Colloidal FAPbBr3 perovskite nanocrystals for light emission: what's going on? (original) (raw)
Related papers
ACS Nano, 2018
In this paper, we reported the in situ fabrication of highly luminescent formamidinium lead bromide (FAPbBr 3) nanocrystal thin films by dropping toluene as an anti-solvent during the spin-coating with a perovskite precursor solution using 3,3-diphenylpropylamine bromide (DPPA-Br) as a ligand. The resulting films are uniform and composed of 5−20 nm FAPbBr 3 perovskite nanocrystals. By monitoring the solvent mixing of anti-solvent and precursor solution on the substrates, we illustrated the difference between the ligand-assisted reprecipitation (LARP) process and the nanocrystal-pinning (NCP) process. This understanding provides a guideline for film optimization, and the optimized films obtained through the in situ LARP process exhibit strong photoluminescence emission at 528 nm, with quantum yields up to 78% and an average photoluminescence lifetime of 12.7 ns. In addition, an exciton binding energy of 57.5 meV was derived from the temperature-dependent photoluminescence measurement. More importantly, we achieved highly efficient pure green perovskite based light-emitting diode (PeLEDs) devices with an average external quantum efficiency (EQE) of 7.3% (maximum EQE is 16.3%) and an average current efficiency (CE) of 29.5 cd A −1 (maximum CE is 66.3 cd A −1) by adapting a conventional device structure of ITO/PEDOT:PSS/TFB/perovskite film/ TPBi/LiF/Al. It is expected that the in situ LARP process provides an effective methodology for the improvement of the performance of PeLEDs. KEYWORDS: perovskite nanocrystals, quantum dots, in situ fabrication, photoluminescence, light-emitting diode H alide perovskites with a general formula of ABX 3 (A = CH 3 NH 3 + , MA, or NH 2 CH=NH 2 + , FA, or Cs + ; B = Pb 2+ or Sn 2+ ; and X = Br − , I − , or Cl −) are now emerging as a new generation of functional semiconductors for photonics and optoelectronics due to their excellent device performance and low-cost solution processability. 1−4 Considering the light-emitting applications, halide perovskites are desired light emitters with characteristics of being bright, color-tunable, and having narrow-band emissions, which make them attractive materials for fabricating light-emitting diodes (LEDs) and lasers. 5−8 Although perovskite-based LEDs (PeLEDs) have been reported since 1994, 9 efficient devices were achieved only after perovskite nanocrystals (PNCs) were introduced. 10−18 During the past 3 years, the external quantum efficiency (EQE) of PeLEDs significantly increased from 0.01− 0.1% up to 14.36%. 10−25 It has been realized that the
Perovskite light emitting diode based on FAPbBr3
Optics and Photonics Society of Iran, 2019
Recently, organometal halide perovskite has been attracted a lot of attention to be employed in optoelectronic devices. Perovskite desired properties like long carrier diffusion length, high radiative recombination, and pure luminescence introduced these materials as suitable candidates to use in optoelectronic devices. In this study, perovskite LED based on formamidinium lead bromide (FAPbBr3) as the emitter layer is used. Perovskite LED emits green light with λ=537nm that starts emitting at 2.7V.
Colloidal CsPbBr3 Perovskite Nanocrystals: Luminescence beyond
Traditional CdSe-based colloidal quantum dots (cQDs) have interesting photoluminescence (PL) properties. Herein we highlight the advantages in both ensemble and single-nanocrystal PL of colloidal CsPbBr3 nanocrystals (NCs) over the traditional cQDs. An ensemble of colloidal CsPbBr3 NCs (11 nm) exhibits ca. 90% PL quantum yield with narrow (FWHM=86 meV) spectral width. Interestingly, the spectral width of a single-NC and an ensemble are almost identical, ruling out the problem of size-distribution in PL broadening. Eliminating this problem leads to a negligible influence of self-absorption and Fçrster resonance energy transfer, along with batch-to-batch reproducibility of NCs exhibiting PL peaks within 1 nm. Also, PL peak positions do not alter with measurement temperature in the range of 25 to 100 8C. Importantly, CsPbBr3 NCs exhibit suppressed PL blinking with ca. 90% of the individual NCs remain mostly emissive (on-time >85%), without much influence of excitation power.
MATEC Web of Conferences, 2021
Hybrid halide perovskites are semicondoctor materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology. They have size-tunable emissions due to quantum size effects. In this work, the Formamidinium Lead Bromide perovskite CH(NH2)2PbBr3 nanoplatelets (NPLs) were successfully synthesized by ligand-assisted reprecipitation method under room condition, in which the emission color-tunability was realized via quantum size effect without anion–halide mixing, by varying the oleylamine to oleic acid volume ratio as surfactants, while the total amount of oleic acid remained unchanged. We are able to adjust the optical proprieties of FAPbBr3 NPLs and, consequently, their structural properties. The obtained colloidal solutions of FAPbBr3 nanoplatelets with uniform size exhibited different photoluminescence wavelengths covering the spectral region from 440 to 525 nm. The maximum absolute PL quantum yield (PLQY) of the green emission wa...
Efficient perovskite light-emitting diodes featuring nanometre-sized crystallites
Organic–inorganic hybrid perovskite materials are emerging as highly attractive semiconductors for use in optoelectronics. In addition to their use in photovoltaics, perovskites are promising for realizing light-emitting diodes (LEDs) due to their high colour purity, low non-radiative recombination rates and tunable bandgap. Here, we report highly efficient perovskite LEDs enabled through the formation of self-assembled, nanometre-sized crystallites. Large-group ammonium halides added to the perovskite precursor solution act as a surfactant that dramatically constrains the growth of 3D perovskite grains during film forming, producing crystallites with dimensions as small as 10 nm and film roughness of less than 1 nm. Coating these nanometre-sized perovskite grains with longer-chain organic cations yields highly efficient emitters, resulting in LEDs that operate with external quantum efficiencies of 10.4% for the methylammonium lead iodide system and 9.3% for the methylammonium lead bromide system, with significantly improved shelf and operational stability. H ybrid organic–inorganic perovskites are emerging as a new generation of low-cost, solution-processed semiconducting materials with favourable optoelectronic properties such as strong absorption coefficients, tunable bandgap 1,2 , large and balanced electron and hole mobilities, long carrier diffusion lengths, small exciton binding energy 3,4 and unique defect properties with only shallow point defects formed 5. These characteristics have allowed for consistent and rapid progress in solar cell efficiency , which has risen dramatically from 3.8% to over 22% in less than five years due to efforts on perovskite film morphology optimization, interface engineering, and so on 6–17. Owing to their facile solution processing, high colour purity and tunable bandgap 18–22 , hybrid perovskites are also promising for LEDs. Nevertheless, the small exciton binding energy in 3D perovs-kites (methylammonium lead iodide, MAPbI 3 , and methylammo-nium lead bromide, MAPbBr 3) result in small electron–hole capture rates for radiative recombination 18. Therefore, ultrathin per-ovskite layers and/or small perovskite grain size have been employed to spatially confine electrons and holes to promote bimolecular radiative recombination 18–20. Recently, an external quantum efficiency (EQE) of 8.5% for MAPbBr 3-based LEDs has been demonstrated through the formation of MAPbBr 3 nanograins with an average size of 100 nm, and reduction of metallic lead impurities 19. However, due to the rapid crystallization speed of 3D perovskites, grain sizes are generally hundreds of nanometres in size from either one-step or two-step solution processes 13,23,24 , with a resulting large surface roughness. Here, we report a solution process to form highly uniform and ultra-flat perovskite films with nanometre-sized grains that allow us to demonstrate highly efficient LEDs. The addition of long-chain ammonium halides (for example, n-butylammonium halides (BAX, X = I, Br)) in the 3D perovskite precursor solution impedes the growth of 3D perovskite grains and dramatically decreases film roughness to 1 nm. The nanometre-sized grains feature reduced dimensionality, starting a transition from 3D to layered (so-called Ruddlesden–Popper) perovskite structures, manifesting in stronger and blue-shifted photoluminescence (PL) and electroluminescence (EL) compared with the emission from the 3D perovskite. Notably, the EQE of iodide perovskite (I-perovs-kite, BAI:MAPbI 3) LEDs increased from 1.0% to 10.4% due to the incorporation of BAI. Similarly, the EQE of bromide perovskite (Br-perovskite, BABr:MAPbBr 3) LEDs increased from 0.03% to 9.3% following the incorporation of BABr. The power efficiency (PE) and current efficiency (CE) reached 13.0 lm W –1 and 17.1 cd A –1 , respectively, for Br-perovskite LEDs. Furthermore, the shelf stability of unencapsulated I-and Br-perovskite LEDs in N 2 was dramatically improved after adding long-chain halides. Specifically, LEDs without BAX degrade to 60–70% of their initial value within 2 days whereas LEDs with BAX (X = I, Br) show no degradation after storage in the glove box for more than 8 months. Perovskite film formation and characterization To deposit uniform pin-hole-free perovskite films with small grain size, toluene was dropped on the spinning film at an appropriate time to extract the processing solvent (dimethylformamide, DMF), thus halting the morphological evolution and maintaining small crystallite size 25,26. To ensure consistency with the device structure, the optical, morphological and structural properties of I-and Br-perovskite films were probed on poly[N,N′-bis(4-butyl-phenyl)-N,N′-bis(phenyl)-benzidine] (poly-TPD) and poly(N-vinylcarbazole) (PVK), respectively. The perovskite thickness is approximately 80 nm for I-perovskite films and 70 nm for Br-per-ovskite films. Atomic force microscope (AFM) images of MAPbI 3 (Fig. 1a) and MAPbBr 3 (Fig. 1g) films without annealing show that both are very uniform. The root mean square (r.m.s.) roughness is 4.9 nm for the MAPbI 3 film and 3.4 nm for the MAPbBr 3 film, among the most flat and uniform perovskite films reported. Long-chain ammonium ions cannot fill the corner of PbX 4 (X = I, Br, Cl) octahedral layers and therefore induce the formation of layered perovskites 27. Notably, when BAX (X = I, Br) is added into the MAPbX 3 precursor solution, the growth of 3D perovskite grains during the film formation process is dramatically impeded.
Journal of Industrial and Engineering Chemistry, 2020
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Tuneable structural and optical properties of inorganic mixed halide perovskite nanocrystals
Applied Research Wiley-VCH, 2023
Highly fluorescent cesium lead-based (CsPbX 3 , X═Br, Cl, I) inorganic metal halide perovskites semiconductors have gained immense popularity in the last decade due to the economic and straightforward fabrication techniques involved in these materials along with their excellent electrical and optoelectronic properties. Cesium lead halide nanocrystals are well known for their fluorescence in the visible region with extremely high internal quantum efficiencies; thus making them highly suitable for the fabrication of efficient light-emitting diodes, transistors and photodetectors. Although perovskite nanocrystals (NCs) are more fluorescent compared to their bulk counterpart, there have been very few reports on the synthesis and characterization of CsPbX 3 perovskite NCs. In this work, we have synthesized and investigated the CsPbBr 3 and CsPbBr 2 I NCs to understand the fundamental optoelectronic properties and structural integrity in mixed halide perovskite NCs. We have estimated~10 nm average particle size of CsPbBr 3 nanocrystals from the highresolution transmission electron microscopy (HRTEM) while CsPbBr 2 I has~16 nm average particle size with slightly higher polydispersity. Most interestingly, we do not observe any phase segregation of bromide and iodide ions in mixed halide perovskite quantum dots due to finite size effect. This is also confirmed by the energy dispersive X-ray spectroscopy (EDS) mapping data. However, CsPbBr 3 nanocrystals are relatively more stable than the mixed halide perovskite nanocrystals due to fewer defects. Anomalous behavior is observed in the photoluminescence intensity with the variation of precursor concentration indicating a complex nature nanoparticle synthesis.
ACS Nano
Lead halide perovskite nanocrystals are an emerging class of materials that have gained wide interest due to their facile color tuning and high photoluminescence quantum yield. However, the lack of techniques to translate the high performance of nanocrystals into solid films restricts the successful exploitation of such materials in optoelectronics applications. Here, we report a heat-up and large-scale synthesis of quantum-confined, blue-emitting CsPbBr 3 nanoplatelets (NPLs) that self-assemble into stacked lamellar structures. Spin-coated films fabricated from these NPLs show a stable blue emission with a photoluminescence quantum yield (PLQY) of 25%. The morphology and the optoelectronic properties of such films can be dramatically modified by UV-light irradiation under ambient conditions at a high power, which transforms the selfassembled stacks of NPLs into much larger structures, such as square-shaped disks and nanobelts. The emission from the transformed thin films falls within the green spectral region with a record PLQY of 65%, and they manifest an amplified spontaneous emission with a sharp line width of 4 nm at full-width at half-maximum under femtosecond-pulsed excitation. The transformed films show stable photocurrents with a responsivity of up to 15 mA/W and response times of tens of milliseconds and are robust under treatment with different solvents. We exploit their insolubility in ethanol to fabricate green-emitting, all-solution-processed light-emitting diodes with an external quantum efficiency of 1.1% and a luminance of 590 Cd/m 2 .
Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes
Science (New York, N.Y.), 2015
Organic-inorganic hybrid perovskites are emerging low-cost emitters with very high color purity, but their low luminescent efficiency is a critical drawback. We boosted the current efficiency (CE) of perovskite light-emitting diodes with a simple bilayer structure to 42.9 candela per ampere, similar to the CE of phosphorescent organic light-emitting diodes, with two modifications: We prevented the formation of metallic lead (Pb) atoms that cause strong exciton quenching through a small increase in methylammonium bromide (MABr) molar proportion, and we spatially confined the exciton in uniform MAPbBr3 nanograins (average diameter = 99.7 nanometers) formed by a nanocrystal pinning process and concomitant reduction of exciton diffusion length to 67 nanometers. These changes caused substantial increases in steady-state photoluminescence intensity and efficiency of MAPbBr3 nanograin layers.