Highly efficient thermally activated delayed fluorescence (TADF) molecules are in urgent demand for solid‐state lighting and full‐color displays. Here, the design and synthesis of three ...triarylamine‐pyridine‐carbonitrile‐based TADF compounds, TPAPPC, TPAmPPC, and tTPAmPPC, are shown. They exhibit excellent photoluminescence quantum yields of 79−100% with small ΔEST values, fast reverse intersystem crossing (RISC), and high horizontal dipole ratios (Θ// = 86−88%) in the thin films leading to the enhancement of device light outcoupling. Consequently, a green organic light‐emitting diode (OLED) based on TPAmPPC shows a high average external quantum efficiency of 38.8 ± 0.6%, a current efficiency of 130.1 ± 2.1 cd A–1, and a power efficiency of 136.3 ± 2.2 lm W–1. The highest device efficiency of 39.8% appears to be record‐breaking among TADF‐based OLEDs to date. In addition, the TPAmPPC‐based device shows superior operation lifetime and high‐temperature resistance. It is worth noting that the TPA‐PPC‐based materials have excellent optical properties and the potential for making them strong candidates for TADF practical application.
Three 2,6‐diphenylpyridine‐3,5‐dicarbonitrile‐based compounds with excellent photoluminescent quantum yields (79–100%) and high horizontal dipole ratios (86−88%) in the thin films are demonstrated. With two methyl groups on the triarylamines, the spin−orbit coupling is enhanced due to the elevated locally excited triplet states (3LE), leading to a fast reverse intersystem crossing. Green thermally activated delayed fluorescence (TADF) organic light‐emitting diodes based on them exhibit a record‐high external quantum efficiency of 39.8% without any optical extraction technique.
Circularly polarized organic light‐emitting diodes (CP‐OLEDs) are particularly favorable for the direct generation of CP light, and they demonstrate a promising application in 3D display. However, up ...to now, such CP devices have suffered from low brightness, insufficient efficiency, and serious efficiency roll‐off. In this study, a pair of octahydro‐binaphthol (OBN)‐based chiral emitting enantiomers, (R/S)‐OBN‐Cz, are developed by ingeniously merging a chiral source and a luminophore skeleton. These chirality–acceptor–donor (C–A–D)‐type and rod‐like compounds concurrently generate thermally activated delayed fluorescence with a small ΔEST of 0.037 eV, as well as a high photoluminescence quantum yield of 92% and intense circularly polarized photoluminescence with dissymmetry factors (|gPL|) of ≈2.0 × 10−3 in thin films. The CP‐OLEDs based on (R/S)‐OBN‐Cz enantiomers not only display obvious circularly polarized electroluminescence signals with a |gEL| of ≈2.0 × 10−3, but also exhibit superior efficiencies with maximum external quantum efficiency (EQEmax) up to 32.6% and extremely low efficiency roll‐off with an EQE of 30.6% at 5000 cd m−2, which are the best performances among the reported CP devices to date.
Octahydrobinaphthol‐compound‐based circularly polarized delayed fluorescence enantiomers, (R/S)‐OBN‐Cz are developed by merging a chiral source and a luminophore skeleton. The circularly polarized organic light‐emitting diodes based on (R/S)‐OBN‐Cz display intense CP‐electroluminescence signals with a |gEL| of ≈2.0 × 10−3, and achieve superior efficiencies with external quantum efficiency (EQE) up to 32.6% and extremely low efficiency roll‐off with an EQE of 30.6% at 5000 cd m−2.
Luminescent materials with thermally activated delayed fluorescence (TADF) can harvest singlet and triplet excitons to afford high electroluminescence (EL) efficiencies for organic light‐emitting ...diodes (OLEDs). However, TADF emitters generally have to be dispersed into host matrices to suppress emission quenching and/or exciton annihilation, and most doped OLEDs of TADF emitters encounter a thorny problem of swift efficiency roll‐off as luminance increases. To address this issue, in this study, a new tailor‐made luminogen (dibenzothiophene‐benzoyl‐9,9‐dimethyl‐9,10‐dihydroacridine, DBT‐BZ‐DMAC) with an unsymmetrical structure is synthesized and investigated by crystallography, theoretical calculation, spectroscopies, etc. It shows aggregation‐induced emission, prominent TADF, and interesting mechanoluminescence property. Doped OLEDs of DBT‐BZ‐DMAC show high peak current and external quantum efficiencies of up to 51.7 cd A−1 and 17.9%, respectively, but the efficiency roll‐off is large at high luminance. High‐performance nondoped OLED is also achieved with neat film of DBT‐BZ‐DMAC, providing excellent maxima EL efficiencies of 43.3 cd A−1 and 14.2%, negligible current efficiency roll‐off of 0.46%, and external quantum efficiency roll‐off approaching null from peak values to those at 1000 cd m−2. To the best of the authors' knowledge, this is one of the most efficient nondoped TADF OLEDs with small efficiency roll‐off reported so far.
A highly efficient nondoped organic light‐emitting diode affording excellent maxima electroluminescence efficiencies of 43.3 cd A−1 and 14.2%, negligible current efficiency roll‐off of 0.46%, and external quantum efficiency roll‐off approaching null from peak values to those at 1000 cd m−2, is attained based on a robust luminogen featuring aggregation‐induced emission and thermally activated delayed fluorescence.
In this study, the fundamental but previously overlooked factors of charge generation efficiency and light extraction efficiency (LEE) are explored and collaboratively optimized in tandem quantum‐dot ...light‐emitting diodes (QLEDs). By spontaneously forming a microstructured interface, a bulk‐heterojunction‐like charge‐generation layer composed of a poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate)/ZnO bilayer is fabricated and an ideal charge‐generation efficiency surpassing 115% is obtained. The coupling strength of the waveguide mode for the top unit and the plasmon polariton loss for the bottom unit are highly suppressed using precise thickness control, which increases the LEE of the tandem devices. The red tandem QLED achieves an exceptionally low turn‐on voltage for electroluminescence at 4.0 V and outstanding peak external quantum efficiency of 42.9%. The ultralow turn‐on voltage originates from the sequential electroluminescence turn‐on of the two emissive units of the tandem QLED. Benefiting from its unique electroluminescent features, an easily fabricated optical‐electrical dual anti‐counterfeiting display is built by combining a dichromatic tandem QLED with masking technology.
A bulk‐heterojunction‐like CGL enabled by a spontaneously formed microstructured interface is fabricated with a charge‐generation efficiency (CGE) exceeding 115%. Combined with the optimized LEE, a tandem QLED with low turn‐on voltage of 4.0 V and record peak EQE of 42.9% is achieved. An optical‐electrical dual anti‐counterfeiting display based on a dichromatic tandem QLED is proposed.
Aim: To investigate how ecosystem water-use efficiency (WUE) varies spatially under different climate conditions, and how spatial variations in WUE differ from those of transpiration-based water-use ...efficiency (WUEt) and transpiration-based inherent water-use efficiency (IWUEt). Location: Global terrestrial ecosystems. Methods: We investigated spatial patterns of WUE using two datasets of gross primary productivity (GPP) and evapotranspiration (ET) and four biosphere model estimates of GPP and ET. Spatial relationships between WUE and climate variables were further explored through regression analyses. Results: Global WUE estimated by two satellite-based datasets is 1.9 ± 0.1 and 1.8 ± 0.6 g C m⁻² mm⁻¹ lower than the simulations from four process-based models (2.0 ± 0.3 g C m⁻² mm⁻¹) but comparable within the uncertainty of both approaches. In both satellite-based datasets and process models, precipitation is more strongly associated with spatial gradients of WUE for temperate and tropical regions, but temperature dominates north of 50° N. WUE also increases with increasing solar radiation at high latitudes. The values of WUE from datasets and process-based models are systematically higher in wet regions (with higher GPP) than in dry regions. WUEt shows a lower precipitation sensitivity than WUE, which is contrary to leaf- and plant-level observations. IWUEt, the product of WUEt and water vapour deficit, is found to be rather conservative with spatially increasing precipitation, in agreement with leaf- and plant-level measurements. Main conclusions: WUE, WUEt and IWUEt produce different spatial relationships with climate variables. In dry ecosystems, water losses from evaporation from bare soil, uncorrelated with productivity, tend to make WUE lower than in wetter regions. Yet canopy conductance is intrinsically efficient in those ecosystems and maintains a higher IWUEt. This suggests that the responses of each component flux of evapotranspiration should be analysed separately when investigating regional gradients in WUE, its temporal variability and its trends.
Theoretically, the load modulation of carrier amplifiers in Doherty power amplifiers (PAs) achieves a 3-dB higher gain and a higher power-added efficiency (PAE) at a 3-dB back-off power due to the ...two times larger load impedance (Formula Omitted), compared to those at the peak power. In this paper, we analyze the impact of nonlinear Formula Omitted on the gain behavior of heterojunction bipolar transistors (HBT) that shows nearly identical gain and a lower PAE with Formula Omitted. In the environment, the gain distribution of carrier and peaking amplifiers is explained for the linear operation of the Doherty PA with the imperfect load modulation. We also explore harmonic controls for the Doherty PA using class-F matching network to enhance efficiency at a given back-off power and propose a method using a second-harmonic short circuit at the input of the carrier amplifier to compensate for the signal distortion caused by nonlinear Formula Omitted. To validate the efficiency improvement while achieving high linearity, a Doherty PA is fabricated and tested using a long-term evolution signal having a 10-MHz bandwidth and a 16-quadrature amplitude modulation (16-QAM) 7.5-dB peak-to-average power ratio. The proposed Doherty PA achieves a PAE of 45% and an adjacent channel leakage ratio of Formula Omitted at an average output power of 29 dBm. The total consumed power of the proposed PA at this output power represents a reduction by 4.5% and 29%, respectively, to that of a conventional class-F-type Doherty and a class-AB PA.
The marketization of energy price is not only an important part of factor pricing reforms but also decisive for energy efficiency improvement. Thus, this study aims to measure factor price ...distortions and estimate their impact on energy efficiency based on an empirical analysis of 30 provinces of China during 2004–2013 using the stochastic frontier analysis framework. Results yielded three important findings: (1) Technical efficiency was the highest in eastern China, which still remains low at around 0.7980, followed by central China and western China, and there were growing gaps among the above areas. (2) Capital price was relatively high while energy price was relatively low compared with labor price, and the relative allocative efficiency of energy got worse over time. (3) Energy efficiency loss among the three regions showed convergence trends. Policy implications are summarized as follows: (1) Measures such as adjusting energy consumption structure and improving production technology and management levels can reverse the trend of declining technical efficiency. (2) The process of energy price marketization needs to be accelerated. (3) It is necessary to expand the depth and breadth of regional technology diffusion and break the barriers of technology transfer among regions in China.
•Factor price distortions are measured based on Chinese provinces for 2004–2013.•Impacts of factor price distortions on allocative efficiencies are evaluated.•Large regional differences exist in factor price distortion and energy efficiency.•It is necessary to break barriers of technology transfer among regions in China.
On the Efficiency-Fairness Trade-off Bertsimas, Dimitris; Farias, Vivek F.; Trichakis, Nikolaos
Management science,
12/2012, Letnik:
58, Številka:
12
Journal Article
Recenzirano
Odprti dostop
This paper deals with a basic issue: How does one approach the problem of designing the "right" objective for a given resource allocation problem? The notion of what is right can be fairly nebulous; ...we consider two issues that we see as key: efficiency and fairness. We approach the problem of designing objectives that account for the natural tension between efficiency and fairness in the context of a framework that captures a number of resource allocation problems of interest to managers. More precisely, we consider a rich family of objectives that have been well studied in the literature for their fairness properties. We deal with the problem of selecting the appropriate objective from this family. We characterize the trade-off achieved between efficiency and fairness as one selects different objectives and develop several concrete managerial prescriptions for the selection problem based on this trade-off. Finally, we demonstrate the value of our framework in a case study that considers air traffic management.
This paper was accepted by Yossi Aviv, operations management.
The article deals with the determination of general effectiveness of managerial influences on the activity of the railway industry, taking into account such partial indicators as public, functional ...and economic efficiency. appropriate degree of satisfaction of requirements and expectations of consumers on the quality of transport services, as well as the degree of satisfaction of staff with the work conditions are used to assess the public effectiveness of management in railway transport. Functional efficiency of management in railway transport can be estimated by the conformity of managerial decisions to the functional goals and tasks of management, achievement of optimal results within the requirements of state regulation of the industry, etc. The economic efficiency of railway transport management has traditionally been evaluated by the degree of maximization of profitability of freight transport and minimization of losses from passenger transportation with rational use of industry resources.
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