Metal halide perovskites for light-emitting diodes.

Metal halide perovskites have shown promising optoelectronic properties suitable for light-emitting applications. The development of perovskite light-emitting diodes (PeLEDs) has progressed rapidly over the past several years, reaching high external quantum efficiencies of over 20%. In this Review, we focus on the key requirements for high-performance PeLEDs, highlight recent advances on materials and devices, and emphasize the importance of reliable characterization of PeLEDs. We discuss possible approaches to improve the performance of blue and red PeLEDs, increase the long-term operational stability and reduce toxicity hazards. We also provide an overview of the application space made possible by recent developments in high-efficiency PeLEDs.

Histologic Features of Secondary Syphilis.

BACKGROUND: Secondary syphilis is a sexually transmitted infection, which is referred to as "the great imitator" and has a wide spectrum of clinical manifestations. As a result, it is essential to identify potential secondary syphilis patients with ambiguous clinical manifestation through pathology. OBJECTIVE: We sought to analyze the pathological features of secondary syphilis. METHODS: We analyzed 59 biopsy specimens from 56 patients with secondary syphilis. Cases were classified according to the histological characteristics and clinical features. RESULTS: Necrotic keratinocytes could be observed in 39 of 59 (66.1%) secondary specimens. Plasma cells (86.4%) were the most common finding overall. The presence of Treponema pallidum was detected mostly at the dermal-epidermal junction. There was no statistical significance between pathological features and age, HIV status, or RPR titer. CONCLUSIONS: Necrotic keratinocytes are one of the characteristics of secondary syphilis. The combination of plasma cells, irregular acanthosis, elongated rete ridges, and endothelial swelling should increase the likelihood of syphilis.

Efficient and Tunable Electroluminescence from In Situ Synthesized Perovskite Quantum Dots.

Semiconductor quantum dots (QDs) are among the most promising next-generation optoelectronic materials. QDs are generally obtained through either epitaxial or colloidal growth and carry the promise for solution-processed high-performance optoelectronic devices such as light-emitting diodes (LEDs), solar cells, etc. Herein, a straightforward approach to synthesize perovskite QDs and demonstrate their applications in efficient LEDs is reported. The perovskite QDs with controllable crystal sizes and properties are in situ synthesized through one-step spin-coating from perovskite precursor solutions followed by thermal annealing. These perovskite QDs feature size-dependent quantum confinement effect (with readily tunable emissions) and radiative monomolecular recombination. Despite the substantial structural inhomogeneity, the in situ generated perovskite QDs films emit narrow-bandwidth emission and high color stability due to efficient energy transfer between nanostructures that sweeps away the unfavorable disorder effects. Based on these materials, efficient LEDs with external quantum efficiencies up to 11.0% are realized. This makes the technologically appealing in situ approach promising for further development of state-of-the-art LED systems and other optoelectronic devices.

Design rules for minimizing voltage losses in high-efficiency organic solar cells.

The open-circuit voltage of organic solar cells is usually lower than the values achieved in inorganic or perovskite photovoltaic devices with comparable bandgaps. Energy losses during charge separation at the donor-acceptor interface and non-radiative recombination are among the main causes of such voltage losses. Here we combine spectroscopic and quantum-chemistry approaches to identify key rules for minimizing voltage losses: (1) a low energy offset between donor and acceptor molecular states and (2) high photoluminescence yield of the low-gap material in the blend. Following these rules, we present a range of existing and new donor-acceptor systems that combine efficient photocurrent generation with electroluminescence yield up to 0.03%, leading to non-radiative voltage losses as small as 0.21 V. This study provides a rationale to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.

Serological response to therapy following retreatment of serofast early syphilis patients with benzathine penicillin.

Background: Some syphilitic patients remain in a serologically positive state after the recommended therapy. Although we often retreat patients in clinical practice, the optimal treatment protocol remains uncertain due to the paucity of data regarding serological response to retreatment and long-term outcomes. Methods: We examined rapid plasma reagin serological test results of 70 serofast early syphilis cases who were retreated with 2.4 million units of benzathine penicillin weekly for 3 weeks. Serological retreatment success was defined as a minimum 4-fold decrease in baseline rapid plasma reagin test antibody titre within 6 months. Results: Thirty-four (48.6%) of the patients who failed to achieve serological cure at 6 months after initial therapy achieved serological cure at 12 months. Patients who had higher non-treponemal titres at baseline and at 6 months were more likely to exhibit serological cure after retreatment than those with lower titres. Conclusions: Our results suggest that the incremental benefit of retreating serofast patients with early syphilis is moderate, considering the almost 1:1 ratio of serological response to serofast state at follow-up.

Functional Pyrimidine-Based Thermally Activated Delay Fluorescence Emitters: Photophysics, Mechanochromism, and Fabrication of Organic Light-Emitting Diodes.

A new series of molecules, T1-T4, possessing thermally activated delayed fluorescence (TADF) have been strategically designed and synthesized. Molecules T1-T4 contain the dimethyl acridine as the electron donor, which is linked to either symmetrical or unsymmetrical diphenyl pyrimidine as an acceptor. In comparison to the ubiquitous triazine acceptor, the selection of pyrimidine as an acceptor has advantages of facile functionalization and less stabilized unoccupied π orbitals, so that the energy gap toward the blue region can be accessed. Together with acridine donors, the resulting donor-acceptor functional materials reveal remarkable TADF properties. In the solid state, molecules T1-T4 all exhibit intriguing mechanochromism. The crystal structures, together with spectroscopy and dynamics acquired upon application of stressing, lead us to propose two types of structural arrangement that give distinct emission properties, one with and the other without TADF. Upon fabricating organic light-emitting diodes, the T1-T4 films prepared from sublimation all exhibit dominant TADF behavior; this accounts for their high performance: an electroluminescent emission at λ=490 nm, with an external quantum efficiency of 14.2 %, can be attained when T2 is used as an emitter.

[REGgamma promotes malignant behaviors of lung cancer cells].

OBJECTIVE: To determine the expression of proteasome aotivator gamma (REGgamma) in human lung cancer tissues and cell lines and its association with malignant biological behaviors. METHODS: Immunohistochemistry (IHC) was used to detect the expression of REGgamma in lung cancer and normal lung tissues. The expressions of REGgamma in lung cancer cells and normal epithelial cells were determined by Western blot. The H1975 lung cancer stable cell lines with different levels of REGgamma expression were constructed and their proliferations were evaluated by MTT assay. PI staining was used to assess the influence of REGgamma on cell growth cycle. The effect of REGgamma on the migration of lung cancer cells were observed with the cell scratch experiment. RESULTS: Lung cancer tissues had significantly higher levels of REGgamma expression than normal tissues. Similarly, lung cancer cell lines showed higher levels of REGgamma expression than the normal epithelial cell line. The overexpression of REGgamma enhanced cancer cell proliferations (P < 0.05), promoted more cells into the S+G2/M phase (P < 0.05) and promoted the migration of cancer cells (P < 0.05). All of these effects were reversed after suppression of REGgamma. CONCLUSION: REGgamma facilitates malignant biological behaviors of lung cancers.

Transport Layer Engineering Toward Lower Threshold for Perovskite Lasers.

Charge-transport layers are essential for achieving electrically pumped perovskite lasers. However, their role in perovskite lasing is not fully understood. Here, the role of charge-transport layers on the lasing actions of perovskite films is explored by investigating the amplified spontaneous emission (ASE) thresholds. A largely reduced ASE threshold and enhanced ASE intensity is demonstrated by introducing an additional hole transport layer poly(triaryl amine) (PTAA). It is shown that the key role of the PTAA layer is to accelerate the hot-carrier cooling process by extracting holes in perovskites. With reduced hot holes, the Auger recombination loss is largely suppressed, resulting in decreased ASE threshold. This argument is further supported by the fact that the ASE threshold can be further reduced from 25.7 to 7.2 µJ cm-2 upon switching the pumping wavelength from 400 to 500 nm to directly avoid excess hot-hole generation. This work exemplifies how to further reduce the ASE threshold with transport layer engineering through hot-hole manipulation. This is critical to maintaining the excellent gain properties of perovskites when integrating them into electrical devices, paving the way for electrically pumped perovskite lasers.

Novel bipolar host materials based on 1,3,5-triazine derivatives for highly efficient phosphorescent OLEDs with extremely low efficiency roll-off.

Recently, bipolar host materials have attracted considerable attention because they can achieve balanced charge injection/transport in phosphorescent organic light emitting diodes (PhOLEDs) and consequently obtain excellent device performance. In this work, two bipolar host materials, namely, 3-(4,6-diphenyl-1,3,5-triazin-2-yl)-9-phenyl-9H-carbazole (DPTPCz) and 3-(4,6-diphenoxy-1,3,5-triazin-2-yl)-9-phenyl-9H-carbazole (DPOTPCz), have been designed, synthesized and characterized. With high triplet energy levels of 2.78 and 2.86 eV for DPTPCz and DPOTPCz, respectively, two compounds are considered promising bipolar host materials for PhOLEDs. Blue and green PhOLEDs based on these two new compounds show excellent performances. The phosphorescent devices based on DPTPCz exhibit maximum external quantum efficiencies of 14.4% (for blue device) and 21.2% (for green device), and maintain high efficiencies of 11.9% and 20.0% even at a high luminance of 10,000 cd m(-2).

Spacer Cation Alloying in Ruddlesden-Popper Perovskites for Efficient Red Light-Emitting Diodes with Precisely Tunable Wavelengths.

Perovskite light-emitting diodes (PeLEDs) have recently shown significant progress with external quantum efficiencies (EQEs) exceeding 20%. However, PeLEDs with pure-red (620-660 nm) light emission, an essential part for full-color displays, remain a great challenge. Herein, a general approach of spacer cation alloying is employed in Ruddlesden-Popper perovskites (RPPs) for efficient red PeLEDs with precisely tunable wavelengths. By simply tuning the alloying ratio of dual spacer cations, the thickness distribution of quantum wells in the RPP films can be precisely modulated without deteriorating their charge-transport ability and energy funneling processes. Consequently, efficient PeLEDs with tunable emissions between pure red (626 nm) and deep red (671 nm) are achieved with peak EQEs up to 11.5%, representing the highest values among RPP-based pure-red PeLEDs. This work opens a new route for color tuning, which will spur future developments of pure-red or even pure-blue PeLEDs with high performance.

Color-Stable Blue Light-Emitting Diodes Enabled by Effective Passivation of Mixed Halide Perovskites.

Bandgap tuning through mixing halide anions is one of the most attractive features for metal halide perovskites. However, mixed halide perovskites usually suffer from phase segregation under electrical biases. Herein, we obtain high-performance and color-stable blue perovskite LEDs (PeLEDs) based on mixed bromide/chloride three-dimensional (3D) structures. We demonstrate that the color instability of CsPb(Br1-xClx)3 PeLEDs results from surface defects at perovskite grain boundaries. By effective defect passivation, we achieve color-stable blue electroluminescence from CsPb(Br1-xClx)3 PeLEDs, with maximum external quantum efficiencies of up to 4.5% and high luminance of up to 5351 cd m-2 in the sky-blue region (489 nm). Our work provides new insights into the color instability issue of mixed halide perovskites and can spur new development of high-performance and color-stable blue PeLEDs.

Single-emissive-layer all-perovskite white light-emitting diodes employing segregated mixed halide perovskite crystals.

Metal halide perovskites have demonstrated impressive properties for achieving efficient monochromatic light-emitting diodes. However, the development of white perovskite light-emitting diodes (PeLEDs) remains a big challenge. Here, we demonstrate a single-emissive-layer all-perovskite white PeLED using a mixed halide perovskite film as the emissive layer. The perovskite film consists of separated mixed halide perovskite phases with blue and red emissions, which are beneficial for suppressing halide anion exchange and preventing charge transfer. As a result, the white PeLED shows balanced white light emission with Commission Internationale de L'Eclairage coordinates of (0.33, 0.33). In addition, we find that the achievement of white light emission from mixed halide perovskites strongly depends on effective modulation of the halide salt precursors, especially lead bromide and benzamidine hydrochloride in our case. Our work provides very useful guidelines for realizing single-emissive-layer all-perovskite white PeLEDs based on mixed halide perovskites, which will spur the development of high-performance white PeLEDs.

Intermediate-phase-assisted low-temperature formation of γ-CsPbI3 films for high-efficiency deep-red light-emitting devices.

Black phase CsPbI3 is attractive for optoelectronic devices, while usually it has a high formation energy and requires an annealing temperature of above 300 °C. The formation energy can be significantly reduced by adding HI in the precursor. However, the resulting films are not suitable for light-emitting applications due to the high trap densities and low photoluminescence quantum efficiencies, and the low temperature formation mechanism is not well understood yet. Here, we demonstrate a general approach for deposition of γ-CsPbI3 films at 100 °C with high photoluminescence quantum efficiencies by adding organic ammonium cations, and the resulting light-emitting diode exhibits an external quantum efficiency of 10.4% with suppressed efficiency roll-off. We reveal that the low-temperature crystallization process is due to the formation of low-dimensional intermediate states, and followed by interionic exchange. This work provides perspectives to tune phase transition pathway at low temperature for CsPbI3 device applications.

Perovskite-molecule composite thin films for efficient and stable light-emitting diodes.

Although perovskite light-emitting diodes (PeLEDs) have recently experienced significant progress, there are only scattered reports of PeLEDs with both high efficiency and long operational stability, calling for additional strategies to address this challenge. Here, we develop perovskite-molecule composite thin films for efficient and stable PeLEDs. The perovskite-molecule composite thin films consist of in-situ formed high-quality perovskite nanocrystals embedded in the electron-transport molecular matrix, which controls nucleation process of perovskites, leading to PeLEDs with a peak external quantum efficiency of 17.3% and half-lifetime of approximately 100 h. In addition, we find that the device degradation mechanism at high driving voltages is different from that at low driving voltages. This work provides an effective strategy and deep understanding for achieving efficient and stable PeLEDs from both material and device perspectives.

Embryonic stem cell therapy of heart failure in genetic cardiomyopathy.

Pathogenic causes underlying nonischemic cardiomyopathies are increasingly being resolved, yet repair therapies for these commonly heritable forms of heart failure are lacking. A case in point is human dilated cardiomyopathy 10 (CMD10; Online Mendelian Inheritance in Man #608569), a progressive organ dysfunction syndrome refractory to conventional therapies and linked to mutations in cardiac ATP-sensitive K(+) (K(ATP)) channel subunits. Embryonic stem cell therapy demonstrates benefit in ischemic heart disease, but the reparative capacity of this allogeneic regenerative cell source has not been tested in inherited cardiomyopathy. Here, in a Kir6.2-knockout model lacking functional K(ATP) channels, we recapitulated under the imposed stress of pressure overload the gene-environment substrate of CMD10. Salient features of the human malignant heart failure phenotype were reproduced, including compromised contractility, ventricular dilatation, and poor survival. Embryonic stem cells were delivered through the epicardial route into the left ventricular wall of cardiomyopathic stressed Kir6.2-null mutants. At 1 month of therapy, transplantation of 200,000 cells per heart achieved teratoma-free reversal of systolic dysfunction and electrical synchronization and halted maladaptive remodeling, thereby preventing end-stage organ failure. Tracked using the lacZ reporter transgene, stem cells engrafted into host heart. Beyond formation of cardiac tissue positive for Kir6.2, transplantation induced cell cycle activation and halved fibrotic zones, normalizing sarcomeric and gap junction organization within remuscularized hearts. Improved systemic function induced by stem cell therapy translated into increased stamina, absence of anasarca, and benefit to overall survivorship. Embryonic stem cells thus achieve functional repair in nonischemic genetic cardiomyopathy, expanding indications to the therapy of heritable heart failure. Disclosure of potential conflicts of interest is found at the end of this article.

Blue perovskite light-emitting diodes: progress, challenges and future directions.

Metal halide perovskites have excellent optical and electrical properties and can be easily processed via low-cost solution-based techniques like blade-coating and inkjet printing, promising a bright future for various optoelectronic applications. Recently, encouraging progress has been made in perovskite light-emitting diodes (PeLEDs). Green, red, and near-infrared PeLEDs have achieved high external quantum efficiencies of more than 20%. However, as historically blue electroluminescence remains challenging in all previous LED technologies, we are witnessing a similar case with the development of blue PeLEDs, an essential part of displays and solid-state lighting, which lag far behind those of their counterparts. Herein, we review the recent progress of blue PeLEDs and discuss the main challenges including colour instability, poor photoluminescence efficiency and emission quenching by interlayers. Future directions are provided to facilitate the development of efficient blue PeLEDs.

High-Quality Ruddlesden-Popper Perovskite Films Based on In Situ Formed Organic Spacer Cations.

Ruddlesden-Popper perovskites (RPPs), consisting of alternating organic spacer layers and inorganic layers, have emerged as a promising alternative to 3D perovskites for both photovoltaic and light-emitting applications. The organic spacer layers provide a wide range of new possibilities to tune the properties and even provide new functionalities for RPPs. However, the preparation of state-of-the-art RPPs requires organic ammonium halides as the starting materials, which need to be ex situ synthesized. A novel approach to prepare high-quality RPP films through in situ formation of organic spacer cations from amines is presented. Compared with control devices fabricated from organic ammonium halides, this new approach results in similar (and even better) device performance for both solar cells and light-emitting diodes. High-quality RPP films are fabricated based on different types of amines, demonstrating the universality of the approach. This approach not only represents a new pathway to fabricate efficient devices based on RPPs, but also provides an effective method to screen new organic spacers with further improved performance.