Enhanced emission directivity from asymmetrically strained colloidal quantum dots

Abstract

Current state-of-the-art quantum dot light-emitting diodes have reached close to unity internal quantum efficiency. Further improvement in external quantum efficiency requires more efficient photon out-coupling. Improving the directivity of the photon emission is considered to be the most feasible approach. Here, we report improved emission directivity from colloidal quantum dot films. By growing an asymmetric compressive shell, we are able to lift their band-edge state degeneracy, which leads to an overwhelming population of exciton with in-plane dipole moment, as desired for high-efficiency photon out-coupling. The in-plane dipole proportion determined by back-focal plane imaging method is 88%, remarkably higher than 70% obtained from conventional hydrostatically strained colloidal quantum dots. Enhanced emission directivity obtained here opens a path to increasing the external quantum efficiencies notably.

Simulations of nonradiative processes in semiconductor nanocrystals

“…These considerations have informed our development of the semiempirical pseudopotential model as a sufficiently detailed description of NCs that can also tackle calculations of experimentally relevant systems. For example, a CdSe quantum dot only 4 nm in diameter has over ∼1000 atoms and ∼4000 valence electrons, so the conventional workhorses of quantum chemistry, such as DFT and related methods for excited states, despite making significant progress, 68,69 are still far from being able to tackle this problem. On the other hand, continuum models based on the effective mass approximation have produced successful predictions for simple, linear spectroscopic observables 11 but are unable to capture many of the more complicated dynamic processes that determine the timescales of process like nonradiative exciton relaxation and AR.…”

“…II we describe the atomistic approach we have adopted to calculate quasiparticle excitations and neutral excitations in semiconductor NCs. First principles approaches, such as time-dependent density functional theory (DFT) [67][68][69] or many-body perturbation approximations, 70 are limited to describing excitons in relatively small clusters, typically those with fewer than 100 atoms, due to their steep computational scaling. 71,72 To make meaningful contact with experimental results on NCs that contain thousands of atoms and tens of thousands of electrons, we rely on the semiempirical pseudopotential model 9,25,26,73 to describe quasiparticle excitations.…”

Deep‐Red InP Core‐Multishell Quantum Dots for Highly Bright and Efficient Light‐Emitting Diodes

“…Colloidal quantum dots (QDs) are semiconductor nanostructures in which excitons are bounded in three dimensions. [1] They DOI: 10.1002/adom.202300612 have been widely used in light-emitting diodes (LEDs), [2][3][4][5][6] solar cells, [7,8] biomarkers, [9,10] lasers, and sensors [11] for their high photoluminescence quantum yield (PLQY), good monochromaticity, continuously adjustable emission wavelength, high stability, low preparation cost, and easy mass production. [12,13] Especially, quantumdot LED (QLED) is one of the most pursued technologies for next-generation display and lighting applications with both high energy efficiency and wide color gamut.…”

Wavelength-Dependent Spin Excitation with Circularly Polarized Light in CdSe Nanoplatelets

“…In 0D QDs, the band-edge HH and LH valence states are typically degenerate, preventing wavelength-selective excitation of either the HH exciton (HX) or LH exciton (LX) population and efficient injection of spin polarization with CPL. , This is seen in Figure b, where the optically bright HX and LX states with equal spin-angular momentum projections comprise electrons with anti-aligned spin projections. The large HH–LH splitting at the Γ point of 2D ZB CdSe NPLs facilitates selective excitation of either the HX or LX population with CPL by modulating the excitation wavelength.…”