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...

We report about rationally designed ultrashort peptide bioinks, overcoming severe limitations in current bioprinting procedures. Bioprinting is increasingly relevant in tissue engineering, regenerative and personalized medicine due to its ability to fabricate complex tissue scaffolds through an automated deposition process. Printing stable large-scale constructs with high shape fidelity and enabling long-term cell survival are major challenges that most existing bioinks are unable to solve. Additionally, they require chemical or UV-cross-linking for the structure-solidifying process which compromises the encapsulated cells, resulting in restricted structure complexity and low cell viability. Using ultrashort peptide bioinks as ideal bodylike but synthetic material, we demonstrate an instant solidifying cellembedding printing process via a sophisticated extrusion procedure under true physiological conditions and at cost-effective low bioink concentrations. Our printed large-scale cell constructs and the chondrogenic differentiation of printed mesenchymal stem cells point to the strong potential of the peptide bioinks for automated complex tissue fabrication.

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Room-temperature electroluminescence (EL) is demonstrated from a light-emitting diode (LED) based on two-dimensional lead halide perovskites, (C6H5NH3)2PbI4. The device has a multilayer structure of ITO/Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate)/(C6H5CH2NH3)2PbI4/Bathophenanthroline/Al. The EL emission peaks at 526 nm with a narrow full width at half maximum of 15 nm, which origins from perovskite exciton emission. The LED device exhibits a maximum luminance of ∼9 cd m−2 at a bias of 5 V.