No abstract

There is an urgent demand to improve the efficiency and the color purity of the environment-friendly quantum dots (QDs), which can be used in wide color gamut (WCG) displays. In this study, we optimized the reaction conditions for the InP core synthesis and the ZnSe/ZnS multishell growth on the core. As a result, remarkable improvements were achieved in the photoluminescence quantum yield (PL QY, 95%) and the full width at half-maximum (fwhm, 36 nm), with perfectly matched wavelength (528 nm) for the green color in WCG displays. Injection of the phosphorus precursor at a mild temperature during the InP core synthesis reduced the size distribution of the core to 12%, and the shell growth performed at a high temperature significantly enhanced the crystallinity of the thick passivating layer. We also investigated the photophysical properties, particularly the energy trap distributions and trap state emissions of the InP-based QDs with different shell structures. The time-resolved and temperature-dependent PL spectra clearly indicated that the well-passivated InP/ZnSe/ZnS QDs showed nearly trap-free emissions over a wide temperature range (77–297 K). Also, the on- and off-time probability on single QD blinking and Auger ionization efficiencies also showed that these QDs were hardly affected by the surface traps.

Cesium-based perovskite nanocrystals (NCs) have outstanding photophysical properties improving the performances of lighting devices. Fundamental studies on excitonic properties and hot-carrier dynamics in perovskite NCs further suggest that these materials show higher efficiencies compared to the bulk form of perovskites. However, the relaxation rates and pathways of hot-carriers are still being elucidated. By using ultrafast transient spectroscopy and calculating electronic band structures, we investigated the dependence of halide in Cs-based perovskite (CsPbX with X=Br, I, or their mixtures) NCs on the hot-carrier relaxation processes. All samples exhibit ultrafast (<0.6 ps) hot-carrier relaxation dynamics with following order: CsPbBr (310 fs)>CsPbBr I (380 fs)>CsPbI NC (580 fs). These result accounts for a reduced light emission efficiency of CsPbI NC compared to CsPbBr NC.

low-cost processability. In particular, broad absorption range, large absorption coefficient, and high charge transport properties make them desirable for nextgeneration solar cell devices. [1,2] In fact, the highest solar cell efficiency for solution-processed devices reached over 20%, a record made by the perovskite based solar cells. [3] Recently, the organic-inorganic hybrid perovskites containing organic A-site cations were reported to exhibit enhanced two-photon absorption properties, [4] decelerated hot-carrier cooling, [5] and slower biexciton Auger recombination rate [6] compared to all-inorganic Cs-based perovskites. In addition, the highest efficiency perovskite solar cells reported to date all contain some fraction of organic A-cations. Since the exact role of organic species in the material's properties remains as open debate, the detailed exploration of the fundamental photophysics of the material will provide an important guideline for their potential applications.In addition to their bulk forms, perovskite nanostructures exhibit intriguing properties depending on their composition and architecture. Owing to their high quantum efficiency and broadly tunable electronic band gaps, perovskite quantum dots (PQDs) are under active investigation for their applications in lighting devices such as light-emitting diode displays and lasers. [7][8][9][10] The band gap energy of PQDs can easily be tuned to cover the entire visible spectral region by changing the halide species (Cl, Br, or I) or by controlling the size of PQDs. [11,12] Since nanostructures under quantum confinement effect are likely to experience significant size-dependent properties, [13] PQDs are also expected to exhibit distinct properties depending on their physical dimensions. While the size-dependent properties of all-inorganic PQDs have been investigated quite thoroughly, [14,15] the organic-inorganic hybrid PQDs remain relatively unexplored.In this sense, our approach was to obtain a comprehensive photophysical characterization of organic-inorganic hybrid PQDs of different sizes. We prepared CH 3 NH 3 PbBr 3 (MAPbBr 3 ) PQDs of three different sizes; PQD 1 (1.9 nm), PQD 2 (4.9 nm), and PQD 3 (9.6 nm) by controlling the precipitation temperature. [11] Based on the increasing photoluminescence Halide perovskites (ABX 3 ) have emerged as promising materials in the past decade owing to their superior photophysical properties, rendering them potential candidates as solar cells, light-emitting diode displays, and lasing materials. To optimize their utilization into optoelectronic devices, fundamental understanding of the optical behaviors is necessary. To reveal the comprehensive structure-property relationship, CH 3 NH 3 PbBr 3 (MAPbBr 3 ) perovskite quantum dots (PQDs) of three different sizes are prepared by controlling the precipitation temperature. Photoluminescence (PL) blinking, a key process that governs the emission efficiency of the PQD materials, is investigated in detail by the time-resolved spectroscopic measurements of individua...

To obtain highly efficient, stable, and environmentally friendly blue-light-emitting materials for display applications, we prepared a specially tailored Cd-free, colloidal quantum-well (CQW) structure of ZnS/ZnTeSe/ZnS. We optimized the synthetic methods to construct a very uniform ZnS core having a diameter of ∼2.9 nm within 10% of the size distribution. In addition, it was found that the ZnS QD structures were either a cube with the (100) surface facets or a tetrahedron with the (111) facets. As the ZnTeSe mid-shell grew on the ZnS core surface, the CQW maintained the initial facet and shape of the core. The photoluminescence of the CQW could be tuned from 375 to 458 nm by controlling the thickness of the ZnTeSe mid-shell. Furthermore, the spectral width changed depending on the Te composition in the ZnTeSe. After the final ZnS shell passivation, the optimized blue-light-emitting CQW showed a high quantum yield (QY) of up to 85% and a narrow spectrum width of 23 nm at 446 nm. Moreover, we fabricated light-emitting diodes (LEDs) with the CQW and demonstrated an external quantum efficiency of 6.8% at 3.6 V with a maximum brightness of 14 146 cd/m 2 at 8 V.