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

UV/Ozone-Induced Interface Engineering for High-Performance Horizontal Organic Light-Emitting Transistors Operating at Low Voltage

Multifunctional organic light-emitting transistors (OLETs), which combine electric-switching and light-producing capabilities into a single device, are attracting increasing interest as promising candidates for new-generation display technology. Despite advancements in the design of organic luminescent materials and the optimization of device geometry configurations, maintaining operating voltage low while enhancing optical performances remains a key challenge in horizontally structured OLETs. Here, a simple and effective interfacial engineering strategy is employed to improve the optical properties of horizontal OLETs operating at low voltage, by introducing ultraviolet ozone (UVO)-induced surface modification on high-k dielectrics. It takes the role to not only control the surface activation states of dielectric layers but also optimize the growth dynamics behavior of channel film benefitting from the strong interfacial interaction between chemically modified dielectric surface and channel seed molecules. The optimized horizontal-channel OLET exhibits a significantly high brightness of 9,484 cd m- 2, more than 25 times greater than that of untreated OLETs (347 cd m- 2), along with a peak EQE of 9.64%, a low operating voltage of 15 V, and good dynamic gate stress stability, outperforming other reported horizontal-channel high-performance OLETs. This work demonstrates that dielectric/semiconductor interface engineering is essential for high-performance transistor-based optoelectronic devices including horizontal OLETs.

Conformation-Confined Organic Butterfly-Molecule with High Photoluminescence Efficiency, Deep-Blue Amplified Spontaneous Emission, and Unique Piezochromic Luminescence

Organic fluorophores with tunable π-conjugated paths have attracted considerable attention owing to their diverse properties and promising applications. Herein, we present a tailored butterfly-like molecule, 2,2'-(2,5-bis (2,2-diphenylvinyl)-1,4-phenylene)dinaphthalene (BDVPN), which exhibits diverse photophysical features in its two polymorphs. The BP phase crystal, with its "aligned wings" conformation, possesses emissive characteristics that are nearly identical to those in dilute solutions. In contrast, the BN phase crystal, which adopts an "orthogonal wings" conformation, exhibits an unusual hypsochromic-shifted emission compared to its dilute solution counterparts. This intriguing hypsochromic-shifted emission originates from the reduction in the effective conjugated length of the molecular skeleton. Notably, BN phase crystals also exhibit exceptional optical performance, featuring high-efficiency emission (76.6 %), low-loss optical waveguides (0.571 dB mm-1), deep-blue amplified spontaneous emission (ASE) with narrow full width at half maximum (FWHM: 6.4 nm), and a unique 200 nm bathochromic shift of piezochromic luminescence.

Recent advances in artificial neuromorphic applications based on perovskite composites

High-performance perovskite materials with excellent physical, electronic, and optical properties play a significant role in artificial neuromorphic devices. However, the development of perovskites in microelectronics is inevitably hindered by their intrinsic non-ideal properties, such as high defect density, environmental sensitivity, and toxicity. By leveraging materials engineering, integrating various materials with perovskites to leverage their mutual strengths presents great potential to enhance ion migration, energy level alignment, photoresponsivity, and surface passivation, thereby advancing optoelectronic and neuromorphic device development. This review initially provides an overview of perovskite materials across different dimensions, highlighting their physical properties and detailing their applications and metrics in two- and three-terminal devices. Subsequently, we comprehensively summarize the application of perovskites in combination with other materials, including organics, nanomaterials, oxides, ferroelectrics, and crystalline porous materials (CPMs), to develop advanced devices such as memristors, transistors, photodetectors, sensors, light-emitting diodes (LEDs), and artificial neuromorphic systems. Lastly, we outline the challenges and future research directions in synthesizing perovskite composites for neuromorphic devices. Through the review and analysis, we aim to broaden the utilization of perovskites and their composites in neuromorphic research, offering new insights and approaches for grasping the intricate physical working mechanisms and functionalities of perovskites.

Epitaxial Growth of Two-Dimensional Organic Crystals with In-Plane Heterostructured Domain Regulation

Complex organic lateral heterostructures (OLHs) with spatial distribution of two or more chemical components are crucial for designing and realizing unique structure-dependent optoelectronic applications. However, the precise design of well-defined OLHs with flexible domain regulation remains a considerable challenge. Herein, we present a stepwise solution self-assembly method to synthesize two-dimensional (2D) OLHs with a central rhombus domain and a lateral region featuring tunable blue and green emission based on the sequential nucleation and growth of 2D crystals. By controlling the initial crystallization time of 2,6-diphenylanthracene, the rhombic length ratio (α) of the multicolor-emissive part of the 2D OLHs is precisely modified. Furthermore, a third lateral layer is constructed on the resulting OLHs, demonstrating scalable lateral regulation. Significantly, these prepared 2D OLHs exhibit great excitation position-dependent waveguide characteristics and enable a 0.06 dB/μm low-loss waveguiding, which are conducive to photon transport and conversion for photonic integrated circuits. This work provides a stepwise strategy for the accurate fabrication of 2D OLHs, fabricating the developments of next-generation optoelectronics devices.

Single-crystalline hole-transporting layers for efficient and stable organic light-emitting devices

Efficient charge-carrier injection and transport in organic light-emitting devices (OLEDs) are essential to simultaneously achieving their high efficiency and long-term stability. However, the charge-transporting layers (CTLs) deposited by various vapor or solution processes are usually in amorphous forms, and their low charge-carrier mobilities, defect-induced high trap densities and inhomogeneous thickness with rough surface morphologies have been obstacles towards high-performance devices. Here, organic single-crystalline (SC) films were employed as the hole-transporting layers (HTLs) instead of the conventional amorphous films to fabricate highly efficient and stable OLEDs. The high-mobility and ultrasmooth morphology of the SC-HTLs facilitate superior interfacial characteristics of both HTL/electrode and HTL/emissive layer interfaces, resulting in a high Haacke's figure of merit (FoM) of the ultrathin top electrode and low series-resistance joule-heat loss ratio of the SC-OLEDs. Moreover, the thick and compact SC-HTL can function as a barrier layer against moisture and oxygen permeation. As a result, the SC-OLEDs show much improved efficiency and stability compared to the OLEDs based on amorphous or polycrystalline HTLs, suggesting a new strategy to developing advanced OLEDs with high efficiency and high stability.

Molecular phosphorescence enhancement by the plasmon field of metal nanoparticles

A theoretical model is proposed that allows the estimation of the quantum yield of phosphorescence of dye molecules in the vicinity of plasmonic nanoparticles. For this purpose, the rate constants of the radiative and nonradiative intramolecular transitions for rhodamine 123 (Rh123) and brominated rhodamine (Rh123-2Br) dyes have been calculated. The plasmon effect of Ag nanoparticles on various types of luminescence processes has been studied both theoretically and experimentally. We show that in the presence of a plasmonic nanoparticle, the efficiency of the immediate and delayed fluorescence increases significantly. The phosphorescence rate of the rhodamine dyes also increases near plasmonic nanoparticles. The long-lived luminescence i.e., delayed fluorescence and phosphorescence is more enhanced for Rh123-2Br than for Rh123. The largest phosphorescence quantum yield is obtained when the dye molecule is at a distance of 4-6 nm from the nanoparticle surface. Our results can be used in the design of plasmon-enhancing nanostructures for light-emitting media, organic light-emitting diodes, photovoltaic devices, and catalysts for activation of molecular oxygen.

A Domino Protocol toward High-performance Unsymmetrical Dibenzo[d,d']thieno[2,3-b;4,5-b']dithiophenes Semiconductors

Unsymmetric organic semiconductors have many advantages such as good solubility, rich intermolecular interactions for potential various optoelectronic applications. However, their synthesis is more challenging due to intricate structures thus normally suffering tedious synthesis. Herein, we report a trisulfur radical anion (S3⋅-) triggered domino thienannulation strategy for the synthesis of dibenzo[d,d']thieno[2,3-b;4,5-b']dithiophenes (DBTDTs) using readily available 1-halo-2-ethynylbenzenes as starting materials. This domino protocol features no metal catalyst and the formation of six C-S and one C-C bonds in a one-pot reaction. Mechanistic study revealed a unique domino radical anion pathway. Single crystal structure analysis of unsymmetric DBTDT shows that its unique unsymmetric structure endows rich and multiple weak S⋅⋅⋅S interactions between molecules, which enables the large intermolecular transfer integrals of 86 meV and efficient charge transport performance with a carrier mobility of 1.52 cm2 V-1 s-1. This study provides a facile and highly efficient synthetic strategy for more high-performance unsymmetric organic semiconductors.

High Mobility Emissive Excimer Organic Semiconductor Towards Color-Tunable Light-Emitting Transistors

Organic light-emitting transistors (OLETs) are highly integrated and minimized optoelectronic devices with significant potential superiority in smart displays and optical communications. To realize these various applications, it is urgently needed for color-tunable emission in OLETs, but remains a great challenge as a result of the difficulty for designing organic semiconductors simultaneously integrating high carrier mobility, strong solid-state emission, and the ability for potential tunable colors. Herein, a high mobility emissive excimer organic semiconductor, 2,7-di(2-anthryl)-9H-fluorene (2,7-DAF) was reasonably designed by introducing a rotatable carbon-carbon single bond connecting two anthracene groups at the 2,7-sites of fluorene, and the small torsion angles simultaneously guarantee effective conjugation and suppress fluorescence quenching. Indeed, the unique stable dimer arrangement and herringbone packing mode of 2,7-DAF single crystal enables its superior integrated optoelectronic properties with high carrier mobility of 2.16 cm2  ⋅ V-1  ⋅ s-1 , and strong excimer emission with absolute photoluminescence quantum yield (PLQY) of 47.4 %. Furthermore, the voltage-dependent electrically induced color-tunable emission from orange to blue was also demonstrated for an individual 2,7-DAF single crystal based OLETs for the first time. This work opens the door for a new class of high mobility emissive excimer organic semiconductors, and provides a good platform for the study of color-tunable OLETs.

A skeletal randomization strategy for high-performance quinoidal-aromatic polymers

Enhancing the solution-processability of conjugated polymers (CPs) without diminishing their thin-film crystallinity is crucial for optimizing charge transport in organic field-effect transistors (OFETs). However, this presents a classic "Goldilocks zone" dilemma, as conventional solubility-tuning methods for CPs typically yield an inverse correlation between solubility and crystallinity. To address this fundamental issue, a straightforward skeletal randomization strategy is implemented to construct a quinoid-donor conjugated polymer, PA4T-Ra, that contains para-azaquinodimethane (p-AQM) and oligothiophenes as repeat units. A systematic study is conducted to contrast its properties against polymer homologues constructed following conventional solubility-tuning strategies. An unusually concurrent improvement of solubility and crystallinity is realized in the random polymer PA4T-Ra, which shows moderate polymer chain aggregation, the highest crystallinity and the least lattice disorder. Consequently, PA4T-Ra-based OFETs, fabricated under ambient air conditions, deliver an excellent hole mobility of 3.11 cm2 V-1 s-1, which is about 30 times higher than that of the other homologues and ranks among the highest for quinoidal CPs. These findings debunk the prevalent assumption that a random polymer backbone sequence results in decreased crystallinity. The considerable advantages of the skeletal randomization strategy illuminate new possibilities for the control of polymer aggregation and future design of high-performance CPs, potentially accelerating the development and commercialization of organic electronics.

Nonvolatile Memory Organic Light-Emitting Transistors

In the field of active-matrix organic light emitting display (AMOLED), large-size and ultra-high-definition AMOLED applications have escalated the demand for the integration density of driver chips. However, as Moore's Law approaches the limit, the traditional technology of improving integration density that relies on scaling down device dimension is facing a huge challenge. Thus, developing a multifunctional and highly integrated device is a promising route for improving the integration density of pixel circuits. Here, a novel nonvolatile memory ferroelectric organic light-emitting transistor (Fe-OLET) device which integrates the switching capability, light-emitting capability and nonvolatile memory function into a single device is reported. The nonvolatile memory function of Fe-OLET is achieved through the remnant polarization property of ferroelectric polymer, enabling the device to maintain light emission at zero gate bias. The reliable nonvolatile memory operations are also demonstrated. The proof-of-concept device optimized through interfacial modification approach exhibits 20 times improved field-effect mobility and five times increased luminance. The integration of nonvolatile memory, switching and light-emitting capabilities within Fe-OLET provides a promising internal-storage-driving paradigm, thus creating a new pathway for deploying storage capacitor-free circuitry to improve the pixel aperture ratio and the integration density of circuits toward the on-chip advanced display applications.