以昇陳

Nature Materials, Published online: 06 April 2023; doi:10.1038/s41563-023-01529-w

We synthesized stretchable electroluminescent polymers capable of reaching a near-unity theoretical quantum yield through thermally activated delayed fluorescence. Their polymers show 125% stretchability with 10% external quantum efficiency and demonstrate a fully stretchable organic light-emitting diode.

Two thermally actived delayed fluorescence (TADF) materials with subtle chemical modification exhibit different luminescent behavior in aggregation state. Rigid X-aggregation maintains TADF emission with aggregation-induced emission (AIE) feature and efficient intramolecular intersystem crossing (ISC) and reverse ISC(RISC) process, whereas compact H-aggregation disables TADF emission channel with active intermolecular ISC, enhanced phosphorescence, and inhibited RISC process, which leads to aggregation-caused quenching (ACQ) character.

Abstract

The understanding of the excited state dynamics of thermally activated delayed fluorescence (TADF) materials is crucial. In this study, two donor–acceptor-type TADF emitters with highly twisted conformation are synthesized. The emitters with subtle chemical modification of donor unit exhibit opposite aggregation luminescent behaviors: aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ). Through the photophysical properties study, crystallographic analysis, and theory simulations, it is discovered that X-aggregation supports AIE behavior by restricting the intramolecular motions and preserving TADF emission via an efficient reverse intersystem crossing (RISC) process, but on the other hand, H-aggregation leads to ACQ behavior due to inhibited RISC, disabled TADF channel, and weak phosphorescence from radiative low-lying triplet state. The findings shed light on the excited-state dynamic behaviors of TADF emitters, which are dependent on aggregation.

Nature Photonics, Published online: 16 March 2023; doi:10.1038/s41566-023-01164-6

The addition of a strong coupling layer allows polariton-based emission from red and green organic light-emitting diodes with high external quantum efficiency up to 10%, linewidth smaller than 20 nm and angle-independent emission, with spectral shifts smaller than 10 nm over a 60° angular tilt.

A triarylamine-based macrocyclic donor is adopted to design new blue thermally activated delayed fluorescence (TADF) emitter. The restricted conformation of macrocyclic donor twisting against the dimethyl substituted phenylene bridge leads to the reduced singlet–triplet energy difference (ΔE _ST) as well as the enhanced horizontal ratio of emission dipole. These beneficial effects contribute to a highly efficient blue TADF organic light-emitting diode.

Abstract

This work reports the incorporation of a triphenylamine-based macrocyclic donor to design new donor-π-acceptor-configured blue thermally activated delayed fluorescence (TADF) emitters. The X-ray structure analyses manifest the degree of twisted conformations that can be modulated by methyl substituents of the π-bridge and macrocyclic donor, leading to well-separated highest occupied natural transition orbital and lowest unoccupied natural transition orbital frontier orbitals, thus sufficiently small singlet–triplet energy difference (ΔE _ST) for TADF. The theoretical analyses elucidate the structure–property relationship and reveal the beneficial effect of macrocyclic donor on increasing reverse intersystem crossing (RISC) process that can contribute to improved triplet-upconversion efficiency. The blue device employing c-NN-TRZ as emitter gave a maximum external quantum efficiecny (EQE_max) of 26.3% as compared to that (19.1%) of the device using the model compound DPA-MeTRZ without the macrocyclic donor, suggesting the contribution of macrocyclic donor to enhance device performance. Benefiting from the combined advantages of macrocyclic donor and methyl substituents, the device incorporating c-NN-MeTRZ as emitter achieves an outstanding EQE_max of 32.2%, which is attributed to the more horizontally oriented emission dipoles as well as the significantly accelerated RISC rate constant (k _RISC) resulting from reduced ΔE _ST. This work represents a new strategy of designing twisted TADF emitter incorporating macrocyclic donor to achieve highly efficient blue device.

Nature Photonics, Published online: 12 January 2023; doi:10.1038/s41566-022-01138-0

A thin-film of crystalline organic semiconductors yields a bright, efficient deep-blue OLED.

Anhydrous polyphosphoric acid is proposed as an enabler for creating an intimate Li | garnet interface with electron-blocking characteristics, resulting in ultralow interfacial impedance, a fast charge–discharge rate, and remarkable long durability of all-solid-state Li metal symmetric and full cells.

Abstract

Garnet-based solid-state Li-metal batteries (GSSBs) have the merits of high energy density and high safety. However, the realization of a stable and well-matched Li|garnet interface for GSSBs remains challenging due to electron leakage and lithiophobic Li₂CO₃ impurity. To address these issues, herein, new surface chemistry is reported that converts the undesired Li₂CO₃ contaminant into an ultra-thin lithium polyphosphate (Li-PPA) layer through anhydrous polyphosphoric acid -induced in situ substitution reaction without damaging the water-sensitive garnet electrolyte. In particular, the Li-PPA interlayer not only facilitates the homogenous spreading of molten Li but also creates a robust electron-blocking shield to suppress Li dendrite formation. As a result, the assembled Li symmetric cell exhibits a low interfacial impedance (4 Ω cm²) and high critical current density (1.8 mA cm⁻²) at 25 °C, which enables the cell to continuously cycle over 2500 h at 0.2 mA cm⁻². Furthermore, the GSSBs paired with LiFePO₄ deliver a high capacity of 149.3 mAh g⁻¹ at 1 C and maintain 92.3% of the initial capacity after 500 cycles and can be used for solar energy storage, suggesting the feasibility of this interfacial engineering strategy for GSSBs.

This review summarizes the structural modification strategies of organic small-molecule semiconductors with high electron mobilities, a promising candidate for the construction of next-generation complementary organic logic-digital circuits, to achieve chemical stability and high electron transport properties. In addition, the applications of n-type small-molecule semiconductor materials based on high mobility in organic electronic devices, such as organic field-effect transistors, organic light-emitting transistors, organic photodetectors, and gas sensors, are introduced.

Abstract

Organic electronics has made great progress in the past decades, which is inseparable from the innovative development of organic electronic devices and the diversity of organic semiconductor materials. It is worth mentioning that both of these great advances are inextricably linked to the development of organic high-performance semiconductor materials, especially the representative n-type organic small-molecule semiconductor materials with high electron mobilities. The n-type organic small molecules have the advantages of simple synthesis process, strong intermolecular stacking, tunable molecular structure, and easy to functionalize structures. Furthermore, the n-type semiconductor is a remarkable and important component for constructing complementary logic circuits and p-n heterojunction structures. Therefore, n-type organic semiconductors play an extremely important role in the field of organic electronic materials and are the basis for the industrialization of organic electronic functional devices. This review focuses on the modification strategies of organic small molecules with high electron mobility at molecular level, and discusses in detail the applications of n-type small-molecule semiconductor materials with high mobility in organic field-effect transistors, organic light-emitting transistors, organic photodetectors, and gas sensors.

Nature Photonics, Published online: 09 January 2023; doi:10.1038/s41566-022-01106-8

An organoboron-emitter, DBTN-2, yields a green organic light-emitting diode with ultrapure colour and high efficiency.