Solvent‐Polarity‐Engineered Controllable Synthesis of Highly Fluorescent Cesium Lead Halide Perovskite Quantum Dots and Their Use in White Light‐Emitting Diodes

Abstract

wileyonlinelibrary.comBr, and I), have been intensively explored as promising photovoltaic materials and a respectable certified power conversion efficiency exceeding 22% has been achieved so far. [14] This great success has motivated research on perovskite QDs. [15] Among the various kinds of perovskites, all-inorganic lead halide perovskites, CsPbX 3 (X = Cl, Br, I), have demonstrated distinct photophysical properties, such as narrow emission line width, high quantum yield (QY) of luminescence, and short radiative lifetimes; they have thus been emerging as promising materials for applications like QD light-emitting diodes (LEDs), lasing and photodetectors. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] The current synthetic procedures of CsPbX 3 (X = Cl, Br, I) QDs can be mainly sorted into three routes, i.e., the direct ion reaction synthesis, anion-exchange synthesis, and the room-temperature reprecipitation. Kovalenko and co-workers pioneered the direct ion reaction synthesis of highly-luminescent CsPbX 3 (X = Cl, Br, I) nanocrystals in cubic perovskite structure using octadecene (ODE) at 140-200 °C; and through the compositional modulation and quantum size-effect, the emission could be tuned over the entire visible spectral region of 410-700 nm. [15] Following this approach, the anion-exchange method was successfully developed to prepare inorganic CsPbX 3 perovskite QDs, in which the reaction was initiated by adding another halide precursor into the parent CsPbX 3 QDs or mixing two kinds of parent QDs with different X component. [21,24] For the above two synthesis methods, CsPbX 3 QDs with good crystallinity and high yield could be obtained, but high temperature is often required to promote the reactions. At this point, room-temperature-based reprecipitation method was developed. [28,29,[33][34][35] Zeng and co-workers dissolved CsX and PbX 2 (X = Cl, Br, I) precursors in dimethylformamide (DMF) (or dimethylsulfoxide) together with oleylamine and oleic acid, then transferred the mixture to toluene, and obtained CsPbX 3 QDs at room temperature. [29] Deng and co-workers prepared the Cs-Oleate at 150 °C and by mixing the precursor with the DMF solution of PbX 2 , they synthesized various CsPbX 3 nanostructures (nanorods, nanocubes, nanoplates, and QDs) Cesium lead halide quantum dots (QDs) have tunable photoluminescence that is capable of covering the entire visible spectrum and have high quantum yields, which make them a new fluorescent materials for various applications. Here, the synthesis of CsPbX 3 (X = Cl, Br, I, or mixed Cl/Br and Br/I) QDs by direct ion reactions in ether solvents is reported, and for the first time the synergetic effects of solvent polarity and reaction temperature on the nucleation and growth of QDs are demonstrated. The use of solvent with a low polarity enables controlled growth of QDs, which facilitates the synthesis of high-quality CsPbX 3 QDs with broadly tunable luminescence, narrow emission width, and high quantum yield. A QD white LED (WLED) is demon...

Fully‐Inorganic Trihalide Perovskite Nanocrystals: A New Research Frontier of Optoelectronic Materials

“…[22] As illustrated in Equation (1), the formation reaction of CsPbX 3 NCs is conducted with excess halide, and cesium oleate is the 1) complicated experimental device. [83] Consequently, the reaction medium is also a key parameter to the hot-injection synthesis of CsPbX 3 NCs. [80] www.advmat.de www.advancedsciencenews.com limiting reagent.…”

Perovskite Quantum Dots and Their Application in Light‐Emitting Diodes

“…Thus far, synthesis methods for PQD comprise many types. Nucleation growth mechanism of PQDs can be separated into LaMer nucleation and oriented attachment growth mechanism . During LaMer nucleation and growth mechanism, QDs exhibit low critical size for nucleation at high temperatures; this property prevents nuclei from transforming into large crystals .…”

“…In nanocrystal synthesis, oleic acid (OA) plays a key role in growth orientation of nanoparticles and self‐assembly of CsPbBr 3 nanosheets. Li et al explained synthesis mechanism of CsPbBr 3 QDs in low‐polarity solvents. As depicted in Figure , intermediate products form based on LaMer nucleation.…”

“…Growth processes of CsPbBr 3 QDs with low‐polarity solvents at different temperatures (Reproduced with permission . Copyright 2016, Wiley‐VCH).…”

“…Figure a–c displays electroluminescence (EL) spectra, photographs, and chromaticity coordinates, respectively, in CIE diagrams with and without red CsPb(Br/I) 3 PQD device. Li et al fabricated CsPbBr 3 PQDs with red (Ba, Ca, Sr) 3 SiO 5 :Eu (BCS) phosphors in homogeneous epoxy silicon and then cured the material in vacuum oven at 40 °C for 60 min and at 150 °C for 1 h. The fabricated white‐light LEDs yielded a CRI value of 93.2 and CCT of 5447 K at 20 mA current. This device showed excellent color rendering properties even after storage in ambient environment for 1 month.…”