Simple-Structured Phosphorescent Warm White Organic Light-Emitting Diodes with High Power Efficiency and Low Efficiency Roll-off

We present phosphorescent WOLEDs fabricated simply by inserting an ultrathin nondoped orange layer within the blue emissive zone, where an efficient exciplex system is applied as the host. The resulting WOLED shows maximum power efficiency of 75.3 and 63.1 lm/W at the luminance of 1000 cd/m². The exciton density profile in the emitting layer, the operational mechanism and the quenching process at high luminance are systematically investigated by experimental and theoretical methods, from which it is concluded that the efficient utilization of excitons via exciplex host and the wide recombination zone are the key factors for the prominent achievement of high efficiency and greatly reduced efficiency roll-off

FLCN Maintains the Leucine Level in Lysosome to Stimulate mTORC1

<div><p>The intracellular amino acid pool within lysosome is a signal that stimulates the nutrient-sensing mTORC1 signalling pathway. The signal transduction cascade has garnered much attention, but little is known about the sequestration of the signalling molecules within the lysosome. Using human HEK293 cells as a model, we found that suppression of the BHD syndrome gene FLCN reduced the leucine level in lysosome, which correlated with decreased mTORC1 activity. Both consequences could be reversed by supplementation with high levels of leucine, but not other tested amino acids. Conversely, overexpressed FLCN could sequester lysosomal leucine and stimulate mTORC1 in an amino acid limitation environment. These results identify a novel function of FLCN: it controls mTORC1 by modulating the leucine signal in lysosome. Furthermore, we provided evidence that FLCN exerted this role by inhibiting the accumulation of the amino acid transporter PAT1 on the lysosome surface, thereby maintaining the signal level within the organelle.</p></div

FLCN and PAT1 antagonize each other to control mTORC1.

<p>(A) Overexpression of PAT1 inhibits mTORC1. Cells were starved for 50 mins, followed by re-stimulation with complete medium for 10 mins. Three stable lines and one transient expression sample (lane 5) of EGFP-PAT1 were analysed. The predicated molecular weight of EGFP-PAT1 is about 75 kD. Due to post-translational modifications of membrane proteins, it often displays additional large shifted bands in the immunoblotting results (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0157100#pone.0157100.g005" target="_blank">Fig 5</a>). (B-D) PAT1 counteracts FLCN for mTORC1 induction. In all experiments, transient expression (FLCN-HA or EGFP-PAT1) was lasted for 48 hrs; siRNA (FLCN or PAT1) was lasted for 36 hrs before the analysis. The siRNAs of FLCN and PAT1 have been tested before [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0157100#pone.0157100.ref021" target="_blank">21</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0157100#pone.0157100.ref043" target="_blank">43</a>]. Error bars denote the mean ± S.E.M. (n = 3 repeated experiments); * P<0.05, ** P<0.01, Student’s t-test.</p

High leucine antagonizes FLCN-deficiency to stimulate mTORC1.

<p>(A-C) Cells were allowed to express the FLCN shRNA (shFLCN) for 48 hours, followed by stimulation with different doses of the indicated amino acids for another 2 hrs. In A, the treatment with 0.8 mM of leucine means cultured with complete culture medium. (D) Cells were starved with amino acid-free RPMI 1640 medium for 1 hour, stimulated with the indicative amount of leucine for additional 2 hrs. (E) The stimulation with leucine, BafA1 (0.1 μM) or in combination was performed for 2 hrs. In the quantitative analyses, the gray values of pS6K1 were normalized to that of S6K1. Error bars denote the mean ± S.E.M. (n = 3 repeated experiments); *** P<0.001, Student’s t-test. In all the experiments, representative pictures from at least three repeated experiments were presented.</p

FLCN regulates the leucine level in lysosome.

<p>(A) Control (+AA) and staved cells (-AA, for 1 hour) were co-stained for FLCN (red) and LAMP1 (green). DNA was stained with DAPI (blue). Scale bar: 10 μM. Co-localization of FLCN and LAMP1 was measured using the Nikon NIS-Element software and shown by Pearson's correlation coefficient (Pearson's <i>r</i>). (B) Whole cell lysate or the purified lysosomes were analysed by western blotting. Each loaded sample of the purified lysosome was about 30% to that of the whole cell lysate (in total protein). Representative pictures from at least three repeated experiments were presented. (C, D) Quantification analysis of the lysosomal (C) and cytosolic (D) leucine. Data were obtained from three independent experiments and are shown as mean ± S.E.M. Numbers on the column are the relative values that have been normalized to that in control (1.0). * P<0.05, ** P<0.01, *** P<0.001, Student’s t-test.</p

Ectopic FLCN renders cells resistant to starvation for mTORC1 induction.

<p>(A) Control (293) and two FLCN-HA stable cell lines were analysed by western blotting. Starvation was lasted for 1 hour. (B) Cells were starved for 50 mins, stimulated with different amounts of additive leucine for another 30 mins. (C) BafA1 inhibits the ectopic FLCN-stimulated mTORC1. (D, E) Quantitative assay of the lysosomal leucine. Note starvation reduces the lysosomal leucine, but to a lesser extent in the FLCN-HA cells (D); (E) in complete medium (+AA). (G) A picture showing the body size of fly pupae. Heterozygotes from the same crosses without ectopic expression were taken as the control. (H) Fly growth profiles. Error bars denote the mean ± S.E.M. (n = 3 repeated experiments); * P<0.05, ** P<0.01, Student’s t-test.</p

Managing Excitons and Charges for High-Performance Fluorescent White Organic Light-Emitting Diodes

The simultaneous realization of high efficiency, stable spectra, high color rendering index (CRI), and low-efficiency roll-off in a fluorescent white organic light-emitting diode (WOLED) still remains a big challenge. Here, we demonstrate high-performance conventional fluorescent-dopant-based WOLEDs by strategic management of singlet and triplet excitons within an efficient emissive zone. This design consists of two separated red/green sub-EMLs with ultralow doping concentration and a sandwiched sub-EML doped with red and green fluorescent dyes at a relatively high concentration, which can harness all electrogenerated excitons and reduce the energy loss to the utmost extent. Accordingly, the resulting WOLED realizes an external quantum efficiency (EQE) of 18.2% with a maximum power efficiency of 44.6 lm W^–1. At the practical luminance of 1000 cd m^–2 for the lighting source, the EQE still remains as high as 16.2% with a CRI of 82 and stable color spectra. A comprehensive understanding of the device working mechanism is performed to guide design of efficient and stable fluorescent WOLEDs

Boosting the Photocurrent Density of p‑Type Solar Cells Based on Organometal Halide Perovskite-Sensitized Mesoporous NiO Photocathodes

The p–n tandem design of a sensitized solar cell is a novel concept holding the potential to overcome the efficiency limitation of conventional single-junction sensitized solar cells. Significant improvement of the photocurrent density (<i>J</i>_sc) of the p-type half-cell is a prerequisite for the realization of a highly efficient p–n tandem cell in the future. This study has demonstrated effective photocathodes based on novel organometal halide perovskite-sensitized mesoporous NiO in liquid-electrolyte-based p-type solar cells. An acceptably high <i>J</i>_sc up to 9.47 mA cm^–2 and efficiency up to 0.71% have been achieved on the basis of the CH₃NH₃PbI₃/NiO solar cell at 100 mW cm^–2 light intensity, which are significantly higher than those of any previously reported liquid-electrolyte-based p-type solar cells based on sensitizers of organic dyes or inorganic quantum dots. The dense blocking layer made by spray pyrolysis of nickel acetylacetonate holds the key to determining the current flow direction of the solar cells. High hole injection efficiency at the perovskite/NiO interface and high hole collection efficiency through the mesoporous NiO network have been proved by time-resolved photoluminescence and transient photocurrent/photovoltage decay measurements. The limitation of these p-type solar cells primarily rests with the adverse light absorption by the NiO mesoporous film; the secondary limitation arises from the highly viscous ethyl acetate-based electrolyte, which is helpful for the solar cell stability but hinders fluent diffusion into the pore channels, giving rise to a nonlinear dependence of <i>J</i>_sc on the light intensity

Achieving Extreme Utilization of Excitons by an Efficient Sandwich-Type Emissive Layer Architecture for Reduced Efficiency Roll-Off and Improved Operational Stability in Organic Light-Emitting Diodes

It has been demonstrated that the efficiency roll-off is generally caused by the accumulation of excitons or charge carriers, which is intimately related to the emissive layer (EML) architecture in organic light-emitting diodes (OLEDs). In this article, an efficient sandwich-type EML structure with a mixed-host EML sandwiched between two single-host EMLs was designed to eliminate this accumulation, thus simultaneously achieving high efficiency, low efficiency roll-off and good operational stability in the resulting OLEDs. The devices show excellent electroluminescence performances, realizing a maximum external quantum efficiency (EQE) of 24.6% with a maximum power efficiency of 105.6 lm W^–1 and a maximum current efficiency of 93.5 cd A^–1. At the high brightness of 5 000 cd m^–2, they still remain as high as 23.3%, 71.1 lm W^–1, and 88.3 cd A^–1, respectively. And, the device lifetime is up to 2000 h at initial luminance of 1000 cd m^–2, which is significantly higher than that of compared devices with conventional EML structures. The improvement mechanism is systematically studied by the dependence of the exciton distribution in EML and the exciton quenching processes. It can be seen that the utilization of the efficient sandwich-type EML broadens the recombination zone width, thus greatly reducing the exciton quenching and increasing the probability of the exciton recombination. It is believed that the design concept provides a new avenue for us to achieve high-performance OLEDs