Regulation of quantum spin conversions in a single molecular radical.

Free radicals, generally formed through the cleavage of covalent electron-pair bonds, play an important role in diverse fields ranging from synthetic chemistry to spintronics and nonlinear optics. However, the characterization and regulation of the radical state at a single-molecule level face formidable challenges. Here we present the detection and sophisticated tuning of the open-shell character of individual diradicals with a donor-acceptor structure via a sensitive single-molecule electrical approach. The radical is sandwiched between nanogapped graphene electrodes via covalent amide bonds to construct stable graphene-molecule-graphene single-molecule junctions. We measure the electrical conductance as a function of temperature and track the evolution of the closed-shell and open-shell electronic structures in real time, the open-shell triplet state being stabilized with increasing temperature. Furthermore, we tune the spin states by external stimuli, such as electrical and magnetic fields, and extract thermodynamic and kinetic parameters of the transition between closed-shell and open-shell states. Our findings provide insights into the evolution of single-molecule radicals under external stimuli, which may proof instrumental for the development of functional quantum spin-based molecular devices.

Unraveling Degradation Processes and Strategies for Enhancing Reliability in Organic Light-Emitting Diodes.

Organic light-emitting diodes (OLEDs) have emerged as a promising technology for various applications owing to their advantages, including low-cost fabrication, flexibility, and compatibility. However, a limited lifetime hinders the practical application of OLEDs in electronic devices. OLEDs are prone to degradation effects during operation, resulting in a decrease in device lifetime and performance. This review article aims to provide an exciting overview of OLED degradation effects, highlighting the various degradation mechanisms. Subsequently, an in-depth exploration of OLEDs degradation mechanisms and failure modes is presented. Internal and external processes of degradation, as well as the reactions and impacts of some compounds on OLED performance, are then elucidated. To overcome degradation challenges, the review emphasizes the importance of utilizing state-of-the-art analytical techniques and the role of these techniques in enhancing the performance and reliability of OLEDs. Furthermore, the review addresses the critical challenges of lifetime and device stability, which are crucial for the commercialization of OLEDs. This study also explores strategies to improve OLEDs' lifetime and stability, such as using barrier layers and encapsulation techniques. Overall, this article aims to contribute to the advancement of OLED technology and its successful integration into diverse electronic applications.

Enhancing operational stability of OLEDs based on subatomic modified thermally activated delayed fluorescence compounds.

The realization of operationally stable blue organic light-emitting diodes is a challenging issue across the field. While device optimization has been a focus to effectively prolong device lifetime, strategies based on molecular engineering of chemical structures, particularly at the subatomic level, remains little. Herein, we explore the effect of targeted deuteration on donor and/or acceptor units of thermally activated delayed fluorescence emitters and investigate the structure-property relationship between intrinsic molecular stability, based on isotopic effect, and device operational stability. We show that the deuteration of the acceptor unit is critical to enhance the photostability of thermally activated delayed fluorescence compounds and hence device lifetime in addition to that of the donor units, which is commonly neglected due to the limited availability and synthetic complexity of deuterated acceptors. Based on these isotopic analogues, we observe a gradual increase in the device operational stability and achieve the long-lifetime time to 90% of the initial luminance of 23.4 h at the luminance of 1000 cd m-2 for thermally activated delayed fluorescence-sensitized organic light-emitting diodes. We anticipate our strategic deuteration approach provides insights and demonstrates the importance on structural modification materials at a subatomic level towards prolonging the device operational stability.

Low-voltage-modulated perovskite/organic dual-band photodetectors for visible and near-infrared imaging.

Visible and near-infrared (NIR) light dual-band photodetectors (PDs) have potential applications in signal detection, bioimaging, optical communications and safety monitoring. Herein, we report an ultrafast perovskite/organic heterojunction dual-mode PD with a voltage-modulated photoresponse range in visible and NIR spectra. The PD, comprising a perovskite layer to absorb visible light (500-810 nm) and an organic bulk heterojunction layer for NIR light absorption (810-950 nm), exhibited a switchable spectral response in the visible or NIR bands. The voltage-modulated visible and NIR photoresponses of the PD were attributable to controlled charge photogeneration in perovskite and organic blend thin films under different bias polarities. The device exhibited peak responsivities of 93.5 and 102.2 mA/W in the visible and NIR bands, respectively; a high detectivity of 4.3 × 109 Jones (at forward bias of 0.7 V and incident 625 nm light) and 1.6 × 1012 Jones (at reverse bias of -1.5 V and incident 900 nm light); a fast microsecond response time; and a wide dynamic range (>120 dB) both in the visible mode and NIR mode. Also, this voltage-modulated dual-band PD shows promising applications in visible light and NIR imaging, which is proven by demonstrating a PD array with 25 pixels (5 × 5).

Hybrid modeling of perovskite light-emitting diodes with nanostructured emissive layers.

Perovskite light-emitting diodes (PeLEDs) have attracted much attention due to their superior performance. When a bottleneck of energy conversion efficiency is achieved with materials engineering, nanostructure incorporation proves to be a feasible approach to further improve device efficiencies via light extraction enhancement. The finite-difference time-domain simulation is widely used for optical analysis of nanostructured optoelectronic devices, but reliable modeling of PeLEDs with nanostructured emissive layers remains unmet due to the difficulty of locating dipole light sources. Herein we established a hybrid process for modeling light emission behaviors of such nanostructured PeLEDs by calibrating light source distribution through electrical simulations. This hybrid modeling method serves as a universal tool for structure optimization of light-emitting diodes with nanostructured emissive layers.

Unravelling Alkali-Metal-Assisted Domain Distribution of Quasi-2D Perovskites for Cascade Energy Transfer toward Efficient Blue Light-Emitting Diodes.

Solution processable quasi-2D (Q-2D) perovskite materials are emerging as a promising candidate for blue light source in full-color display applications due to their good color saturation property, high brightness, and spectral tunability. Herein, an efficient energy cascade channel is developed by introducing sodium bromide (NaBr) in phenyl-butylammonium (PBA)-containing mixed-halide Q-2D perovskites for a blue perovskite light-emitting diode (PeLED). The incorporation of alkali metal contributes to the nucleation and growth of Q-2D perovskites into graded distribution of domains with different layer number . The study of excitation dynamics by transient absorption (TA) spectroscopy confirms that NaBr induces more Q-2D perovskite phases with small n number, providing a graded energy cascade pathway to facilitate more efficient energy transfer processes. In addition, the nonradiative recombination within the Q-2D perovskites is significantly suppressed upon Na+ incorporation, as validated by the trap density estimation. Consequently, the optimized blue PeLEDs manifest a peak external quantum efficiency (EQE) of 7.0% emitting at 486 nm with a maximum luminance of 1699 cd m-2 . It is anticipated that these findings will improve the understanding of alkali-metal-assisted optimization of Q-2D perovskites and pave the way toward high-performance blue PeLEDs.

High-performance and stable CsPbBr3 light-emitting diodes based on polymer additive treatment.

Because of their high efficiency and sharp emission, perovskite light-emitting diodes are a promising candidate for next-generation lighting techniques. However, the relatively poor stability of perovskite light-emitting diodes lowers their utility. Therefore, a highly stable perovskite light-emitting diode has to be developed to meet the commercial demand. Herein, we report a highly stable CsPbBr3 light-emitting diode via simple polymer treatment. The addition of 2-methyl-2-oxazoline in perovskite film assists the formation of CsPbBr3 nanocrystals, improving the quality and photoluminescence property of perovskite film. Based on such CsPbBr3 nanocrystals and polymer hybrid film, our device presents a high external quantum efficiency and luminance of around 3.0% and 16 648 cd m-2, respectively. Moreover, an excellent device half-lifetime of more than 2.4 hours has been achieved, under continuous operation at a relatively high initial luminance of 1000 cd m-2, representing one of the most stable PeLEDs operated at such high initial luminance.

Polymer-Assisted In Situ Growth of All-Inorganic Perovskite Nanocrystal Film for Efficient and Stable Pure-Red Light-Emitting Devices.

In the past few years, substantial progress has been made in perovskite light-emitting devices. Both pure green and infrared thin-film perovskite light-emitting devices with external quantum efficiency over 20% have been successfully achieved. However, pure-red and blue thin-film perovskite light-emitting diodes still suffer from inferior efficiency. Therefore, the development of efficient and stable thin-film perovskite light-emitting diodes with pure-red and blue emissions is urgently needed for possible applications as a new display technology and solid-state lighting. Here, we demonstrate an efficient light-emitting diode with pure-red emission based on polymer-assisted in situ growth of high-quality all-inorganic CsPbBr0.6I2.4 perovskite nanocrystal films with homogenous distribution of nanocrystals with size 20-30 nm. With this method, we can dramatically reduce the formation temperature of CsPbBr0.6I2.4 and stabilize its perovskite phase. Eventually, we successfully demonstrate a pure-red-emission perovskite light-emitting diode with a high external quantum efficiency of 6.55% and luminance of 338 cd/m2. Furthermore, the device obtains an ultralow turn-on voltage of 1.5 V and a half-lifetime of over 0.5 h at a high initial luminance of 300 cd/m2.

Fluorescent Supramolecular Polymers Based on Pillar[5]arene for OLED Device Fabrication.

A series of AA/BB-type supramolecular polymers (SP1-3) based on pillar[5]arene host-guest interactions was developed and their photoelectric properties were further evaluated. The formation of SP1 was confirmed by multiple measurements via nuclear magnetic resonance and specific viscosity studies. The electroluminescence properties of SP1-3 were also investigated. As a result of the efficient energy transfer caused by the exciton trapping on narrow band gap guest G2, by applying a doping strategy, the light-emitting color of the resulting polymers could be easily turned from blue to green. Meanwhile, photoluminescent efficiencies up to 81.6% were obtained. All the supramolecular polymers prepared in this work were utilized as the emissive layers (EMLs) in light-emitting devices and a maximum luminance efficiency (LE) of nearly 5 cd A-1 was achieved.