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Density functional theory calculations are combined with time-resolved photoluminescence experiments to identify the species responsible for the reversible trapping of holes following photoexcitation of InP/ZnSe/ZnS core/shell/shell quantum dots (QDs) having excess indium in the shell [P. Cavanaugh et al., J. Chem. Phys. 155, 244705 (2021)]. Several possible assignments are considered, and a substitutional indium adjacent to a zinc vacancy, In3+/VZn 2-, is found to be the most likely. This assignment is consistent with the observation that trapping occurs only when the QD has excess indium and is supported by experiments showing that the addition of zinc oleate or acetate decreases the extent of trapping, presumably by filling some of the vacancy traps. We also show that the addition of alkyl carboxylic acids causes increased trapping, presumably by the creation of additional zinc vacancies. The calculations show that either a single In2+ ion or an In2+-In3+ dimer is much too easily oxidized to form the reversible traps observed experimentally, while In3+ is far too difficult to oxidize. Additional experimental data on InP/ZnSe/ZnS QDs synthesized in the absence of chloride demonstrates that the reversible traps are not associated with Cl-. However, a zinc vacancy adjacent to a substitutional indium is calculated to have its highest occupied orbitals about 1 eV above the top of the valence band of bulk ZnSe, in the appropriate energy range to act as reversible traps for quantum confined holes in the InP valence band. The associated orbitals are predominantly composed of p orbitals on the Se atoms adjacent to the Zn vacancy.

The nanoLED, an electroluminescent device utilizing quantum dots (QDs), is expected to be a promising candidate for the next‐generation display. This paper presents a newly developed QD protection technology for cadmium‐free nanoLEDs that enables simultaneous achievement of high‐efficiency electroluminescence (EL) and long lifetime. The device which was prototyped by applying ZnSeTe blue QDs to an emissive layer demonstrated a maximum external quantum efficiency (EQE) of 21.0% and a luminance half‐lifetime (LT50) of 128,000 hours at 100 nits. These results indicate that cadmium‐free nanoLEDs can meet the requirements for display application in terms of both EL efficiency and reliability. [ABSTRACT FROM AUTHOR]

Transient absorption (TA) and time-resolved photoluminescence (PL) spectroscopies have been used to elucidate the hole tunneling and Auger dynamics in biexcitons and negative trions in high-quality InP/ZnSe/ZnS quantum dots (QDs). In a previous paper [Nguyen et al., J. Phys. Chem. C 125, 15405–15414 (2021)], we showed that under high-intensity photoexcitation, two types of biexcitons are formed: those having two conduction band electrons and two valence band holes (designated as an XX state) and those having two conduction band electrons, one valence band hole, and an additional trapped hole (designated as an XT state). In the present paper, we show that both types of biexcitons can undergo Auger processes, with those of the XT state being a factor of four to five slower than those of the XX state. In addition, the trapped holes can undergo tunneling into the valence band, converting an XT state to an XX state. The relative amplitudes of the fast (XX) and slow (XT) components are different in the TA and PL kinetics, and these differences can be quantitatively understood in terms of oscillator strengths and electron–hole overlap integrals of each state. XT to XX hole tunneling rates are obtained from the comparison of the XT state lifetimes with those of the negative trions. This comparison shows that the tunneling times decrease with decreasing core size and shell thickness. These times are about 2 ns for the thinnest shell red-emitting QDs and decrease to 330 ps for QDs that luminesce in the yellow. [ABSTRACT FROM AUTHOR]

We have used time-correlated single photon counting to elucidate the radiative dynamics of InP/ZnSe/ZnS core/shell/shell quantum dots (QDs) that differ in the amount and distribution of excess indium. Stoichiometric QDs having an In:P atom ratio very near unity exhibit simple luminescence kinetics. The photoluminescence (PL) rises with the 40 ps instrument response function and exhibits a decay that is close to a single exponential with a time constant that decreases from 32 to 28 ns with increasing shell thickness. QDs having excess indium (In:P ratio of 1.15–1.63) show a significant component of a slower rise time assigned to transient population of indium-based hole traps in the ZnSe shell. They also have a slower PL decay, attributed to an equilibrium between these traps, which are optically dark, and the emissive valence-band state. This results in a radiative lifetime that increases from 32 to 48 ns with increasing shell thickness. Different treatments of the InP cores prior to shell deposition result in different core/shell interfaces as indicated by resonance Raman spectroscopy, as well as differences in the amplitude and timescale of the slow PL rise and the PL decay time. These are interpreted in terms of different radial distributions of the indium-based hole traps, which can be related to differences in the interfacial lattice strain. [ABSTRACT FROM AUTHOR]

Hexagonal p-type semiconductor CuS nanoplates were synthesized via a hot injection method from bis(trimethylsilyl)sulfide and the ionic liquid precursor bis(N-dodecylpyridinium) tetrachloridocuprate(ii). The particles have a broad size distribution with diameters between 30 and 680 nm and well-developed crystal habits. The nanoplates were successfully incorporated into organic photovoltaic (OPV) cells as hole conduction materials. The power conversion efficiency of OPV cells fabricated with the nanoplates is 16% higher than that of a control device fabricated without the nanoplates. [ABSTRACT FROM AUTHOR]

Because of outstanding optical properties and non-vacuum solution processability of colloidal quantum dot (QD) semiconductors, many researchers have developed various light emitting diodes (LEDs) using QD materials. Until now, the Cd-based QD-LEDs have shown excellent properties, but the eco-friendly QD semiconductors have attracted many attentions due to the environmental regulation. And, since there are many issues about the reliability of conventional QD-LEDs with organic charge transport layers, a stable charge transport layer in various conditions must be developed for this reason. This study proposes the organic/inorganic hybrid QD-LEDs with Cd-free InP QDs as light emitting layer and inorganic ZrO2 nanoparticles as electron transport layer. The QD-LED with bottom emission structure shows the luminescence of 530 cd m−2 and the current efficiency of 1 cd/A. To realize the transparent QD-LED display, the two-step sputtering process of indium zinc oxide (IZO) top electrode is applied to the devices and this study could fabricate the transparent QD-LED device with the transmittance of more than 74% for whole device array. And when the IZO top electrode with high work-function is applied to top transparent anode, the device could maintain the current efficiency within the driving voltage range without well-known roll-off phenomenon in QD-LED devices. [ABSTRACT FROM AUTHOR]

Semiconductor quantum dots (QDs) promise facile color tuning and high color saturation in quantum-dot light-emitting devices (QD-LEDs) by controlling nanoparticle size and size distribution. Here, we demonstrate how this promise can be practically realized for the cadmium-free InP/ZnSe/ ZnS multishell quantum dots. We developed a set of synthesis conditions and core/shell compositions that result in QDs with green, yellow, and red emission color. The QD-LEDs employing these QDs show efficient electroluminescence (EL) with luminance up to 1800 cd/m2 and efficiency up to 5.1 cd/A. The color coordinates calculated from the EL spectra clearly demonstrate the outstanding color saturation as an outcome of the narrow particle size distribution. These results prove that the performance gap between cadmium-free and cadmium-based QDs in QD-LEDs is shrinking rapidly. [ABSTRACT FROM AUTHOR]