This paper reports highly bright and efficient CsPbBr3 perovskite light‐emitting diodes (PeLEDs) fabricated by simple one‐step spin‐coating of uniform CsPbBr3 polycrystalline layers on a ...self‐organized buffer hole injection layer and stoichiometry‐controlled CsPbBr3 precursor solutions with an optimized concentration. The PeLEDs have maximum current efficiency of 5.39 cd A−1 and maximum luminance of 13752 cd m−2. This paper also investigates the origin of current hysteresis, which can be ascribed to migration of Br− anions. Temperature dependence of the electroluminescence (EL) spectrum is measured and the origins of decreased spectrum area, spectral blue‐shift, and linewidth broadening are analyzed systematically with the activation energies, and are related with Br− anion migration, thermal dissociation of excitons, thermal expansion, and electron–phonon interaction. This work provides simple ways to improve the efficiency and brightness of all‐inorganic polycrystalline PeLEDs and improves understanding of temperature‐dependent ion migration and EL properties in inorganic PeLEDs.
Efficient and bright CsPbBr3 perovskite light‐emitting diodes are achieved using a one‐step fabrication of uniform CsPbBr3 polycrystalline layers on a self‐organized buffer hole injection layer without synthesis of quantum dots. A study of the temperature dependence of current hysteresis and electroluminescence spectrum provides understanding of ion migration, nonradiative pathways, and electron–phonon interaction in the CsPbBr3 perovskite light‐emitting diodes.
This review focuses on the importance and the key functions of anode interfacial layers based on conducting polymers in organic and organic–inorganic hybrid perovskite optoelectronics. Insertion of a ...buffer layer between electrode and semiconducting layers is the most common and effective way to control interfacial properties and eventually improve device characteristics, such as luminous efficiency in light‐emitting diodes and power conversion efficiency in solar cells. Conducting polymers are considered as one of the most promising materials for future organic and organic–inorganic hybrid electronics because of advantages such as a simple film‐forming process and ease of tailoring electrical and physical properties; as a result, using these polymers is compatible with the production of large‐area, low‐cost, and solution‐processed flexible optoelectronic devices. This review introduces the limitations of anode buffer layers based on conducting polymers and then we will provide recent research trends of material engineering to overcome these problems.
Conducting polymers are widely used as an anode buffer layer for organic and organic–inorganic hybrid perovskite (OIHP) optoelectronics. Engineering of various materials is reviewed and discussed to overcome limitations of conventional conducting polymers, and their applications as a conducting polymer‐based anode buffer layer in organic and OIHP light‐emitting diodes and solar cells.
Organic–inorganic hybrid perovskite solar cells are fabricated using a water‐soluble, self‐doped conducting polyaniline graft copolymer based on poly(4‐styrenesulfonate)‐g‐polyaniline (PSS‐g‐PANI) as ...an efficient hole‐extraction layer (HEL) because of its advantages, including low‐temperature solution processability, high transmittance, and a low energy barrier with perovskite photoactive layers. Compared with conventional poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) dispersed in water solution, PSS‐g‐PANI molecules are dissolved in water because of the polymeric dopant covalently bonded with PANI, and can steadily remain as an initial solution during long‐term storage and over a wide pH range to fabricate a HEL with fewer surface defects. The built‐in potential and device characteristics are substantially improved because of the surface energy state of PSS‐g‐PANI below Fermi‐energy level. Moreover, the PSS‐g‐PANI mixed with electron‐withdrawing perfluorinated ionomer (PFI) exhibits a higher work function (5.49 eV) and deeper surface energy state below the Fermi level; thus, an ohmic contact at the HEL/methylammonium lead iodide perovskite interface is obtained. Finally, the power conversion efficiency was increased from 7.8% in the perovskite solar cells with PEDOT:PSS to 12.4% in those with the PSS‐g‐PANI:PFI.
A water‐soluble self‐doped poly(styrene sulfonate) grafted polyaniline copolymer (PSS‐g‐PANI) was used to achieve high power conversion efficiency (PCE) in solution‐processed planar heterojunction perovskite solar cells. The PCE was increased from 7.8% in the methylammonium lead iodide perovskite solar cell with poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) to 12.4% in that with PSS‐g‐PANI:perfluorinated ionomer due to good energy level alignment at the hole extraction interface and high transmittance.
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•A new donor–acceptor type green fluorescent emitter, PhBBPP, was synthesized.•Thermal, photophysical, and electrochemical properties of PhBBPP were investigated.•PhBBPP showed high ...thermal stability and efficient intramolecular charge transfer.•A high luminous efficiency of 12.1cd/A was achieved in non-doped OLED.
We synthesized a new donor–acceptor type (D–A type) green fluorescent emitter, 3,7-bis(1-(biphenyl-4-yl)-1H-benzodimidazole-2-yl)-10-phenyl-10H-phenothiazine (PhBBPP), which consists of phenylphenothiazine as an electron donor and biphenylbenzimidazole as an acceptor. Its thermal and photophysical properties, and energy band structure were studied, and also organic light-emitting diodes (OLEDs) with various device structures were fabricated using PhBBPP as an emitting layer. The optimized OLED device with a structure of ITO/NPB (40nm)/PhBBPP (30nm)/TPBi (30nm)/Alq3 (10nm)/LiF (1nm)/Al (100nm) showed a turn-on voltage of 3.4V, a luminous efficiency of 12.1cd/A, and an external quantum efficiency of 4.0% at 100cd/m2 with a maximum luminance of 8200cd/m2.
The fossil record suggests greater diversity of insect leaf feeding during warm climate intervals. Much published work in the paleobotanical literature has been based on the presumed validity of this ...pattern. However, the existence of this pattern in nature has never been tested from the present-day world. Here we ask, is it true that on average, in warmer climates, a leaf is being eaten in more ways?
We compared forests at seven sites in northern Florida (30° N, MAT ca. 19.5
°C) to seven sites across the north-eastern USA (40–42° N, MAT 7–9
°C). Presence and absence of damage types were determined using a standard leaf damage guide; 93 damage types were found in the Florida samples and 80 in the north-eastern samples.
In bulk floras, there was a consistent difference in damage diversity, on a per-leaf basis (as in the fossil studies), between Florida and north-eastern sites. Florida sites had a greater number of damage types. When northern and southern populations of individual tree species were compared, higher southern damage diversity was found in four species (
Acer rubrum,
Acer saccharum,
Fagus grandifolia, and
Quercus coccinea), though with no difference with latitude in a fifth species (
Quercus alba).
These results appear to validate that the trend seen in the fossil record is not a spurious effect of site differences. They also extend a pattern seen in deep time into the present day, adding greatly to its generality.
Although several transparent conducting materials such as carbon nanotubes, graphene, and conducting polymers have been intensively explored as flexible electrodes in optoelectronic devices, their ...insufficient electrical conductivity, low work function, and complicated electrode fabrication processes have limited their practical use. Herein, a 2D titanium carbide (Ti3C2) MXene film with transparent conducting electrode (TCE) properties, including high electrical conductivity (≈11 670 S cm−1) and high work function (≈5.1 eV), which are achieved by combining a simple solution processing with modulation of surface composition, is described. A chemical neutralization strategy of a conducting‐polymer hole‐injection layer is used to prevent detrimental surface oxidation and resulting degradation of the electrode film. Use of the MXene electrode in an organic light‐emitting diode leads to a current efficiency of ≈102.0 cd A−1 and an external quantum efficiency of ≈28.5% ph/el, which agree well with the theoretical maximum values from optical simulations. The results demonstrate the strong potential of MXene as a solution‐processable electrode in optoelectronic devices and provide a guideline for use of MXenes as TCEs in low‐cost flexible optoelectronic devices.
A solution‐processed transparent conducting electrode with desirable properties including high electrical conductivity (≈11 668 S cm−1) and work function (≈5.1 eV) is achieved by using a 2D titanium carbide (Ti3C2) MXene thin film. Precise control of the surface chemical composition and a neutralized hole‐injection layer prevent detrimental surface/interface oxidation of the MXene and enable a high‐efficiency organic light‐emitting diode that uses the solution‐processed MXene electrode.
Organic–inorganic hybrid perovskites (OHPs) are promising emitters for light‐emitting diodes (LEDs) due to the high color purity, low cost, and simple synthesis. However, the electroluminescent ...efficiency of polycrystalline OHP LEDs (PeLEDs) is often limited by poor surface morphology, small exciton binding energy, and long exciton diffusion length of large‐grain OHP films caused by uncontrolled crystallization. Here, crystallization of methylammonium lead bromide (MAPbBr3) is finely controlled by using a polar solvent‐soluble self‐doped conducting polymer, poly(styrenesulfonate)‐grafted polyaniline (PSS‐g‐PANI), as a hole injection layer (HIL) to induce granular structure, which makes charge carriers spatially confined more effectively than columnar structure induced by the conventional poly(3,4‐ethylenedioythiphene):polystyrenesulfonate (PEDOT:PSS). Moreover, lower acidity of PSS‐g‐PANI than PEDOT:PSS reduces indium tin oxide (ITO) etching, which releases metallic In species that cause exciton quenching. Finally, doubled device efficiency of 14.3 cd A‐1 is achieved for PSS‐g‐PANI‐based polycrystalline MAPbBr3 PeLEDs compared to that for PEDOT:PSS‐based PeLEDs (7.07 cd A‐1). Furthermore, PSS‐g‐PANI demonstrates high efficiency of 37.6 cd A‐1 in formamidinium lead bromide nanoparticle LEDs. The results provide an avenue to both control the crystallization kinetics and reduce the migration of In released from ITO by forming OIP films favorable for more radiative luminescence using the polar solvent‐soluble and low‐acidity polymeric HIL.
Perovskite crystallization kinetics can be finely controlled using a self‐doped conducting polymer as the hole injection layer of perovskite light‐emitting diodes (PeLEDs). Polar solvent‐soluble self‐doped polyaniline facilitates crystallization control by impeding the solvent evaporation from cast perovskite precursor pseudo‐films. The finely controlled crystallization contributes to achieving granular nanograin structure, which can strengthen the exciton confinement for boosting luminescence efficiency of PeLEDs.
We investigated the solid state solvation effect (SSSE) of a donor–acceptor (D–A) type green fluorescent emitter, 3,7-bis(benzimidazol-2-yl)-10-methylphenothiazine (BBMP), and fabricated white ...organic light-emitting diodes (OLEDs) by utilizing SSSE. After having confirmed that BBMP showed a large solvatochromic photoluminescence spectral shift not only in liquid solutions but also in solid solutions, we induced a sky-blue electroluminescence (EL) by doping the green-emitting BBMP in non-polar host materials. The emission spectrum of BBMP blue-shifted as the polarity of host material decreased, and white OLEDs were obtained by integrating an additional orange light-emitting material, Rubrene, into this sky-blue-emitting OLED structure. When 9, 10-di(naphtha-2-yl)anthracene(ADN) was employed as a non-polar host of BBMP, the device exhibited a sky-blue (λpeak,EL = 475 nm) emission by SSSE with evidently improved EL properties: the luminous efficiency, the external quantum efficiency, and the maximum luminance were 10.4 cd/A, 3.5%, and 46,600 cd/m2, respectively. Finally, the white OLED with an optimized structure of ITO/NPB (20 nm)/ADN:Rubrene (20 nm)/NPB (2 nm)/ADN:BBMP (20 nm)/TPBi (20 nm)/Alq3 (10 nm)/LiF (1 nm)/Al (100 nm) demonstrated a luminous efficiency of 5.3 cd/A, an external quantum efficiency of 1.3%, and a maximum luminance of 15,200 cd/m2 with CIE coordinates of (0.32, 0.42) at 100 mA/cm2.
•The solid state solvation effect (SSSE) of a donor–acceptor type emitter, BBMP, was investigated.•BBMP showed a large solvatochromic spectral shift in both PL and EL spectra.•The emission color was blue-shifted from green to sky-blue by doping BBMP in a non-polar host, ADN.•The WOLED was successfully achieved by incorporating the SSSE-based sky-blue emitting layer.
An ideal conducting polymer anode (CPA) in organic and perovskite light-emitting diodes (LEDs) requires high electrical conductivity κ, high work function WF, and prevention of exciton quenching ...between an anode and an overlying emitting layer. However, increasing the κ and WF at the same time has been a very challenging unsolved issue due to their trade-off relationship: previous approaches to increase the WF have reduced the films’ κ and vice versa. Therefore, delicate molecular scale control of the conducting polymer compositions are required to solve this fundamental issue. Here, we introduce an effective molecular scale control strategy to decouple the WF with κ in a CPA while maintaining blocking capability of exciton quenching. This change resulted in a high current efficiency up to 52.86 cd A−1 (10.93% ph el−1) in green polycrystalline perovskite LEDs. Our results provide a significant clue to develop effective CPAs for highly-efficient organic and perovskite LEDs.
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•Ideal conducting polymer anode with high work function and conductivity for high-efficiency perovskite LED is introduced.•Molecular scale control is introduced to decouple the work function with conductivity in a conducting polymer anode.•We achieved a high-efficiency polycrystalline perovskite LEDs with an external quantum efficiency of 10.93%.
Graphene is an optimal material to be employed as an ionic diffusion barrier because of its outstanding impermeability and chemical robustness. Indium tin oxide (ITO) is often used in perovskite ...light-emitting diodes (PeLEDs), and it can release indium easily upon exposure to the acidic hole-injection layer so that luminescence can be quenched significantly. Here, we exploit the outstanding impermeability of graphene and use it as a chemical barrier to block the etching that can occur in ITO exposed to an acidic hole-injection layer in PeLEDs. This barrier reduced the luminescence quenching that these metallic species can cause, so the photoluminescence lifetime of perovskite film was substantially higher in devices with ITO and graphene layer (87.9 ns) than in devices that had only an ITO anode (22.1 ns). Luminous current efficiency was also higher in PeLEDs with a graphene barrier (16.4 cd/A) than in those without graphene (9.02 cd/A). Our work demonstrates that graphene can be used as a barrier to reduce the degradation of transparent electrodes by chemical etching in optoelectronic devices.
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