Perovskite light-emitting diodes based on solution-processed self-organized multiple quantum wells, Nature Photonics, 2016. 10(11) Encouraging performance metrics of light-emitting diodes (LEDs) based on 3Dperovskites, such as low turn-on voltages and external quantum efficiencies (EQEs) of up to 3.5% at high current densities, have been demonstrated 9 . However, the EL quantum efficiency is far behind the limit predicated by ~70% PLQE of the 3D perovskites, mainly due to the existence of current losses caused by incomplete surface coverage of the perovskite films and the fact that the high PLQE can only be obtained at high excitations 8,9 . By using thick (>300 nm) perovskite films, Cho et al.obtained LEDs with over 8% EQE 10 . However, for this device, the turn-on voltage is high and the power efficiency is low, which may result from the thick perovskite layer used. In order to further enhance the performance of 3D perovskite-based LEDs, it is 3 essential to obtain perovskite thin films with both complete surface coverage and high PLQE [8][9][10] . Moreover, device stability, which was proven to be a vital issue in organic-inorganic halide perovskite-based photovoltaics 11 , has not been addressed in perovskite LEDs.The 3D perovskites are actually an extreme case of layered organometal halide perovskites with a general formula of L2(SMX3)n-1MX4, where M, X, L, and S are a divalent metal cation, a halide, and organic cations with long and short chains, respectively ( Fig. 1a) [12][13][14] . Here n is the number of semiconducting MX4 monolayer sheets within the two organic insulating layers (cation L), with n=∞ corresponding to the structure of a 3D perovskite SMX3. With smaller numbers of MX4 layers, quantum confinement effects, such as an increase in bandgap and exciton energy, become important 6,15 . In consequence, the layered perovskites naturally form quantum-well structures. At the opposite extreme, when n=1, the layered perovskites form a monolayer structure of a two-dimensional (2D) perovskite L2MX4. The 2D L2MX4 perovskites generally have good film-formation properties 13 . Nevertheless, the PLQEs of the 2D perovskites are rather low at room temperature, owing to fast exciton quenching rates 6,7 . LEDs based on the 2D perovskites have been attempted, while the devices are either very low in efficiency or only operational at cryogenic temperatures [16][17][18] . Here we demonstrate very efficient (up to 11.7% EQE) and high-brightness EL achievable at room temperature by using solution-processed perovskite multiple quantum wells (MQWs) with an energy cascade, which can combine the advantages of 2D and 3D perovskites. We note, a relevant perovskite LED work 19 which shows a peak EQE of 8.8% has been published online during the revision of this paper.A precursor solution of 1-naphthylmethylamine iodide (NMAI), formamidinium iodide (FAI), and PbI2 with a molar ratio of 2:1:2 dissolved in N,N-dimethylformamide (DMF) was used to deposit perovskite films (see Methods for details), which are abbreviated as NFPI...

High-performance perovskite light-emitting diodes are achieved by an interfacial engineering approach, leading to the most efficient near-infrared devices produced using solution-processed emitters and efficient green devices at high brightness conditions.

Efficiency roll-off is a major issue for most types of light-emitting diodes (LEDs), and its origins remain controversial. Here we present investigations of the efficiency roll-off in perovskite LEDs based on two-dimensional layered perovskites. By simultaneously measuring electroluminescence and photoluminescence on a working device, supported by transient photoluminescence decay measurements, we conclude that the efficiency roll-off in perovskite LEDs is mainly due to luminescence quenching which is likely caused by non-radiative Auger recombination. This detrimental effect can be suppressed by increasing the width of quantum wells, which can be easily realized in the layered perovskites by tuning the ratio of large and small organic cations in the precursor solution. This approach leads to the realization of a perovskite LED with a record external quantum efficiency of 12.7%, and the efficiency remains to be high, at approximately 10%, under a high current density of 500 mA cm −2 .

The epidemic of 2019 novel coronavirus, later named as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is still gradually spreading worldwide. The nucleic acid test or genetic sequencing serves as the gold standard method for confirmation of infection, yet several recent studies have reported false-negative results of real-time reverse-transcriptase polymerase chain reaction (rRT-PCR). Here, we report two representative false-negative cases and discuss the supplementary role of clinical data with rRT-PCR, including laboratory examination results and computed tomography features. Coinfection with SARS-COV-2 and other viruses has been discussed as well.

Organolead trihalide perovskites have attracted great attention due to the stunning advances in both photovoltaic and light-emitting devices. However, the photophysical properties, especially the recombination dynamics of photogenerated carriers, of this class of materials are controversial. Here we report that under an excitation level close to the working regime of solar cells, the recombination of photogenerated carriers in solution-processed methylammonium–lead–halide films is dominated by excitons weakly localized in band tail states. This scenario is evidenced by experiments of spectral-dependent luminescence decay, excitation density-dependent luminescence and frequency-dependent terahertz photoconductivity. The exciton localization effect is found to be general for several solution-processed hybrid perovskite films prepared by different methods. Our results provide insights into the charge transport and recombination mechanism in perovskite films and help to unravel their potential for high-performance optoelectronic devices.

Developing novel gold nanoclusters as an electrocatalyst can facilitate a completely reversible reaction between S and Na, achieving advanced high-energy-density room-temperature sodium–sulfur batteries.

This paper reports a facile and scalable process to achieve high performance red perovskite light-emitting diodes (LEDs) by introducing inorganic Cs into multiple quantum well (MQW) perovskites. The MQW structure facilitates the formation of cubic CsPbI perovskites at low temperature, enabling the Cs-based QWs to provide pure and stable red electroluminescence. The versatile synthesis of MQW perovskites provides freedom to control the crystallinity and morphology of the emission layer. It is demonstrated that the inclusion of chloride can further improve the crystallization and consequently the optical properties of the Cs-based MQW perovskites, inducing a low turn-on voltage of 2.0 V, a maximum external quantum efficiency of 3.7%, a luminance of ≈440 cd m at 4.0 V. These results suggest that the Cs-based MQW LED is among the best performing red perovskite LEDs. Moreover, the LED device demonstrates a record lifetime of over 5 h under a constant current density of 10 mA cm . This work suggests that the MQW perovskites is a promising platform for achieving high performance visible-range electroluminescence emission through high-throughput processing methods, which is attractive for low-cost lighting and display applications.

3D organometal halide perovskite. [2] Due to the poor film morphology and strong trap-assisted nonradiative recombination, the device performance is modest, with a peak EQE of 0.76%. Many methods, including interfacial engineering, polymer additive, and antisolvent, have been used to improve the quality of perovskite films. [3,[13][14][15] However, due to the serious trap-assisted nonradiative recombination, the photoluminescence quantum efficiencies (PLQEs) of 3D perovskites at low excitations are quite low, limiting the further improvement of device performance.The emerged multiple-quantum-well (MQW) perovskite has the merits of good film morphology and high PLQE, which is promising to achieve high performance LEDs. The MQW perovskite can be defined as quasi-2D layered perovskite, which is composed of different layered perovskites with naturally formed quantum wells (QWs) (Figure 1). [16][17][18] Generally, the layered perovskite has a formula of L 2 (SMX 3 ) n−1 MX 4 , where L is the large organic cation, S is the small monovalent cation, M is the divalent metal cation, X is the halide anion, and n is the number of MX 4 2− sheets. [19][20][21] In layered perovskites, the MX 4 2− sheet acts as potential well and its number, n, determines well width and the bandgap, while the large organic layer acts as potential barrier and its ionic radius determines the barrier width. It was found that quasi-2D layered perovskite thin film can spontaneously form MQW structure by spin-coating process, which is a mixture of layered perovskites with different n numbers and different bandgaps. [16] The energy transfer process from large bandgap QWs to small bandgap QWs is fast and efficient, resulting in carrier localization and accumulation in low energy QWs. [16,18] Consequently, trap-induced nonradiative recombination can be suppressed and high PLQE can be obtained. Based on the MQWs, the EQE of perovskite LEDs first reaches >10% in 2016. [16,22] Recently, through further suppressing nonradiative recombination and enhancing outcoupling by polymer additive, the peak EQE of near-infrared (NIR) perovskite LEDs based on MQWs has reached 20%. [7] Here, we focus on the unique properties of MQW perovskite and address its potential for high performance LEDs. We then discuss how to control the MQW structure and its effect on perovskite LED performance. Why MQW Perovskites are Promising for High Performance LEDsFor perovskite LEDs, the EQE is intrinsically limited by the properties of perovskite film, which also determine the stability Light-emitting diodes (LEDs) based on solution-processed metal halide perovskites have shown great application potential in energy-efficient lighting and displays. Multiple-quantum-well (MQW) perovskites simultaneously possess high photoluminescence quantum efficiency and good film morphology and stability, making it attractive for high-performance perovskite LEDs. Here, merits of MQW perovskites and the progress in MQW perovskite LEDs are reviewed. Challenges and future directions of perovskite LEDs are ...