CsPbX3 (X = I, Br, Cl) perovskite nanocrystals (NCs)
have recently emerged as emitting materials for optoelectronic and
display applications owing to their easily tunable emissions, high
photoluminescence quantum yield (PLQY), and vivid color purity (full
width at half maximum of approximately 20 nm). However, the lagging
quantum yields of blue-emitting perovskite NCs have resulted in low
efficiency compared to green or red perovskite light-emitting diodes
(PeLEDs); moreover, the long insulating ligands (such as oleylamine
and oleic acid) inhibit charge carrier injection. In this study, we
demonstrated a facile ligand-mediated post-treatment (LMPT) method
for high-quality perovskite NCs with changing optical properties to
allow fine-tuning of the target emission wavelength. This method involves
the use of a mixed halide ion-pair ligand, di-dodecyl dimethyl ammonium
bromide, and chloride, which can induce a reconstruction through a
self-anion exchange. Using the LMPT method, the PLQY of the surface-passivated
blue-emitting NCs was dramatically enhanced to over 70% within the
485 nm blue emission region and 50% within the 467 nm deep-blue emission
region. Through this treatment, we achieved highly efficient blue-PeLED
maximum external quantum efficiencies of 0.44 and 0.86% within the
470 and 480 ± 2 nm electroluminescence emission regions, respectively.
To date, the light emitting diode (LED) based halide perovskite was rapidly developed due to the outstanding property of perovskite materials. However, the blue perovskite LEDs based on the bulk halide perovskites have been rarely researched and showed low efficiencies. The bulk blue perovskite LEDs suffered from insufficient coverage on the substrate due to the low solubility of the inorganic Cl sources or damaged by the structural instability with participation of organic cations. Here, we show the new method of fabricating stable inorganic bulk blue perovskite LEDs with the anion exchange approach to avoid use of insoluble Cl precursors. The devices showed nice operational spectral stability at the desired blue emission peak. The bulk perovskite blue LEDs showed a maximum luminance of 1468 and 494 cd m −2 for the 490 and 470 nm emission peaks, respectively.
A fully reversible (CsPbCl 3 # CsPbBr 3 # CsPbI 3) post-treatment method of anion exchange for CsPbX 3 (X = Cl, Br, I) perovskite nanocrystals conducted with haloalkane solvent and nucleophile is presented. Through the control of anionexchange kinetics, the band gaps of nanocrystals are finely tuned covering the full wavelength region from 400 to 700 nm. The dissociation mechanism of haloalkane solvent with nucleophile is clearly explained with S N 2 chemical reaction to produce halide anions. With the post-treatment method, fabricated LED devices showed highly saturated RGB colors.
The all-inorganic perovskite CsPbI3 has emerged as an alternative photovoltaic material to organic–inorganic hybrid perovskites due to its non-volatile composition and comparable photovoltaic performance.
Nickel oxide (NiO) offers intrinsic p‐type behavior and high thermal and chemical stability, making it promising as a hole transport layer (HTL) material in inverted organic solar cells. However, its use in this application has been rare because of a wettability problem caused by use of water as base solvent and high‐temperature annealing requirements. In the present work, an annealing‐free solution‐processable method for NiO deposition is developed and applied in both conventional and inverted non‐fullerene polymer solar cells. To overcome the wettability problem, the typical DI water solvent is replaced with a mixed solvent of DI water and isopropyl alcohol with a small amount of 2‐butanol additive. This allows a NiO nanoparticle suspension (s‐NiO) to be deposited on a hydrophobic active layer surface. An inverted non‐fullerene solar cell based on a blend of p‐type polymer PTB7‐Th and non‐fullerene acceptor IEICO‐4F exhibits the high efficiency of 11.23% with an s‐NiO HTL, comparable to the efficiency of an inverted solar cell with a MoOx HTL deposited by thermal evaporation. Conventionally structured devices including this s‐NiO layer show efficiency comparable to that of a conventional device with a PEDOT:PSS HTL.
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