Query: Perovskite light-emitting diode, Low starting voltage

title: Hybrid perovskite light emitting diodes under intense electrical excitation
abstract: Hybrid perovskite semiconductors represent a promising platform for color tunable light emitting diodes (LEDs) and lasers; however, the behavior of these materials under the intense electrical excitation required for electrically pumped lasing remains unexplored. Here, we investigate methylammonium lead iodide based perovskite LEDs under short pulsed drive at current densities up to 620 A cm 2. At low current density (J 10 A cm 2) we find that the external quantum efficiency (EQE) depends strongly on the time averaged history of the pulse train and show that this curiosity is associated with slow ion movement that changes the internal field distribution and trap density in the device. The impact of ions is less pronounced in the high current density regime ( A cm 2) where EQE roll off is dominated by a combination of Joule heating and charge imbalance yet shows no evidence of Auger loss, suggesting that operation at kA cm 2 current densities relevant for a laser diode should be within reach.Hybrid perovskite semiconductors are promising for wavelength tunable laser diodes but their behavior under intense electrical excitation remains unexplored. Kim et al. investigate perovskite light emitting diodes at current densities nearing 1 kA cm 2 and suggest that a laser diode is within reach.

title: Perovskite Quantum Dots for Application in High Color Gamut Backlighting Display of Light Emitting Diodes
abstract: Lead halide perovskite quantum dots (LHP QDs) exhibit great potential in the backlighting display of light emitting diode applications. Light emitting backlighting with high brightness, low cost, a.

title: Efficient light harvesting from flexible perovskite solar cells under indoor white light emitting diode illumination
abstract: This is the first report of an investigation on flexible perovskite solar cells for artificial light harvesting by using a white light emitting diode (LED) lamp as a light source at 200 and 400 lx, values typically found in indoor environments. Flexible cells were developed using either low temperature sol gel or atomic layer deposited compact layers over conducting polyethylene terephthalate (PET) substrates, together with ultraviolet (UV) irradiated nanoparticle TiO2 scaffolds, a CH3NH3PbI3 xClx perovskite semiconductor, and a spiro MeOTAD hole transport layer. By guaranteeing high quality carrier blocking (via the 10 40 nm thick compact layer) and injection (via the nanocrystalline scaffold and perovskite layers) behavior, maximum power conversion efficiencies (PCE) and power densities of 10.8% and 7.2 mW*cm 2, respectively, at 200 lx, and 12.1% and 16.0 mW*cm 2, respectively, at 400 lx were achieved. These values are the state of the art, comparable to and even exceeding those of flexible dye sensitized solar cells under LED lighting, and significantly greater than those for flexible amorphous silicon, which are currently the main flexible photovoltaic technologies commercially considered for indoor applications. Furthermore, there are significant margins of improvement for reaching the best levels of efficiency for rigid glass based counterparts, which we found was a high of PCE ~24% at 400 lx. With respect to rigid devices, flexibility brings the advantages of being low cost, lightweight, very thin, and conformal, which is especially important for seamless integration in indoor environments.

title: Hole Injection Layer Free Perovskite Light Emitting Diodes.
abstract: In this study, a dual source vapor evaporation method was employed to fabricate the high quality CsPbBr3 thin films with a good crystalline and high surface coverage. Temperature dependent and excitation power dependent photoluminescence measurements were performed to study the optical properties of the CsPbBr3 material. Further, based on the experimental data, the temperature sensitivity coefficient of band gap and exciton binding energy were estimated. More importantly, for the first time, we designed and prepared a hole injection layer free perovskite light emitting diode (LED) based on the Au/MgO/CsPbBr3/n MgZnO/n+ GaN structure, producing an intense green emission ~538 nm) with a high purity. Besides, the device demonstrated a high luminance of 5025 cd/m2, an external quantum efficiency of 1.46% a current efficiency of 1.92 cd/A, and a power efficiency of 1.76 lm/W. We studied in detail the current voltage and electroluminescence properties of the prepared device and proposed the hole generation models and the carrier transport/recombination mechanisms to make these interesting characteristics certain. The results obtained would provide a new and effective strategy for the design and preparation of perovskite LEDs.

title: Interfacial Energy Level Alignment for High Performance All Inorganic Perovskite CsPbBr3 Quantum Dot Based Inverted Light Emitting Diodes.
abstract: All inorganic perovskite light emitting diode (PeLED) has a high stability in ambient atmosphere, but it is a big challenge to achieve high performance of the device. Basically, device design, control of energy level alignment, and reducing the energy barrier between adjacent layers in the architecture of PeLED are important factors to achieve high efficiency. In this study, we report a CsPbBr3 based PeLED with an inverted architecture using lithium doped TiO2 nanoparticles as the electron transport layer (ETL) The optimal lithium doping balances the charge carrier injection between the hole transport layer and ETL, leading to superior device performance. The device exhibits a current efficiency of 3 cd A 1, a luminance efficiency of 2210 cd m 2, and a low turn on voltage of 2.3 V. The turn on voltage is one of the lowest values among reported CsPbBr3 based PeLEDs. A 7 fold increase in device efficiencies has been obtained for lithium doped TiO2 compared to that for undoped TiO2 based devices.

title: Room temperature synthesis of excellent performance CsPb1 Sn Br3 perovskite quantum dots and application in light emitting diodes
abstract: The traditional hot injection (HI) process needs high temperature, inert gas protection, and localized injection operation, which severely hinder their large scale industrialization. Moreover, the CsPb1 xSnxBr3 HI QDs exhibit poor stability. Herein, we report the room temperature (RT) synthesis of CsPb1 xSnxBr3 perovskite QDs by modified ligand assisted reprecipitation (LARP) approach. Compared with the CsPb1 xSnxBr3 HI QDs reported in literatures, the CsPb1 xSnxBr3 RT QDs show higher photoluminescence quantum yield (PLQY) and better stability: the CsPb0.9Sn0.1Br3 RT QDs obtain the highest PLQY of more than 91% and the stability of the film made with this QDs still maintain more than 80% of its original fluorescence strength after 120 days in air environment. Because of the superior PLQY, light emitting diodes (LEDs) based on the RT QDs is constructed, and it exhibits an external quantum efficiency (EQE) of 1.8% a luminance of 1600 cdm 2, a current efficiency of 4.89 cdA 1, a power efficiency of 6.41 lmw 1, and a low on voltage of 3.6 V. The present work provides a feasible method for large scale industrial synthesis of perovskite QDs at room temperature and shows that the CsPb1 xSnxBr3 RT QDs are promising for highly efficient LEDs.

title: Enhanced Performance of Red Perovskite Light Emitting Diodes through the Dimensional Tailoring of Perovskite Multiple Quantum Wells.
abstract: Halide perovskite multiple quantum wells (MQWs) have recently shown great potential in the field of light emitting diodes. We report a facile solution based approach to fabricate dimensionality tunable perovskite MQWs by introducing 1 naphthylmethylammonium (NMA) cations into CsPbI3 perovskites. Through the dimensional tailoring of (NMA)2Csn 1PbnI3n+1 perovskite MQWs, the crystallinity and photoluminescence quantum efficiencies (PLQEs) are significantly improved. We have obtained high performance red perovskite light emitting diodes (PeLEDs) with a luminance of 732 cd m 2 and a maximum external quantum efficiency of 7.3% which are among the best performing red PeLEDs. Significantly, the maximum luminance of our PeLEDs is obtained at a low applied voltage of 3.4 V, with a turn on voltage close to the perovskite band gap (Vturn on 1.9 V) These outstanding performance characteristics demonstrate that dimensional tailoring of perovskite MQWs is a feasible and effective strategy to achieve high performance PeLEDs, which is attractive for full color display applications of perovskites.

title: Rubidium Doping for Enhanced Performance of Highly Efficient Formamidinium Based Perovskite Light Emitting Diodes.
abstract: Organometal halide perovskites (OHPs) have become the most promising optoelectronic material in the past few years with a myriad of applications in the photovoltaic, light emitting, and laser fields. However, for light emitting applications, the low photoluminescence quantum yield (PLQY) of OHP film is critical to hinder the efficiency improvement of OHP film based light emitting diodes (PeLEDs) Herein, we study the effects of rubidium incorporation on the crystal growth, structure, and photoelectric and optical properties of formamidinium lead bromide based (FAPbBr3 based) perovskite films and light emission performance of PeLEDs. It is found that rubidium incorporation can significantly enhance the PLQY of FAPbBr3 film by suppressing the trap density and thus improve the withstand voltage as well as the performance of PeLEDs. When FAPbBr3 film with optimal Rb doping ratio is employed as the light emitter of PeLEDs, the maximum luminance and current efficiency is enhanced by ~10 fold and ~5 fold to 66 353 cd/m2 and 24.22 cd/A compared to the controlled device, respectively, the record performance based on FAPbBr3 PeLEDs so far. The enhanced performance can be chiefly attributed to the increase of PLQY and decrease of trap defect density of perovskite film with rubidium incorporation. Our research is expected to stimulate the development of OHPs for the next generation lighting and display fields.

title: Facile Fabrication of Stretchable Touch Responsive Perovskite Light Emitting Diodes through Using Robust Stretchable Composite Electrodes.
abstract: Perovskite light emitting diode (PeLED) has been vigorously developed in recent years. As it has demonstrated well performance on the rigid substrates, the next important direction of PeLED is their integration with stretchable components to realize stretchable, responsive device. Here, we describe a facile fabrication of stretchable perovskite light emissive touch responsive devices (PeLETDs) through utilizing highly transparent and conductive polyurethane/silver nanowires (PU/AgNWs) as the electrode. Meanwhile, a stretchable tri composite perovskite emissive layer was developed by blending a small amount of poly(ethylene oxide) (PEO) and polyvinylpyrrolidone (PVP) with CsPbBr3. Additionally, a thin PVP layer was introduced at the bottom side of the emissive layer. On one hand, it can further improve the morphology of the emissive layer; on the other hand, it can serve as an electron injection barrier to reduce the high non radiative recombination at the corresponding interface. Further, to fulfill the responsive function of the fabricated PeLEDs, a poly(ethylene terephthalate) (PET) spacer with a 100 mm thickness was inserted between the top electrode and the emissive layer. A stretchable PeLETD is finally demonstrated to possess a low turn on voltage of 2 V with a brightness of 380.5 cd m 2 at 7.5 V, and can sustain 30% uniaxial strain with a small luminance variation of 24% More intriguingly, our stretchable PeLETD exhibited high stability, which could be well touch responsibility, where the luminance is on/off switched for 300 cycles by the repeated pressure.

title: Structure optimization of perovskite quantum dot light emitting diodes.
abstract: Although all inorganic perovskite light emitting diodes (PeLED) have satisfactory stability under an ambient atmosphere, producing devices with high performance is challenging. A device architecture with a reduced energy barrier between adjacent layers and optimized energy level alignment in the PeLED is critical to achieve high electroluminescence efficiency. In this study, we report the optimization of a CsPbBr3 based PeLED device structure with Li doped TiO2 nanoparticles as the electron transport layer (ETL) Optimal Li doping balances charge carrier injection between the hole transport layer (HTL) and ETL, leading to superior performance in both devices. The turn on voltages for devices with Li doped TiO2 nanoparticles were significantly reduced from 7.7 V to 4.9 V and from 3 V to 2 V in the direct and inverted PeLED structures, respectively. The low turn on voltage for green emission is one of the lowest values among the reported CsPbBr3 based PeLEDs. Further investigations show that the device with an inverted structure is superior to the device with a direct structure because the energy barrier for carrier injection was minimized. The inverted structure devices exhibited a current efficiency of 5.6 cd A 1 for the pristine TiO2 ETL, while it was 15.2 cd A 1 for the Li doped TiO2 ETL, a factor of ~2.7 enhancement at 5000 cd m 2.