveal an internal state by observing how the sensor reacts to laser fault injection. The leakage leads to a variant of probing attack that is feasible non-invasively. We also propose a new cryptanalytic technique that efficiently exploit the leakage to attack AES. [ABSTRACT FROM AUTHOR]

Over the past years, product designers have been involved in collaborative developments of smart material composites early on in the development process, to showcase creative applications of them. In these projects, the way the material is presented to the development team and the extent to which its properties are defined affect how designers understand the potentials and boundaries of the material and envision product applications. In the context of a European project, Light.Touch.Matters, we studied the attempt of designers to understand and prototype underdeveloped composites of thin-film organic light emitting diodes and piezoelectric polymer. Arguing for a collaborative exploration of the unique experiences that such underdeveloped composites unfold, we elaborate on a challenge designers face in understanding and prototyping the experiential qualities, specifically, the dynamic and performative qualities. The paper presents our design approach and complementary tools to overcome this challenge. It further discusses the applicability and limitations of the proposed design supports in the context of collaborative materials development and outlines future research directions. [ABSTRACT FROM AUTHOR]

• Designed and synthesized new 3 cyanopyridine based polymers for PLED applications. • Polymers display good light absorption as well as emission behavior. • Polymers possess wide band gap 2.59–2.80 eV with good thermal stability. • Their EL maxima range from 469 to 476 nm with blue emission in their PLED devices. In this work, we report the design of three new cyanopyridine scaffold based polymers, viz. TPy 1-3 as potential blue light emitters for PLED applications. The new polymer design comprise, a cyanopyridine core as an electron accepting entity, thiophene as an electron donating unit with different auxiliary donors, viz. phenylene (TPy 1), biphenyl (TPy 2), and fluorene (TPy 3), and have been synthesized, following standard synthetic protocols including Suzuki-cross coupling polymerization reaction. Further, in order to assess all the prerequisites to act as an active emitter, the polymers TPy 1-3, were subjected to structural, thermal, linear optical, electrochemical and computational studies. The results revealed that, all the polymers were thermally stable up to 300 ⁰C and their estimated optical band-gaps were found to be 2.59–2.80 eV. Finally, new polymer light emitting diode (PLED) were fabricated by employing the polymers TPy 1-3, as active emissive material with a configuration of ITO/PEDOT: PSS/Polymer/Al. Interestingly, all the fabricated devices, exhibited an intense blue electroluminescence at 12 V with low threshold voltages of 4.2–4.8 V, signifying an effective injection of electron in the device. [ABSTRACT FROM AUTHOR]

The degradation of polymer light-emitting diodes (PLEDs) under current stress is governed by the formation of hole traps. The presence of traps is reflected in the low-frequency response of PLEDs by a negative contribution to the capacitance that originates from trap-assisted recombination. Since the relaxation time scales with the (inverse) concentration of traps, impedance spectroscopy measurements allow for a quantitative determination of the amount of traps formed during degradation. We demonstrate that the obtained hole trap concentration is in agreement with the amount found by numerically modeling the increase in the PLED driving voltage. Impedance spectroscopy measurements are therefore useful as an in-situ characterization tool during PLED degradation, providing information on trap formation without numerical device modeling. [ABSTRACT FROM AUTHOR]

Highlights • Effect of blending MEH-PPV and BT on the electronic properties of the PLEDs has been investigated using Capacitance and Impedance Spectroscopy (IS) techniques. • Minimum parallel resistance (Rp) is obtained for PLEDs with MEH-PPV:BT blend ratio of 1:3. • Absence of negative capacitance in MEH-PPV:BT blend devices shows the suppression of trap-assisted non-radiative recombination. • Maximum conductance at small bias voltages is obtained for PLEDs with MEH-PPV:BT blend ratio of 1:3. • Blend of MEH-PPV:BT (1:3 ratio) is a good material combination for single layer PLEDs with enhanced charge transport. Abstract Light emitting polymer poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is blended with a wide bandgap electron transport material benzothiadiazole (BT) and its effect on the electronic properties has been studied by capacitance and impedance spectroscopy (IS) in PLEDs. The impedance data is fitted using equivalent circuit models and the minimum parallel resistance (Rp) at zero bias have been obtained for 1:3 ratio of MEH-PPV:BT blended devices. The negative capacitance (NC) shows the occurrence of the trap-assisted non-radiative recombination mechanism at low frequencies in the unblended MEH-PPV PLEDs. Further, this behavior is seen to be reduced in PLEDs with MEH-PPV:BT blends. This clearly suggests that the blending of MEH-PPV and BT at different weight ratios results in the suppression of trap-assisted recombination. This can be attributed to the elimination of trap states due to the dilution of semiconductor material on account of the addition of wide bandgap host material. Moreover, the blended devices have shown a significant improvement in the conductivity at small bias voltages. [ABSTRACT FROM AUTHOR]

Abstract Novel binuclear platinum complex (FPT) 2 Pt 2 (diPic) and mononuclear platinum complex (FPT)Pt(Pic) were designed and synthesized, where FPT is N-(4-(6-(9,9-diethyl-9H-fluoren-2-yl)pyridin-3-yl)phenyl) N-phenylbenzenamine, diPic is 3-(6-(2-carboxypyridin-3-yloxy)hexyloxy)picolinic acid, and Pic is picolinic acid. The photophysical, electrochemical and thermal properties, as well as electroluminescent (EL) properties for both platinum(II) complexes were studied. Compared to (FPT)Pt(Pic), (FPT) 2 Pt 2 (diPic) exhibited stronger phosphorescent emission in PL spectra and higher Φ PL , owing to the enhanced spin-orbit interaction of platinum centers. Moreover, the monochromatic devices based on (FPT) 2 Pt 2 (diPic) showed better EL properties than (FPT)Pt(Pic). Based on that, the single-emissive-layer WPLEDs using (FPT) 2 Pt 2 (diPic) as orange emitter and FIrpic as blue emitter were also obtained. The WPLEDs show best performances with a maximal LE of 1.3 cd/A, and a CIE coordinates of (0.35, 0.37) which is very close to the pure white emission. Work is still underway to improve the device efficiency and color purity of these iridium and platinum complexes co-doped WPLEDs. Graphical abstract A novel binuclear platinum complex (FPT) 2 Pt 2 (diPic) is designed and synthesized. Both orange and white PLEDs are fabricated with a simple single-emission-layer configuration based on (FPT) 2 Pt 2 (diPic). The WPLEDs combination of (FPT) 2 Pt 2 (diPic) with FIrPic exhibit a CIE coordinates of (0.35, 0.37), which is very close to the pure white color. Image 1 Highlights • Novel binuclear platinum complex and mononuclear platinum complex were synthesized. • Photophysical, electrochemical and thermal properties of Pt complexes were studied. • (FPT) 2 Pt 2 (diPic) exhibited stronger phosphorescent emission and higher Φ PL. • The monochromatic devices based on (FPT) 2 Pt 2 (diPic) show better EL property. • The single-emissive-layer WPLEDs based on (FPT) 2 Pt 2 (diPic) and FIrpic were achieved. [ABSTRACT FROM AUTHOR]

We have designed and synthesized two novel yellow phosphorescent iridium complexes using dibenzothiophene-S,S-dioxide-based cyclometalated ligand for the first time, which are capable of producing highly efficient yellow and white polymer light-emitting devices (PLEDs). The resulted iridium complexes display good thermal stability and high photoluminescence quantum yields. Both yellow and white PLEDs are fabricated with an identical single-emission-layer configuration of ITO/PEDOT:PSS/emission layer (EML)/CsF/Al. For the yellow phosphorescent PLEDs based on ( p -CzFSOPy) 2 IrPic, the best device performances with a peak luminous efficiency (LE) of 13.3 cd/A and a peak external quantum efficiency (EQE) of 5.3% are achieved. More importantly, the two-element WPLEDs containing iridium (III)bis (2-(4,6-difluorophenyl)-pyridinato-N,C 2′ ) picolinate (FIrpic) as blue and ( p -CzFSOPy) 2 IrPic as yellow phosphors doped into a PVK:OXD- 7 matrix at an appropriate ratio exhibited a maximum LE of 19.2 cd/A, a maximum EQE of 9.6%, an extremely high luminance of 18717 cd/m 2 and Commission Internationale de L'Eclairage (CIE) coordinate of (0.317, 0.448). Moreover, at a luminance for practical application of 1000 cd/m 2 , the LE still remains as high as 19.0 cd/A, with a very slight decrease. [ABSTRACT FROM AUTHOR]

Palladium catalyzed Stille coupling reactions are extensively used for the preparation of functionalised thiophene based polymers. In addition, polycondensation via direct C-H arylation produces alternating copolymers in moderate yields. In the present work, we report the synthesis and optoelectronic properties of thiophene based compounds having rigid cycloalkanone and a novel hexhydro-2 H -indazole spacers in between. X-ray diffraction analysis shows the semi-crystalline nature of the synthesized materials with extensive side chain crystallinity. Band-gap energy of the synthesized materials has been obtained experimentally via optical and electrochemical methods and theoretically via computational studies. Open aperture Z-Scan results confirm the competence of these materials as optical limiters (NLO) while the photoluminescence emission characteristics and Schottky diode characteristics indicate their application prospects in Polymer Light Emitting Diodes (PLEDs). Polymers having hexhydro-2 H -indazole spacers appear to be promising candidates for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Abstract Through free-radical copolymerization of the Yb3+-centered near-infrared (NIR) luminescent complex monomer [Zn(L1)(4-vinyl-Py)Yb(L2) 3 ] (2) (H 2 L1 = N,N'-bis(salicylidene)−1,2-diamine; 4-vinyl-Py = 4-vinyl-pyridine and HL2 = (Z)−3-methyl-1-phenyl-4-(2,2,2-trifluoro-1-hydroxyethylidene)−1 H -pyrazol-5(4 H)-one) with NVK (N-vinylcarbazole), the obtained [Zn(L1)(4-vinyl-Py)Yb(L2) 3 ]-grafted polymer Poly(NVK- co -2) with additional PVK (Poly(N -vinylcarbazole)) to Yb3+ ion Föster energy transfer is used as the emitting material of polymer light-emitting diode (PLED), exhibiting the Yb3+-centered NIR outputs at 980 nm with a maximum efficiency of 0.049% (at 5.62 mA/cm2) and a maximum irradiance of 78.68 μ W/cm2 (at 16 V), respectively. This superior performance to those of previously reported organo-Yb3+-doped polymer systems, together with the characters of low turn-on voltage of 7 V and weak efficiency-roll-off (0.049–0.031% upon 5.62–233.6 mA/cm2), indicates that organo-Yb3+-grafted polymer is an effective strategy to develop PLEDs with the wavelength extended to 980 nm. Graphical abstract Based on [Zn(L1)(4-vinyl-Py)Yb(L2) 3 ] (2)-grafted polymer Poly(NVK- co -2) , Yb3+-centered NIR PLED with record-renewed performance (a maximum efficiency of 0.049%, a maximum irradiance of 78.68 μ W/cm2), low turn-on voltage of 7 V and weak efficiency-roll-off is realized. fx1 Highlights • Organo-Yb3+-complex-grafted PVK with ideal physical properties is obtained. • PLED based on organo-Yb3+-complex-grafted PVK is realized. • The device's superior performance (Yb3+-centered NIR outputs at 980 nm; maximum efficiency of 0.049%; maximum irradiance of 78.68 μ W/cm2; low turn-on voltage of 7 V and weak efficiency-roll-off) is approached. [ABSTRACT FROM AUTHOR]

[Display omitted] • The triphenylamine based two different π-conjugated heterocyclic polymers were prepared by Suzuki-coupling reaction. • The blue, red, and white emission obtained with the luminance of 6326, 4256, and 4596 cdm−2. • The novel method to achieve white light emission by simple method for the PLED manufacturing technology. The fine tuning of color and white light emission was achieved from the simple blending of two different types of polychromophores. The π-conjugated polymeric chromophores (blue and red) were synthesized and characterized for white light polymer emitting diode (WPLED) applications. The binary luminescent materials, Blue polymeric chromophore (BPy) and (Red polymeric chromophore (RPy), were obtained from the respective monomers via a standard Suzuki coupling reaction. The tuning of colors and white light emission were attained directly mixing of two polymeric chromophores (blue, red) in different ratio. The prepared polymer materials were confirmed using standard tehniques such as, Fourier transform infrared (FT-IR) and 13C and 1H-nuclear magnetic resonance (NMR) spectroscopy, while the gel-permeation chromatography result revealed the polymeric properties of the materials. The polymeric materials surfaces morphologies were analysed throught the FE-SEM and AFM analysis. The TGA (Thermogravymetric analysis) used to study the thermal property of the two prepared polymeric materials. The UV–visible and fluorescence spectrophotometry was applied to examine the optical features of the materials. The BPy and RPy polymers shows absorption peaks at 375 nm and 426 nm, respectively. The obatined emission peaks of BPy and RPy are at 426 nm and 603 nm, respectively. These results show that BPy and RPy belong to the blue and red emissive categories, and the white light emission was obtained with the mixing ratio of BPy(80%)-RPy(20%). The bandgap of these materials was calculated by cyclic voltammetry, and the theoretical bandgap of the materials was calculated by density functional theory analysis. Finely structured devices were fabricated, and the efficiencies of the BPy, RPy, and BPy-RPy were analyzed to assess the luminance productivity of the materials. In summary, this paper proposes a simple method to achieve white color emission by mixing polymeric chromophores at different ratios. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel design strategy with controllable steric hindrance effect is proposed. • A novel polymer platform with simple polymerization conditions is proposed. • The influencing mechanism of Linker units on the photoelectric properties was investigated. • Non-conjugated blue TSCT polymers with high EQE up to 23.2 % has been prepared. The exploration of blue polymeric emitters plays an important role in the application of solution-processed polymer light-emitting diodes (PLEDs) in full color display. But the development of highly efficient blue thermally activated delayed fluorescence (TADF) polymers is still extremely challenging. Here, a series of rigid non-conjugated polyimide (PI)-based blue thermally activated delayed fluorescence (TADF) polymers with through-space charge transfer effect were firstly reported based on our novel design strategy. Among them, TRZ- o C-ph (λ em = 497 nm) with a typical face-to-face structure as TADF unit was introduced into a polyimide backbone using twisted alicyclic imide as Linker unit. The twisted Linker unit with different structures can effectively regulate the d-spacing between donor and acceptor in the TADF unit, thus obtaining a series of blue TADF polyimides with λ em at 485 nm, and high thermal stability (T g > 277 °C, T d > 477 °C). Remarkably, highly-efficient solution-processing blue polymer light emitting diodes (PLEDs) based on the above polyimides were successfully assembled, with a maximal external quantum efficiency of 23.2%. Such outstanding efficiency is amongst the state-of-the-art performance of non-conjugated PLEDs. It confirms the effectiveness of the structural design strategy, and provides useful and valuable guidance for the development of highly-efficient blue TADF polymer materials and PLEDs. [ABSTRACT FROM AUTHOR]

Polymer Light Emitting Diodes (PLEDs), the most promising name in the field of display technology has received tremendous attention from various research groups. The research on light emitting polymers are an interdisciplinary zone which has challenging investigates on materials science and engineering, physics of device architecture and technology. This review addresses the wide range of tailored polymers, evolution of LED device structure for high performance, single and multicolor polymer based LEDs. Though, polymers are possessing better efficiency and easy fabrication processes, it has very low stability and short life. This study also reviews, device degradation during device fabrication and operation. [ABSTRACT FROM AUTHOR]

Abstract We investigate the possible triplet-triplet annihilation (TTA) process involving the conversion of triplet to singlet excitons by measuring the magnetoconductance (MC) and magnetoelectroluminescence (MEL) responses of the phenyl-substituted poly(p -phenylene vinylene) copolymer (super yellow, SY-PPV)-based polymer light-emitting diodes (PLEDs). Under low applied magnetic field (< 200 Oe), both the positive MC and MEL are observed. However, at high magnetic field (> 200 Oe), the magnitude of MEL decreases as a consequence of the decreased TTA process of triplet to singlet excitons and the fluorescence. We increase the concentration and lifetime of the triplet excitons by biasing SY-PPV-based PLEDs at the high current density and in the low temperature regime, respectively, to verify the TTA process. We observe an evident drop in MEL magnitude at 1000 Oe for the device constantly biased with 166.67 mA/cm2 at 100 K, which is correlated with the reduced TTA process under the high magnetic field. The TTA process may harvest the energy from triplet to singlet excitons in SY-PPY active layer and in part contribute the emission to fluorescence in PLEDs especially in the high current density regime. Graphical abstract Image 1 Highlights • The magnitude of MEL decreases as a consequence of the decreased TTA process of triplet to singlet excitons. • Biasing SY-PPV-based PLEDs at the high current density and in the low temperature regime increases TTA process. • TTA process harvests the energy from triplet to singlet excitons in SY-PPY active layer and in part contributes the emission to fluorescence in PLEDs. [ABSTRACT FROM AUTHOR]

Inverted polymer light emitting diodes (PLEDs), where solution-processed multi-layers were sandwiched between indium tin oxide and thermally evaporated aluminum electrodes, were fabricated and their characteristics were measured. In order to achieve high performance in the inverted PLEDs, there is a need for additional functional layers such as a hole transport layer and hole injection layer (HIL) on an emission layer (EML), but formation of the solution-processed layers on the hydrophobic EML have been rarely reported due to the extremely poor wetting property of a poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) solution, which is a widely used HIL. Non-wetting phenomena such as the formation of islands or radiation patterns in PEDOT:PSS films on the EML caused by their poor wetting property have been completely removed using a dilution method. By diluting PEDOT:PSS solutions with ethanol and analyzing a wetting envelope, we found the optimized dilution condition (10:1) and fabricated highly efficient inverted PLEDs with the uniformly coated PEDOT:PSS HIL, showing a current efficiency of 9.73 cd/A at 1000 cd/m 2 and uniform light emission simultaneously. [ABSTRACT FROM AUTHOR]

Abstract Co x Zn 1-x O (x = 0.01, 0.05 and 0.1) nanoparticles were prepared by microwave-assisted polyol method from zinc acetate dihydrate and Co(II) acetylacetonate. The reactions were performed in diethylene glycol (DEG) at 250 °C with the use of oleic acid as a surfactant. Resulting nanoparticle (ca. 10 nm) precipitates were washed with methanol and dried or kept as colloidal solutions redispersed in toluene. Colloidal solutions were mixed with the Poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) polymer to produce thin nanocomposite layers with specific optoelectronic properties. The electronic structure in terms of density of states (DOS) of MEH-PPV and MEH-PPV/nanocomposite layers was investigated by recently proposed energy resolved electrochemical impedance spectroscopy method. The MEH-PPV polymer and its nanocomposites with ZnO or Co x Zn 1-x O nanoparticles were used as thin active layers in polymer light emitting diodes (PLED). The nanocomposite layers exhibited optoelectronic properties which were found to be beneficial as the active layer in PLEDs, exhibiting an order of magnitude enhancement in electroluminescence intensity. A pronounced effect on the opening bias voltage of final devices with Co x Zn 1-x O nanoparticles was also observed. Graphical abstract Image 1 Highlights • Original facile microwave-assisted synthesis of Co x Zn 1-x O nanocolloids is reported. • Solution of MEH-PPV polymer and Co x Zn 1-x O nanodispersions mix without precipitation. • MEH-PPV/Co x Zn 1-x O composite layers electronic structure mapping by ER-EIS technique. • PLEDs with MEH-PPV/Co x Zn 1-x O nanocomposite active layer were successfully prepared. • The PLEDs with MEH-PPV/Co x Zn 1-x O layer exhibited lowering of opening bias voltage. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Original facile microwave-assisted synthesis of Zinc oxide nanoparticles is reported. • Prepared ZnO nanoparticles form stable colloidal dispersions in toluene. • Solution of MEH-PPV polymer and ZnO nanodispersions mix without agglomeration. • Polymer LEDs with MEH-PPV/ZnO nanocomposite active layer were successfully prepared. • The PLEDs with MEH-PPV/ZnO layer exhibited high electroluminescence at low voltage. Abstract Zinc oxide nanoparticles were synthesized via microwave-assisted reactions from a zinc acetate dihydrate. The reactions were performed in diethylene glycol (DEG) at 220 °C and 250 °C while using oleic acid as the surfactant. The ZnO precipitates obtained were washed with methanol and dried or kept as colloidal solutions redispersed in toluene. The size of the nanoparticles ranged from ca. 5 to 12 nm and they could be modified by the concentration of Zn precursor. Different morphologies due to the function of oleic acid concentration were observed. The resulting ZnO nanocolloids were mixed with the poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) polymer to obtain MEH-PPV/ZnO nanocomposites. The nanocomposite layers exhibited optoelectronic properties which were found to be beneficial for being applied as the active layer in the polymer light emitting diodes. The intensity of the electroluminescence of the prepared PLED devices was enhanced by one order of magnitude keeping all other parameters constant and powered as the same operation voltage. As additional step the effect of active layer thickness on optoelectronic performance of PLED devices was investigated as well. [ABSTRACT FROM AUTHOR]

We have investigated the effect of blending electron deficient heterocycle Benzothiadiazole (BT) on the photo-physical properties of conjugated polymer Poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). Quantum yield (QY) value has been found to increase from 37% for pure MEH-PPV to 45% for an optimum MEH-PPV:BT blend ratio of 1:3. This can be attributed to the efficient energy transfer from the wide bandgap BT (host) to the small bandgap MEH-PPV (guest). The FTIR spectrum of MEH-PPV:BT blended thin film indicates suppression of aromatic C-H out-of-plane and in-plane bending, suggesting planarization of the conjugated polymer chains and, hence, leading to increase in the conjugation length. The increase in conjugation length is also evident from the red-shifted PL spectra of MEH-PPV:BT blended films. Single layer MEH-PPV:BT device shows lower turn-on voltage than single layer MEH-PPV alone device. Further, the effect of electrical conductivity of PEDOT:PSS on the current-voltage characteristics is investigated in the PLED devices with MEH-PPV:BT blend as the active layer. PEDOT:PSS with higher conductivity as HIL reduces the turn on voltage from 4.5 V to 3.9 V and enhances the current density and optical output in the device. [ABSTRACT FROM AUTHOR]

A novel iridium complex grafting hole-transporting triphenylamine (TPA) unit onto cyclometalated ligand, namely t-BuPyrPyTPA) 2 Ir(acac), was successfully synthesized and characterized. The photophysical, electrochemical and DFT/TD-DFT calculation, as well as electroluminescence properties of this iridium complex were fully investigated. Meanwhile, the PLEDs employing (t-BuPyrPyTPA) 2 Ir(acac) as dopant presented stable NIR emission peaked at 697 nm and a shoulder at 764 nm with a highest external quantum efficiency ( EQE ) of 0.56% at 4 wt% dopant concentration. These results demonstrate that expanding the conjugation length of the ligand is an effective way to achieve NIR emission. [ABSTRACT FROM AUTHOR]

Organic magnetic field effects (MFEs) have attracted a lot of interests in foundation research and practical applications. In this work, a thin layer of colloidal quantum dots QDs was incorporated into the planar heterojunction-based polymer light-emitting diodes (PLEDs) as a sensitizer to tune the organic MFEs. As a result, the magneto-electroluminescence (MEL) and magneto-conductance (MC) in the poly [2-(4-(3′,7′-dimethyloctyloxyphenyl)-1,4-phenylene vinylene)] (P-PPV)-based PLEDs can be tuned synchronously from positive to negative. The current and temperature dependences of the negative MEL and MC were studied elaborately, showing normal and anomalous dependences compared to those of typical positive MEL and MC, respectively. The underlying mechanism of negative MEL and MC was examined. It is revealed that efficient Förster energy transfer between P-PPV and QDs is responsible for the effective tuning of MEL and MC via promoting the reverse intersystem crossing between electron-hole pairs. [ABSTRACT FROM AUTHOR]

Semi-orthogonal solution processing can circumvent interface intermixing issue of construction of multilayer polymer light-emitting diode devices (PLEDs). In this manuscript, we developed a new strategy to construct multilayer PLEDs by the semi-orthogonal solvents based on the difference between the solubilities of a poly(9,9-dioctylfluorene) that end-capped with a triphenylamine derivative (PFO-TF) (processed with p -xylene) and the light-emitting polymer PPF-SO15 or PPF-SO15-BT1 (processed with 1,4-dioxane). As the highest occupied molecular orbital energy level of PFO-TF (−5.70 eV) lies in between PEDOT:PSS (−5.20 eV) and the light-emitting copolymer PPF-SO15 (−5.94 eV), it can serve as the hole transport layer (HTL) to facilitate hole injection. The blue PLED based on PFO-TF as the HTL exhibits lower turn-on voltage and nearly identical electroluminescent spectra as that of the control device without HTL. Of particular importance is that the blue device with PFO-TF as the HTL exhibits the luminous efficiency over 5.0 cd A −1 , which is much higher than that observed from a device without an HTL (3.51 cd A −1 ) or one with traditional poly(9-vinylcarbazole) as the HTL (4.74 cd A −1 ). Similar trend is also realized for PLEDs based on green-light-emitting polymer PPF-SO15-BT1. These observations indicate that processing of a multilayer device with this specific semi-orthogonal system may be a promising strategy for the construction of efficient PLEDs. [ABSTRACT FROM AUTHOR]

Transition metal oxides are being more frequently used as hole injection layer (HIL) in organic light emitting diodes (OLEDs), in place of polymer HILs such as PEDOT:PSS. The very thin films of the metal oxide HILs are usually deposited using vapor deposition, in order to create uniform films. Here, we report OLEDs fabricated using solution processed MoO x films as the HIL and super yellow as the emissive layer. The performance of the devices is comparable to PEDOT:PSS based devices, while the stability tests show the lifetime of MoO x -based devices is 4 × 10 6 h, about 40 times longer than PEDOT:PSS devices, at typical working condition. X-ray photoelectron spectroscopy (XPS) indicates both Mo 5+ and Mo 6+ states in the film. The Oxygen vacant MoO 3 film shows bandgap states close to valence band, as confirmed by ultraviolet photoelectron spectroscopy and optical absorption. The method show promise for all-solution- processed LEDs utilizing metal oxide HILs. [ABSTRACT FROM AUTHOR]