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High efficiency???low efficiency roll-off and long lifetime fluorescent white organic light-emitting diodes based on strategic management of triplet excitons via triplet-triplet annihilation up-conversion and phosphor sensitization
摘要： The simultaneous realization of high efficiency, low efficiency roll-off, long lifetime and stable electroluminescence (EL) spectra in fluorescent white organic light-emitting diodes (WOLEDs) is still a huge challenge. Here, we used a triplet-triplet annihilation up-conversion (TTA-UC) material as blue emission layer and phosphor sensitized fluorescent emitter as red emission layer and introduced a bipolar interlayer between them to fabricate high efficiency, low efficiency roll-off and long lifetime fluorescent WOLEDs. It is clearly seen that the bipolar interlayer not only efficiently distributed the singlet and triplet excitons, but also significantly stabilized the EL spectra. Thus, the resulting two-color fluorescent WOLEDs exhibited the maximum current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) of 26.9 cd A-1, 22.3 lm W-1 and 12.8%, and remained 25.9 cd A-1, 16.9 lm W-1 and 12.1% at the luminance of 1000 cd m-2 and 23.1 cd A-1, 10.6 lm W-1 and 10.7% at the luminance of 10000 cd m-2, respectively, and the operational lifetime LT50 (50% decay, initial luminance of 1000 cd m-2) was also up to 984 h. It can be seen that these devices also showed stable EL spectra with Commission Internationale de I’Eclairage (CIE) of (0.51, 0.41) from 1000 cd m-2 to 5000 cd m-2 luminance. Furthermore, the fabricated three-color fluorescent WOLEDs by further introducing a green fluorescent emitter, also showed high efficiencies of 15.5 cd A-1, 13.0 lm W-1 and 8.1% and stable EL spectra with CIE of (0.43, 0.36) form 1000 cd m-2 to 5000 cd m-2 luminance. More importantly, their CE and EQE exhibited an increasing tendency with the luminance, a fully negligible efficiency roll-off. This design strategy provides a potential route towards high performance fluorescent WOLEDs.
关键词： fluorescent WOLEDs,bipolar interlayer,high efficiency,triplet-triplet annihilation up-conversion,phosphor sensitization,long lifetime,low efficiency roll-off
更新于2025-09-23 15:21:01
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Ultrafast dynamics in van der Waals heterostructures
摘要： Van der Waals heterostructures are synthetic quantum materials composed of stacks of atomically thin two-dimensional (2D) layers. Because the electrons in the atomically thin 2D layers are exposed to layer-to-layer coupling, the properties of van der Waals heterostructures are defined not only by the constituent monolayers, but also by the interactions between the layers. Many fascinating electrical, optical and magnetic properties have recently been reported in different types of van der Waals heterostructures. In this Review, we focus on unique excited-state dynamics in transition metal dichalcogenide (TMDC) heterostructures. TMDC monolayers are the most widely studied 2D semiconductors, featuring prominent exciton states and accessibility to the valley degree of freedom. Many TMDC heterostructures are characterized by a staggered band alignment. This band alignment has profound effects on the evolution of the excited states in heterostructures, including ultrafast charge transfer between the layers, the formation of interlayer excitons, and the existence of long-lived spin and valley polarization in resident carriers. Here we review recent experimental and theoretical efforts to elucidate electron dynamics in TMDC heterostructures, extending from timescales of femtoseconds to microseconds, and comment on the relevance of these effects for potential applications in optoelectronic, valleytronic and spintronic devices.
关键词： spin and valley polarization,charge transfer,valleytronic,transition metal dichalcogenide,Van der Waals heterostructures,excited-state dynamics,spintronic devices,interlayer excitons,optoelectronic
更新于2025-09-23 15:21:01
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Opportunities and challenges of interlayer exciton control and manipulation
摘要： Advances in van der Waals heterostructures allow the control of interlayer excitons by electrical and other means, promising exciting opportunities for high-temperature exciton condensation and valley–spin optoelectronics.
关键词： TMD bilayers,exciton condensation,van der Waals heterostructures,valley–spin optoelectronics,interlayer excitons
更新于2025-09-23 15:21:01
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Excitation that lasts
摘要： The atomic-scale Legoland of two-dimensional (2D) materials has become a much-frequented scientific playground, with building blocks aplenty to create and explore virtually unlimited stacking configurations. When two or more individual monolayers are placed together to form an artificial homo- or heterostructure with weakly interacting constituent layers, that is where the real van der Waals (vdW) architecture begins. Such creations offer electronic, optical and magnetic phenomena that are often utterly unlike the monolayer case. One notable example is the emergence of a new type of exciton in which the electron and the hole are spatially located in different layers. While the formation of these ‘interlayer’ or ‘indirect’ excitons is not exclusive to vdW structures, such as transition metal dichalcogenide (TMD) bilayers in which these species have been observed so far, the unique properties of the constituent 2D materials stemming from the intrinsic valley physics and the enhanced Coulomb interactions at the 2D limit make for an exciting research journey. Likewise, the much-discussed idea of high-temperature exciton condensation using long-lived interlayer excitons remains a possibility that is yet to be experimentally explored. In contrast to monolayers, vdW layered structures possess an additional degree of freedom: the twist angle that stems from the sensitive dependence of the exciton properties on the interlayer interaction and the structural alignment of the constituent monolayers. This unique feature is of particular importance from the perspective of practical applications as it offers a new means of engineering and manipulation of interlayer excitons.
关键词： TMD heterobilayers,excitons,2D materials,van der Waals structures,interlayer excitons
更新于2025-09-23 15:21:01
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Modifications of ZnO Interlayer to Improve the Power Conversion Efficiency of Organic Photovoltaic Cells
摘要： Power conversion efficiency (PCE) is an important parameter in determining the performance of organic photovoltaics (OPVs). Various factors lead to enhancement of power conversion efficiency. One such factor is doping of electron transport layer. A substantial increase in the power conversion efficiency of inverted organic solar cells is realized by a ZnO doped buffer layer acting as an electron-transport layer. Different works on Li, Cd, Ga, Al doping, introduction of C60 interface layer in ZnO buffer layer and dual doped system of InZnO-BisC60 have been reviewed here. The Al-doped buffer layer device showed the highest increase in power conversion efficiency.
关键词： Power conversion efficiency,Organic photovoltaics,ZnO interlayer,Doping
更新于2025-09-23 15:19:57
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All vacuum deposited and thermally stable perovskite solar cells with F4-TCNQ/CuPc hole transport layer
摘要： Hole transporting layers (HTLs) play a crucial role in realization of efficient and stable perovskite solar cells (PSCs). Copper Phthalocyanine (CuPc) is one of the promising HTLs owing to its thermal stability and favorable band alignment with perovskite absorber. However, the power conversion efficiency (PCE) of PSCs with CuPc HTL is still lag behind highly efficient solar cells. Herein, a p-type F4-TCNQ is employed as an interlayer between the perovskite and CuPc HTL in all vacuum deposited PSCs. The F4-TCNQ interlayer improves the conductivity of both MAPbI3 and CuPc, reduces the shunt pathway and facilitates an efficient photoexcited holes transfer from the valance band of the MAPbI3 to LUMO of the F4-TCNQ. Consequently, a best solar cell device with F4-TCNQ interlayer achieved the PCE of 13.03% with a remarkable improvement in fill factor. Moreover, the devices showed superior stability against thermal stress at 85 ?C over 250 hours and retained ~95% of its initial efficiency. This work demonstrates a significant step towards all vacuum deposited perovskite solar cells with high thermal stability.
关键词： Perovskite solar cells,interlayer,thermal stability,vacuum deposition
更新于2025-09-23 15:19:57
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Simultaneous Power Conversion Efficiency and Stability Enhancement of Cs <sub/>2</sub> AgBiBr <sub/>6</sub> Leada??Free Inorganic Perovskite Solar Cell through Adopting a Multifunctional Dye Interlayer
摘要： Perovskite solar cells (PSCs) are highly promising next-generation photovoltaic devices because of the cheap raw materials, ideal band gap of ≈1.5 eV, broad absorption range, and high absorption coefficient. Although lead-based inorganic-organic PSC has achieved the highest power conversion efficiency (PCE) of 25.2%, the toxic nature of lead and poor stability strongly limits the commercialization. Lead-free inorganic PSCs are potential alternatives to toxic and unstable organic-inorganic PSCs. Particularly, double-perovskite Cs2AgBiBr6-based PSC has received interests for its all inorganic and lead-free features. However, the PCE is limited by the inherent and extrinsic defects of Cs2AgBiBr6 films. Herein, an effective and facile strategy is reported for improving the PCE and stability by introducing an N719 dye interlayer, which plays multifunctional roles such as broadening the absorption spectrum, suppressing the charge carrier recombination, accelerating the hole extraction, and constructing an appropriate energy level alignment. Consequently, the optimizing cell delivers an outstanding PCE of 2.84%, much improved as compared with other Cs2AgBiBr6-based PSCs reported so far in the literature. Moreover, the N719 interlayer greatly enhances the stability of PSCs under ambient conditions. This work highlights a useful strategy to boost the PCE and stability of lead-free Cs2AgBiBr6-based PSCs simultaneously, accelerating the commercialization of PSC technology.
关键词： charge carrier separation,dye interlayer,Cs2AgBiBr6,energy level alignment,perovskite solar cell
更新于2025-09-23 15:19:57
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In situ atomic level studies of thermally controlled interlayer stacking shifts in 2D transition metal dichalcogenide bilayers
摘要： We show interlayer stacking shifts occur in transition metal dichalcogenides (TMD) bilayers due to the strain introduced during sample heating, and attributed to rippling of one layer relative to the other. The atomic structure of the interlayer stacking is studied using annular dark field scanning transmission electron microscopy with an in situ heating holder. Before heating, bilayers show uniform interlayer stacking of AA9 and AB. When heated, contrast change is seen and associated with interlayer stacking changes at the atomic scale due to ripples. When cooled down to room temperature, these contrast features disappear, confirming it is a reversible process that is not related to defects or vacancies. Because the bottom layer is attached to the in situ heating chip made from Si3N4 and the top layer is in contact with the underlying TMD layer with weak van der Waals interaction, the two layers experience different forces during thermal expansion.
关键词： transition metal dichalcogenides,thermal expansion,scanning transmission electron microscopy,interlayer stacking,2D materials
更新于2025-09-23 15:19:57
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Near-direct bandgap WSe <sub/>2</sub> /ReS <sub/>2</sub> type-II pn heterojunction for enhanced ultrafast photodetection and high-performance photovoltaics
摘要： PN heterojunctions comprising layered van der Waals (vdW) semiconductors have been used to demonstrate current-rectifiers, photodetectors, and photovoltaic devices. However, a direct or near-direct heterointerface bandgap for enhanced photogeneration in high light-absorbing few-layer vdW materials remains unexplored. In this work, for the first time, density functional theory calculations show that the heterointerface of few-layer group-6 transition metal dichalcogenide (TMD) WSe2 with group-7 ReS2 results in a sizeable (0.7 eV) near-direct type-II bandgap. The interlayer IR bandgap is confirmed through IR photodetection and micro-photoluminescence measurements demonstrate type-II alignment. Few-layer flakes exhibit ultrafast response time (5 μs) and high responsivity (3 A/W) and large photocurrent-generation and responsivity-enhancement at the hetero-overlap region (10-100×). Large open-circuit voltage of 0.64 V and short-circuit current of 2.6 μA enable high output electrical power. Finally, long term air-stability and facile single contact metal fabrication process make the multi-functional few-layer WSe2/ReS2 heterostructure diode technologically promising for next-generation optoelectronics.
关键词： van der Waals heterostructure,pn heterojunction,ultrafast photodetection,near-direct bandgap,infrared photodetection,interlayer bandgap
更新于2025-09-23 15:19:57
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Conversion efficiency enhancement of methylammonium lead triiodide perovskite solar cells converted from thermally deposited lead iodide via thin methylammonium iodide interlayer
摘要： The thermally deposited thin methylammonium iodide (MAI) interlayer worked as protection layer of poly (3, 4-ethylenedioxythiophene) poly (styrene sulfonate) (PEDOT:PSS) in the thermal deposition of lead iodide (PbI2). And the thin MAI interlayer could be the MAI supplemental layer during converting the thermally deposited PbI2 into perovskite. The performances of perovskite solar cells (SCs) converted from thermally deposited PbI2 were remarkably enhanced by using the thin MAI interlayer on PEDOT:PSS. The short-circuit current density (JSC), fill factor (FF%), and conversion efficiency (h %) of perovskite SCs converted from thermally deposited PbI2 increased with the initial increase in thickness of the thin MAI interlayer and then reduced when the thickness of thin MAI interlayer exceeded 2.2 nm. Perovskite SCs converted from thermally deposited PbI2 with a 2.2 nm-thick thin MAI interlayer obtained the largest JSC, FF%, and h % at 19.44 mA/cm2, 74% and 12.75%, respectively, in our study. And the largest JSC was more than twice larger than that of perovskite SCs converted from thermally deposited PbI2 without thin MAI interlayer. Although the perovskite SCs converted from thermally deposited PbI2 without thin MAI interlayer has h % much less than that of perovskite SCs converted from spin-coated PbI2. The perovskite SCs converted from thermally deposited PbI2 with 2.2 nm-thick thin MAI interlayer had an h % of 12.75%, which was larger than that of perovskite SCs converted from spin-coated PbI2 at 10.57%.
关键词： perovskite,CH3NH3PbI3,thermally deposited thin methylammonium iodide,thin methylammonium iodide interlayer
更新于2025-09-23 15:19:57