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Efficient Single‐Layer Polymer Light‐Emitting Diodes
Kabra, Dinesh,Lu, Li Ping,Song, Myoung Hoon,Snaith, Henry J.,Friend, Richard H. WILEY‐VCH Verlag 2010 Advanced Materials Vol.22 No.29
<P><B>Single‐layer polymer light‐emitting diodes</B> are fabricated using poly (9,9′‐dioctylfluorene)‐<I>co</I>‐ benzothiadiazole (F8BT) as the emissive layer in contact with metal oxide injection layers ITO/ZnO/Cs<SUB>2</SUB>CO<SUB>3</SUB>/F8BT/MoO<SUB>3</SUB>/Au. Luminous efficiencies of up to 23 cd A<SUP>−1</SUP> are achieved for polymer layer thicknesses near 1 <I>μ</I>m. </P>
High-Efficiency Polycrystalline Perovskite Light-Emitting Diodes Based on Mixed Cations
Cho, Himchan,Kim, Joo Sung,Wolf, Christoph,Kim, Young-Hoon,Yun, Hyung Joong,Jeong, Su-Hun,Sadhanala, Aditya,Venugopalan, Vijay,Choi, Jin Woo,Lee, Chang-Lyoul,Friend, Richard H.,Lee, Tae-Woo American Chemical Society 2018 ACS NANO Vol.12 No.3
<P>We have achieved high-efficiency polycrystalline perovskite light-emitting diodes (PeLEDs) based on formamidinium (FA) and cesium (Cs) mixed cations without quantum dot synthesis. Uniform single-phase FA<SUB>1-<I>x</I></SUB>Cs<SUB><I>x</I></SUB>PbBr<SUB>3</SUB> polycrystalline films were fabricated by one-step formation with various FA:Cs molar proportions; then the influences of chemical composition on film morphology, crystal structure, photoluminescence (PL), and electroluminescence (EL) were systematically investigated. Incorporation of Cs<SUP>+</SUP> cations in FAPbBr<SUB>3</SUB> significantly reduced the average grain size (to 199 nm for FA:Cs = 90:10) and trap density; these changes consequently increased PL quantum efficiency (PLQE) and PL lifetime of FA<SUB>1-<I>x</I></SUB>Cs<SUB><I>x</I></SUB>PbBr<SUB>3</SUB> films and current efficiency (CE) of PeLEDs. Further increase in Cs molar proportion from 10 mol % decreased crystallinity and purity, increased trap density, and correspondingly decreased PLQE, PL lifetime, and CE. Incorporation of Cs also increased photostability of FA<SUB>1-<I>x</I></SUB>Cs<SUB><I>x</I></SUB>PbBr<SUB>3</SUB> films, possibly due to suppressed formation of light-induced metastable states. FA<SUB>1-<I>x</I></SUB>Cs<SUB><I>x</I></SUB>PbBr<SUB>3</SUB> PeLEDs show the maximum CE = 14.5 cd A<SUP>-1</SUP> at FA:Cs = 90:10 with very narrow EL spectral width (21-24 nm); this is the highest CE among FA-Cs-based PeLEDs reported to date. This work provides an understanding of the influences of Cs incorporation on the chemical, structural, and luminescent properties of FAPbBr<SUB>3</SUB> polycrystalline films and a breakthrough to increase the efficiency of FA<SUB>1-<I>x</I></SUB>Cs<SUB><I>x</I></SUB>PbBr<SUB>3</SUB> PeLEDs.</P> [FIG OMISSION]</BR>
Hassan, Yasser,Ashton, Olivia J.,Park, Jong Hyun,Li, Guangru,Sakai, Nobuya,Wenger, Bernard,Haghighirad, Amir-Abbas,Noel, Nakita K.,Song, Myoung Hoon,Lee, Bo Ram,Friend, Richard H.,Snaith, Henry J. American Chemical Society 2019 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.141 No.3
<P>Metal halide perovskites are promising candidates for use in light emitting diodes (LEDs), due to their potential for color tunable and high luminescence efficiency. While recent advances in perovskite-based light emitting diodes have resulted in external quantum efficiencies exceeding 12.4% for the green emitters, and infrared emitters based on 3<I>D</I>/2D mixed dimensional perovskites have exceeded 20%, the external quantum efficiencies of the red and blue emitters still lag behind. A critical issue to date is creating highly emissive and stable perovskite emitters with the desirable emission band gap to achieve full-color displays and white LEDs. Herein, we report the preparation and characterization of a highly luminescent and stable suspension of cubic-shaped methylammonium lead triiodide (CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>) perovskite nanocrystals, where we synthesize the nanocrystals via a ligand-assisted reprecipitation technique, using an acetonitrile/methylamine compound solvent system to solvate the ions and toluene as the antisolvent to induce crystallization. Through tuning the ratio of the ligands, the ligand to toluene ratio, and the temperature of the toluene, we obtain a solution of CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB> nanocrystals with a photoluminescence quantum yield exceeding 93% and tunable emission between 660 and 705 nm. We also achieved red emission at 635 nm by blending the nanocrystals with bromide salt and obtained perovskite-based light emitting diodes with maximum electroluminescent external quantum efficiency of 2.75%.</P> [FIG OMISSION]</BR>
Lu, Li Ping,Finlayson, Chris E.,Kabra, Dinesh,Albert‐,Seifried, Sebastian,Song, Myoung Hoon,Havenith, Remco W. A.,Tu, Guoli,Huck, Wilhelm T. S.,Friend, Richard H. WILEY‐VCH Verlag 2013 Macromolecular chemistry and physics Vol.214 No.9
<P><B>Abstract</B></P><P>A study of the organic semiconductor F8TBT is presented, directly comparing a conventional form (F8TBT‐out) with a form with varied alkyl side‐chain position (F8TBT‐in), in terms of optical properties and device performance in light‐emitting‐diodes (LEDs). Computational simulations of the side‐chain position with respect to the TBT unit reveal geometrical differences between F8TBT‐out and F8TBT‐in. π–π conjugation on the backbone of F8TBT‐in is interrupted by a distortion of the benzothiadiazole ring, leading to a blue‐shift of the absorption spectrum and increased photoluminescence quantum efficiency. Both conventional and hybrid LEDs demonstrate that devices with F8TBT‐in show improved performance, as compared to F8TBT‐out, illustrating how tuning the optoelectronic properties of conjugated polymers by varying the placement of side chains has an important role in device optimization.</P>
Kim, Young-Hoon,Wolf, Christoph,Kim, Young-Tae,Cho, Himchan,Kwon, Woosung,Do, Sungan,Sadhanala, Aditya,Park, Chan Gyung,Rhee, Shi-Woo,Im, Sang Hyuk,Friend, Richard H.,Lee, Tae-Woo American Chemical Society 2017 ACS NANO Vol.11 No.7
<P>Colloidal metal-halide perovskite quantum dots (QDs) with a dimension less than the exciton Bohr diameter D-B (quantum size regime) emerged as promising light emitters due to their spectrally narrow light, facile color tuning, and high photoluminescence quantum efficiency (PLQE). However, their size-sensitive emission wavelength and color purity and low electroluminescence efficiency are still challenging aspects. Here, we demonstrate highly efficient light-emitting diodes (LEDs) based on the colloidal perovskite nano crystals (NCs) in a dimension > D-B (regime beyond quantum size) by using a multifunctional buffer hole injection layer (Buf-HIL). The perovskite NCs with a dimension greater than D-B show a size-irrespective high color purity and PLQE by managing the recombination of excitons occurring at surface traps and inside the NCs. The Buf-HIL composed of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and per fluorinated ionomer induces uniform perovskite particle films with complete film coverage and prevents exciton quenching at the PEDOT:PSS/perovskite particle film interface. With these strategies, we achieved a very high PLQE (similar to 60.5%) in compact perovskite particle films without any complex post-treatments and multilayers and a high current efficiency of 15.5 cd/A in the LEDs of colloidal perovskite NCs, even in a simplified structure, which is the highest efficiency to date in green LEDs that use colloidal organic-inorganic metal-halide perovskite nanoparticles including perovskite QDs and NCs. These results can help to guide development of various light-emitting optoelectronic applications based on perovskite NCs.</P>
Growth of Nanosized Single Crystals for Efficient Perovskite Light-Emitting Diodes
Lee, Seungjin,Park, Jong Hyun,Nam, Yun Seok,Lee, Bo Ram,Zhao, Baodan,Di Nuzzo, Daniele,Jung, Eui Dae,Jeon, Hansol,Kim, Ju-Young,Jeong, Hu Young,Friend, Richard H.,Song, Myoung Hoon American Chemical Society 2018 ACS NANO Vol.12 No.4
<P>Organic-inorganic hybrid perovskites are emerging as promising emitting materials due to their narrow full-width at half-maximum emissions, color tunability, and high photoluminescence quantum yields (PLQYs). However, the thermal generation of free charges at room temperature results in a low radiative recombination rate and an excitation-intensity-dependent PLQY, which is associated with the trap density. Here, we report perovskite films composed of uniform nanosized single crystals (average diameter = 31.7 nm) produced by introducing bulky amine ligands and performing the growth at a lower temperature. By effectively controlling the crystal growth, we maximized the radiative bimolecular recombination yield by reducing the trap density and spatially confining the charges. Finally, highly bright and efficient green emissive perovskite light-emitting diodes that do not suffer from electroluminescence blinking were achieved with a luminance of up to 55 400 cd m<SUP>-2</SUP>, current efficiency of 55.2 cd A<SUP>-1</SUP>, and external quantum efficiency of 12.1%.</P> [FIG OMISSION]</BR>