NEXAFS spectroscopy of alkylated benzothienobenzothiophene thin films at the carbon and sulfur K-edges.

Alkylated benzothienobenzothiophenes are an important class of organic semiconductors that exhibit high performance in solution-processed organic field-effect transistors. In this work, we study the near-edge x-ray absorption fine-structure (NEXAFS) spectra of 2,7-didecyl[1]benzothieno[3,2-b][1]benzothiophene (C10-BTBT) at both the carbon and sulfur K-edges. Angle-resolved experiments of thin films are performed to characterize the dichroism associated with molecular orientation.

A New Organic Laser Material Design Toward Ultra-Low Amplified Spontaneous Red Emission and Ultra-Bright Electroluminescence.

Significant efforts are dedicated to developing new classes of organic semiconductor materials to achieve electrically pumped lasing. However, further advancements are necessary to understand the relationship between the structure and property for the creation of innovative laser materials with high stability, low triplet yield, ultra-low lasing threshold, and low-efficiency roll-off at ultra-bright electroluminescence. Here, a new design principle is validated for organic semiconductor laser materials, demonstrating simultaneous enhancement in the key figures of merit of low amplified spontaneous emission thresholds (E), efficient electroluminescence, and low triplet yields.

End Cap Effect on Solution-Processable Deep Blue Lasing Materials with Low-Amplified Spontaneous Emission Thresholds.

Organic lasers have attracted increasing attention owing to their superior characteristics such as lightweight, low-cost manufacturing, high mechanical flexibility, and high emission-wavelength tunability. Recent breakthroughs include electrically pumped organic laser diodes and an electrically driven organic laser, integrated with an organic light-emitting diode pumping. However, the availability of efficient deep blue organic laser chromophores remains limited.

Blue emitting exciplex for yellow and white organic light-emitting diodes.

White organic light-emitting diodes (WOLEDs) have several desirable features, but their commercialization is hindered by the poor stability of blue light emitters and high production costs due to complicated device structures. Herein, we investigate a standard blue emitting hole transporting material (HTM) N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) and its exciplex emission upon combining with a suitable electron transporting material (ETM), 3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ). Blue and yellow OLEDs with simple device structures are developed by using a blend layer, NPB:TAZ, as a blue emitter as well as a host for yellow phosphorescent dopant iridium (III) bis(4-phenylthieno[3,2-c]pyridinato-N,C)acetylacetonate (PO-01).

Accelerated Redox Reactions Enable Stable Tin-Lead Mixed Perovskite Solar Cells.

The facile oxidation of Sn to Sn poses an inherent challenge that limits the efficiency and stability of tin-lead mixed (Sn-Pb) perovskite solar cells (PSCs) and all-perovskite tandem devices. In this work, we discover the sustainable redox reactions enabling self-healing Sn-Pb perovskites, where their intractable oxidation degradation can be recovered to their original state under light soaking. Quantitative and operando spectroscopies are used to investigate the redox chemistry, revealing that metallic Pb from the photolysis of perovskite reacts with Sn to regenerate Pb and Sn spontaneously.

Large area inkjet-printed OLED fabrication with solution-processed TADF ink.

This work demonstrates successful large area inkjet printing of a thermally activated delayed fluorescence (TADF) material as the emitting layer of organic light-emitting diodes (OLEDs). TADF materials enable efficient light emission without relying on heavy metals such as platinum or iridium. However, low-cost manufacturing of large-scale TADF OLEDs has been restricted due to their incompatibility with solution processing techniques.

Harvesting Triplet Excitons in High Mobility Emissive Organic Semiconductor for Efficiency Enhancement of Light-Emitting Transistors.

Organic light-emitting transistors (OLETs), a kind of highly integrated and minimized optoelectronic device, demonstrate great potential applications in various fields. The construction of high-performance OLETs requires the integration of high charge carrier mobility, strong emission, and high triplet exciton utilization efficiency in the active layer. However, it remains a significant long-term challenge, especially for single component active layer OLETs.

Amplified Spontaneous Emission from Zwitterionic Excited-State Intramolecular Proton Transfer.

The unique four-level photocycle characteristics of excited-state intramolecular proton transfer (ESIPT) materials enable population inversion and large spectral separation between absorption and emission through their respective enol and keto forms. This leads to minimal or no self-absorption losses, a favorable feature in acting as an optical gain medium. While conventional ESIPT materials with an enol-keto tautomerism process are widely known, zwitterionic ESIPT materials, particularly those with high photoluminescence, are scarce.

Cibalackrot Dendrimers for Hyperfluorescent Organic Light-Emitting Diodes.

Hyperfluorescent organic light-emitting diodes (HF-OLEDs) enable a cascading Förster resonance energy transfer (FRET) from a suitable thermally activated delayed fluorescent (TADF) assistant host to a fluorescent end-emitter to give efficient OLEDs with relatively narrowed electroluminescence compared to TADF-OLEDs. Efficient HF-OLEDs require optimal FRET with minimum triplet diffusion via Dexter-type energy transfer (DET) from the TADF assistant host to the fluorescent end-emitter. To hinder DET, steric protection of the end-emitters has been proposed to disrupt triplet energy transfer.

Low Light Amplification Threshold and Reduced Efficiency Roll-Off in Thick Emissive Layer OLEDs from a Diketopyrrolopyrrole Derivative.

External quantum efficiency (EQE) roll-off under high current injection has been one of the major limiting factors toward the development of organic semiconductor laser diodes (OSLDs). While significant progress in this regard has been made on organic semiconductors (OSCs) emitting in the blue-green region of the visible spectrum, OSCs with longer wavelength emission (>600 nm) have fallen behind in both material development and the advancement in device architectures suitable for the realization of OSLDs. Therefore, to make simultaneous incremental advancements, a host-guest system comprising of a high performing poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) polymer and an efficient small molecule laser dye, dithiophenyl diketopyrrolopyrrole (DT-DPP), is used.

Probing polaron-induced exciton quenching in TADF based organic light-emitting diodes.

Polaron-induced exciton quenching in thermally activated delayed fluorescence (TADF)-based organic light-emitting diodes (OLEDs) can lead to external quantum efficiency (EQE) roll-off and device degradation. In this study, singlet-polaron annihilation (SPA) and triplet-polaron annihilation (TPA) were investigated under steady-state conditions and their relative contributions to EQE roll-off were quantified, using experimentally obtained parameters. It is observed that both TPA and SPA can lead to efficiency roll-off in 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) doped OLEDs.

Liquid-phase sintering of lead halide perovskites and metal-organic framework glasses.

Lead halide perovskite (LHP) semiconductors show exceptional optoelectronic properties. Barriers for their applications, however, lie in their polymorphism, instability to polar solvents, phase segregation, and susceptibility to the leaching of lead ions. We report a family of scalable composites fabricated through liquid-phase sintering of LHPs and metal-organic framework glasses.

Application of Triplet-Triplet Annihilation Upconversion in Organic Optoelectronic Devices: Advances and Perspectives.

Organic semiconductor materials have been widely used in various optoelectronic devices due to their rich optical and/or electrical properties, which are highly related to their excited states. Therefore, how to manage and utilize the excited states in organic semiconductors is essential for the realization of high-performance optoelectronic devices. Triplet-triplet annihilation (TTA) upconversion is a unique process of converting two non-emissive triplet excitons to one singlet exciton with higher energy.

Tunable Light-Emission Properties of Solution-Processable N-Heterocyclic Carbene Cyclometalated Gold(III) Complexes for Organic Light-Emitting Diodes.

N-Heterocyclic carbene (NHC) cyclometalated gold(III) complexes remain very scarce and therefore their photophysical properties remain currently underexplored. Moreover, gold(III) complexes emitting in the blue region of the electromagnetic spectrum are rare. In this work, a series of four phosphorescent gold(III) complexes was investigated bearing four different NHC monocyclometalated (C^C*)-type ligands and a dianionic (N^N)-type ancillary ligand ((N^N)=5,5'-(propane-2,2-diyl)bis(3-(trifluoromethyl)-1 H-pyrazole) (mepzH )).

Solid cyclooctatetraene-based triplet quencher demonstrating excellent suppression of singlet-triplet annihilation in optical and electrical excitation.

Triplet excitons have been identified as the major obstacle to the realisation of organic laser diodes, as accumulation of triplet excitons leads to significant losses under continuous wave (CW) operation and/or electrical excitation. Here, we report the design and synthesis of a solid-state organic triplet quencher, as well as in-depth studies of its dispersion into a solution processable bis-stilbene-based laser dye. By blending the laser dye with 20 wt% of the quencher, negligible effects on the ASE thresholds, but a complete suppression of singlet-triplet annihilation (STA) and a 20-fold increase in excited-state photostability of the laser dye under CW excitation, were achieved.

Charge and exciton dynamics of OLEDs under high voltage nanosecond pulse: towards injection lasing.

Electrical pumping of organic semiconductor devices involves charge injection, transport, device on/off dynamics, exciton formation and annihilation processes. A comprehensive model analysing those entwined processes together is most helpful in determining the dominating loss pathways. In this paper, we report experimental and theoretical results of Super Yellow (Poly(p-phenylene vinylene) co-polymer) organic light emitting diodes operating at high current density under high voltage nanosecond pulses.

Mobility Evaluation of [1]Benzothieno[3,2- b][1]benzothiophene Derivatives: Limitation and Impact on Charge Transport.

Among contemporary semiconductors, many of the best performing materials are based on [1]benzothieno[3,2- b][1]benzothiophene (BTBT). Alkylated derivatives of these small molecules not only provide high hole mobilities but also can be easily processed by thermal vacuum or solution deposition methods. Over the last decade, numerous publications have investigated molecular structures and charge transport properties to elucidate what makes these molecules so special.

Hybrid Area-Emitting Transistors: Solution Processable and with High Aperture Ratios.

Area emission is realized in all-solution-processed hybrid light-emitting transistors (HLETs). A new HLET design is presented with increased aperture ratio, and optical and electrical characteristics are shown.

High-Performance, Fullerene-Free Organic Photodiodes Based on a Solution-Processable Indigo.

A solution-processable dibromoindigo with an alkyoxyphenyl solubilizing group is developed and used as a new electron acceptor in organic photodiodes. The solution-processed fullerene-free organic photodiodes show an almost spectrally flat response with a high responsivity (0.4 A W(-1)) and a high detectivity (1 × 10(12) Jones).

Defining the light emitting area for displays in the unipolar regime of highly efficient light emitting transistors.

Light-emitting field effect transistors (LEFETs) are an emerging class of multifunctional optoelectronic devices. It combines the light emitting function of an OLED with the switching function of a transistor in a single device architecture. The dual functionality of LEFETs has the potential applications in active matrix displays.

All solution-processed, hybrid light emitting field-effect transistors.

All solution-processed, high performance hybrid light emitting transistors (HLETs) are realized. Using a novel combination of device architecture and materials a bilayer device comprised of an inorganic and organic semiconducting layer is fabricated and the optoelectronic properties are presented.

Simultaneous enhancement of brightness, efficiency, and switching in RGB organic light emitting transistors.

An innovative design strategy for light emitting field effect transistors (LEFETs) to harvest higher luminance and switching is presented. The strategy uses a non-planar electrode geometry in tri-layer LEFETs for simultaneous enhancement of the key parameters of quantum efficiency, brightness, switching, and mobility across the RGB color gamut.

Ordered polymer nanofibers enhance output brightness in bilayer light-emitting field-effect transistors.

Polymer light emitting field effect transistors are a class of light emitting devices that reveal interesting device physics. Device performance can be directly correlated to the most fundamental polymer science. Control over surface properties of the transistor dielectric can dramatically change the polymer morphology, introducing ordered phase.

Control of efficiency, brightness, and recombination zone in light-emitting field effect transistors.

The split-gate light emitting field effect transistors (SG-LEFETs) demonstrate a new strategy for ambipolar LEFETs to achieve high brightness and efficiency simultaneously. The SG architecture forces largest quantity of opposite charges on Gate 1 and Gate 2 area to meet in the center of the channel. By actively and independently controlling current injection from separated gate electrodes within transporting channel, high brightness can be obtained in the largest injection current regime with highest efficiency.