wileyonlinelibrary.comin obtaining wide energy-gap phosphors, reports regarding highly effi cient blue phosphors that exhibit deep-blue emission with Commission Internationale de l'Eclairage (CIE) y values smaller than 0.15 are exiguous, and their short device lifetimes are not suitable for commercial applications. Adachi et al. developed deepblue OLEDs based on thermally activated delayed fl uorescence (TADF) with CIE coordinates of (0.15, 0.07) and a high EQE of 9.9% at low current density. [ 3 ] However, in this type of device, the serious roll-off in effi ciency will have to be solved. Moreover, deep-blue phosphorescent and TADF devices require host and periphery materials with a high enough triplet energy to confi ne the triplet excitons on the emitter, which remains a challenge. [ 4 ] To address these issues, investigators keep focusing their work on conventional blue fl uorophores, in which stability and high color purity can be readily realized. [ 3,5 ] Furthermore, non-doped fl uorescent devices can play a crucial role in reducing the cost of production and simplifying the manufacturing process of fullcolor displays and white-light sources. Yet, most of the reported devices with non-doped emitting layers have been shown to have an unimpressive external quantum effi ciency (EQE) or insuffi cient deep-blue emission. [ 6 ] Particularly, for simplifi ed single-layer devices, which are greatly in favor to limit the overall cost, reports in which the devices have an EQE of 3% or higher are rare. [ 7 ] Therefore, developing highly effi cient, blue, fl uorescent materials remain a signifi cant challenge.There are several prerequisites for high-performance fl uorescent OLEDs with a non-doped light-emitting layer: 1) fl uorescent molecules with high fl uorescent quantum yields; 2) a good balance between electron and hole injection as well as localizing the carrier-recombination region in the light-emitting layer; 3) appropriate energy levels of light-emitting molecules, which match to that of the periphery layers or electrodes; 4) good fi lmforming property and morphological stability of the organic materials. Generally, unbalanced carrier injection and transportation induces an increase in the driving voltage and a decrease in the device effi ciency. Therefore, ambipolar molecules with a donor-acceptor (D-A) structure that encourages the balance of carrier transport are desirable candidates for high-effi ciency OLEDs with non-doped emitting layers. On the other hand, D-A Study of Confi guration Differentia and Highly Effi cient, Deep-Blue, Organic Light-Emitting Diodes Based on Novel Naphtho[1,2-d ]imidazole DerivativesMing Liu , Xiang-Long Li , Dong Cheng Chen , Zhongzhi Xie , Xinyi Cai , Gaozhan Xie , Kunkun Liu , Jianxin Tang , Shi-Jian Su , * and
perovskite materials. [1][2][3][4][5][6][7] Since 2009, rapid progress has been made on the performance of methylammonium lead halide perovskite (CH 3 NH 3 PbX 3 , X = Cl, Br, I)based PeSCs with a substantial increase in power conversion efficiency (PCE) from 3.8% to a stunning value of more than 22%. [8][9][10] Typically, a PeSC is composed of a perovskite absorber layer sandwiched between the hole and the electron transport layers (HTLs and ETLs, respectively). [11] Upon the absorption of incident light, carriers will generate in the perovskite absorber and transport to HTL or ETL, and finally are collected by the corresponding electrodes. To achieve highly efficient and low-cost PeSCs, great efforts have been devoted to optimizing the perovskite material design, device structures and relevant processing techniques. [1][2][3][4][5][6][7][8][9][12][13][14][15] Apart from the major emphasis on perovskite film processing and interface modification for efficient charge collection, it is still of great challenges to achieve maximum light trapping within the devices and then make the majority of incident light for photoelectric conversion. For instance, the photocurrent density of the reported PeSCs were still lower than the theoretical one of ≈26 mA cm −2 , [16] indicating that quite a large fraction of incident light still remains unused for photocurrent generation. The increased physical thickness of the perovskite absorber allows for better light absorption, which however certainly reduces the charge collection efficiency due to the increased recombination current. To alleviate this contradiction, light-trapping schemes are imperative for effectively enhancing light harvesting efficiencies in PeSCs by increasing the internal scattering and absorption of incident light with lower recombination currents.To date, numerous light manipulation strategies using periodic or random structures have been proposed such as plasmonic structures, [17] microlens array, [18] metal nanoparticles, [19] aperiodic arrays, [20][21][22] microresonators, [23] and optical cavities. [24,25] By introducing these schemes to the appropriate interfaces in thin-film solar cells, light absorption can be effectively enhanced by guiding and retaining the incident light through the enhancement of optical path length or the spatial redistribution of light intensity due to surface plasmon resonances (SPRs). Nevertheless, most of these schemes are limited for the practical adoption in large-area solar cell fabrication Light management holds great promise of realizing high-performance perovskite solar cells by improving the sunlight absorption with lower recombination current and thus higher power conversion efficiency (PCE). Here, a convenient and scalable light trapping scheme is demonstrated by incorporating bioinspired moth-eye nanostructures into the metal back electrode via soft imprinting technique to enhance the light harvesting in organic-inorganic lead halide perovskite solar cells. Comparedto the flat reference cell with a methylammonium le...
We report, for the first time, that an encapsulated silver nanoparticle can be directly converted to a silver nanoshell through a nanoscale localized oxidation and reduction process in the gas phase. Silver can be etched when exposed to a mixture of NH3/O2 gases through a mechanism analogous to the formation of aqueous Tollens' reagent, in which a soluble silver-ammonia complex was formed. Starting with Ag@resorcinol-formaldehyde (RF) resin core-shell nanoparticles, we demonstrate that RF-core@Ag-shell nanoparticles can be prepared successfully when the etching rate and RF thickness were well controlled. Due to the strong surface plasmon resonance (SPR) coupling effect among neighboring silver nanoparticles, the RF@Ag nanoparticle showed great SPR and SERS performance. This process provides a general route to the conversion of Ag-core to Ag-shell nanostructures and might be extended to other systems.
We have demonstrated in this article that both power conversion efficiency (PCE) and performance stability of inverted planar heterojunction perovskite solar cells can be improved by using a ZnO:PFN nanocomposite (PFN: poly[(9,9-bis(3'-(N,N-dimethylamion)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)-fluorene]) as the cathode buffer layer (CBL). This nanocomposite could form a compact and defect-less CBL film on the perovskite/PC61BM surface (PC61BM: phenyl-C61-butyric acid methyl ester). In addition, the high conductivity of the nanocomposite layer makes it works well at a layer thickness of 150 nm. Both advantages of the composite layer are helpful in reducing interface charge recombination and improving device performance. The power conversion efficiency (PCE) of the best ZnO:PFN CBL based device was measured to be 12.76%, which is higher than that of device without CBL (9.00%), or device with ZnO (7.93%) or PFN (11.30%) as the cathode buffer layer. In addition, the long-term stability is improved by using ZnO:PFN composite cathode buffer layer when compare to that of the reference cells. Almost no degradation of open circuit voltage (VOC) and fill factor (FF) was found for the device having ZnO:PFN, suggesting that ZnO:PFN is able to stabilize the interface property and consequently improve the solar cell performance stability.
Film morphology has predominant influence on the performance of multilayered organic light-emitting diodes (OLEDs), whereas there is little reported literature from the angle of the molecular level to investigate the impact on film-forming ability and device performance. In this work, four isomeric cross-linkable electron-transport materials constructed with pyridine, 1,2,4-triazole, and vinylbenzyl ether groups were developed for inkjet-printed OLEDs. Their lowest unoccupied molecular orbital (∼3.20 eV) and highest occupied molecular orbital (∼6.50 eV) levels are similar, which are mainly determined by the 1,2,4-triazole groups. The triplet energies of these compounds can be tuned from 2.51 to 2.82 eV by different coupling modes with the core of pyridine, where the 2,6-pyridine-based compound has the highest value of 2.82 eV. Film formation and solubility of the compounds were investigated. It was found that the 2,6-pyridine-based compound outperformed the 2,4-pyridine, 2,5-pyridine, and 3,5-pyridine-based compounds. The spin-coated blue OLEDs based on the four compounds have achieved over 14.0% external quantum efficiencies (EQEs) at the luminance of 100 cd m, and a maximum EQE of 12.1% was obtained for the inkjet-printed device with 2,6-pyridine-based compound.
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