t m W t White organic light-emitting diodes (WOLEDs) offer a range of attractive characteristics and are in several regards conceptually different from most currently used light sources. From an application perspective, their advantages include a high power effi ciency that rivals the performance of fl uorescent lamps and inorganic LEDs and the potential for a very low cost of manufacturing. As fl at-panel light sources they are intrinsically glare-free and generate light over a large area. WOLEDs are constantly improving in terms of performance, durability, and manufacturability, but these improvements require joint research efforts in chemistry and the materials sciences to design better materials as well as in physics and engineering to invent new device concepts and design suitable fabrication schemes, a process that has generated many exciting scientifi c questions and answers. This article reviews current developments in the fi eld of WOLEDs and puts a special focus on new device concepts and on approaches to reliable and cost-effi cient WOLED manufacturing.

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White Organic Light Emitting Diodes

Organic light emitting diodes (OLEDs) have been well known for their potential usage in the lighting and display industry. The device efficiency and lifetime have improved considerably in the last three decades. However, for commercial applications, operational lifetime still lies as one of the looming challenges. In this review paper, an in-depth description of the various factors which affect OLED lifetime, and the related solutions is attempted to be consolidated. Notably, all the known intrinsic and extrinsic degradation phenomena and failure mechanisms, which include the presence of dark spot, high heat during device operation, substrate fracture, downgrading luminance, moisture attack, oxidation, corrosion, electron induced migrations, photochemical degradation, electrochemical degradation, electric breakdown, thermomechanical failures, thermal breakdown/degradation, and presence of impurities within the materials and evaporator chamber are reviewed. Light is also shed on the materials and device structures which are developed in order to obtain along with developed materials and device structures to obtain stable devices. It is believed that the theme of this report, summarizing the knowledge of mechanisms allied with OLED degradation, would be contributory in developing better-quality OLED materials and, accordingly, longer lifespan devices.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.202002254

Approaches for Long Lifetime Organic Light Emitting Diodes.

Organic emitters with persistent phosphorescence have shown potential application in optoelectronic devices. However, rational design and phosphorescence tuning are still challenging. Here, a series of metal-free luminophores without heavy atoms and carbonyl groups from commercial/lab-synthesized carbazole and benzene were synthesized to realize tunable molecular emission from fluorescence to phosphorescence by simply substituent variation. All the molecules emit blue fluorescence in both solution and solid state. Upon removal of excitation source, the fluorinated luminophores show obvious phosphorescence. The lab-synthesized carbazole based molecules exhibit a huge lifetime difference to the commercially purchased ones due to the existence of isomer in the latter samples. The small energy gap between singlet and triplet state and low reorganization energy help enhance intersystem crossing to contribute to a more competitive radiative process from triplet to ground state. Blue and white organic light-emitting devices are fabricated by using fluorinated luminophore as emitting layer. Though organic emitters with room temperature phosphorescence (RTP) are attractive for various applications, realizing highly efficient and long lifetime emission remains a challenge. Here, the authors report the role of push-pull electronic effects on emission for organic RTP emitters.

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Tuning molecular emission of organic emitters from fluorescence to phosphorescence through push-pull electronic effects.

Here, a high sensitivity gas sensing ink based on sulfonated rGO (S-rGO) decorated with SnS2 is synthesized for room temperature NO2 and NH3 detection. This sensing ink demonstrated an excellent sensitivity to ppb-level NO2 (17% response to 125 ppb) and sub-ppm-level NH3 (11% response to 1 ppm). The unique absorption properties of SnS2 improve the sensitivity of S-rGO 4.2 and 55 times to NO2 and NH3, respectively. Besides, the superhydrophobicity of the SnS2 endows the sensor with exceptional immunity to high relative humidity (RH). Furthermore, the sensors exhibit negligible degradation to NO2 and less than 15% degradation to NH3 in a wide range of RH from 30 (ambient humidity) to 90%. More importantly, the obtained full-written ink can be applied to common substrates, such as glass, clothes, and paper, and maintain excellent performance after being bent and twisted by 180°.

High Sensitivity, Humidity-Independent, Flexible NO2 and NH3 Gas Sensors Based on SnS2 Hybrid Functional Graphene Ink.

White organic light-emitting diodes (WOLEDs) are of great value in daily life. However, the organic white-emissive single molecules in OLEDs are rare. Herein, we report a group of carbazolyl deriva...

Toward Achieving Single-Molecule White Electroluminescence from Dual Emission of Fluorescence and Phosphorescence

Oxide semiconductors have drawn much attention in recent years due to their outstanding electrical performance, such as relatively high carrier mobility, good uniformity, low process temperature, optical transparency, low cost and especially flexibility. Flexible oxide-based thin film transistors (TFTs) are one of the hottest research topics for next-generation displays, radiofrequency identification (RFID) tags, sensors, and integrated circuits in the wearable field. The carrier transport mechanism of oxide semiconductor materials and typical device configurations of TFTs are firstly described in this invited review. Then, we describe the research progress on flexible oxide-based TFTs, including representative TFTs fabricated on different kinds of flexible substrates, the mechanical stress effect on TFTs and optimized methods to reduce this effect. Finally, an outlook for the future development of oxide-based TFTs is given.

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Research Progress on Flexible Oxide-Based Thin Film Transistors

As one of the most promising technologies for next-generation lighting and displays, white organic light-emitting diodes (WOLEDs) have received enormous worldwide interest due to their outstanding properties, including high efficiency, bright luminance, wide viewing angle, fast switching, lower power consumption, ultralight and ultrathin characteristics, and flexibility. In this invited review, the main parameters which are used to characterize the performance of WOLEDs are introduced. Subsequently, the state-of-the-art strategies to achieve high-performance WOLEDs in recent years are summarized. Specifically, the manipulation of charges and excitons distribution in the four types of WOLEDs (fluorescent WOLEDs, phosphorescent WOLEDs, thermally activated delayed fluorescent WOLEDs, and fluorescent/phosphorescent hybrid WOLEDs) are comprehensively highlighted. Moreover, doping-free WOLEDs are described. Finally, issues and ways to further enhance the performance of WOLEDs are briefly clarified.

Strategies to Achieve High-Performance White Organic Light-Emitting Diodes

Due to the untiring efforts of scientists and researchers on oxide semiconductor materials, processes, and devices, the applications for oxide-based thin film transistors (TFTs) have been researched and promoted on a large scale. With the advantages of relatively high carrier mobility, low off-current, good process compatibility, optical transparency, low cost, and especially flexibility, oxide-based TFTs have already been adapted for not only displays (e.g., liquid crystal display (LCD), organic light emitting diode (OLED), micro-light-emitting diode (Micro-LED), virtual reality/augmented reality (VR/AR) and electronic paper displays (EPD)) but also large-area electronics, analog circuits, and digital circuits. Furthermore, as the requirement of TFT technology increases, low temperature poly-silicon and oxide (LTPO) TFTs, which combine p-type LTPS and n-type oxide TFT on the same substrate, have drawn further interest for realizing the hybrid complementary metal oxide semiconductor (CMOS) circuit. This invited review provides the current progress on applications of oxide-based TFTs. Typical device configurations of TFTs are first described. Then, the strategies to apply oxide-based TFTs for improving the display quality with different compensation technologies and obtaining higher performance integrated circuits are highlighted. Finally, an outlook for the future development of oxide-based TFTs is given.

/pdf/strategies-for-applications-of-oxide-based-thin-film-2dhhyvly.pdf

Strategies for Applications of Oxide-Based Thin Film Transistors

The invention discloses a photovoltaic-thermal comprehensive utilization device capable of automatically adjusting driving power of a circulating pump. The photovoltaic-thermal comprehensive utilization device comprises a photovoltaic power generation system and a heat absorption system, wherein the photovoltaic power generation system comprises a solar cell, a controller, a storage battery and an inverter; the heat absorption system comprises a thermodynamic circulation loop and a user hot-water loop; the thermodynamic circulation loop comprises a water circulation heat collector, a heat exchanger, a water pipeline and a drive pump which are connected through a waterway; the user hot-water loop comprises a heat-insulation water tank, a water inlet valve and a water outlet valve; the heat exchanger is arranged in the heat-insulation water tank and is subjected to heat exchange with water in the heat-insulation water tank; and the solar cell and the water circulation heat collector are integrated into a system heat collector. The photovoltaic-thermal comprehensive utilization device is simple in system structure and good in cooling circulation effect.

Photovoltaic-thermal comprehensive utilization device capable of automatically adjusting driving power of circulating pump and control method

The utility model discloses an automatic adjust circulating pump drive power's photovoltaic light and heat and use multipurposely device, include the photovoltaic power generation system who constitutes by solar cell, controller, battery, dc -to -ac converter, still include hot absorption system, hot absorption system includes heating power circulation circuit and user hot -water return, and heating power circulation circuit includes water path connection's hydrologic cycle heat collector, heat exchanger, water flow pipeline, driving pump, user hot -water return includes holding water box, water intaking valve, outlet valve, the heat exchanger setting in holding water box and with holding water box in the water carry out the heat exchange, solar cell is system's heat collector with the integration of hydrologic cycle heat collector. The utility model discloses system simple structure, refrigeration cycle are respond well.

Lirong Zhang

Papers

Research Progress on Flexible Oxide-Based Thin Film Transistors

Strategies to Achieve High-Performance White Organic Light-Emitting Diodes

Strategies for Applications of Oxide-Based Thin Film Transistors

Photovoltaic-thermal comprehensive utilization device capable of automatically adjusting driving power of circulating pump and control method

Automatic adjust circulating pump drive power's photovoltaic light and heat and use multipurposely device