Colloidal Quantum Shells: An Emerging 2D Semiconductor for Energy Applications

Abstract

Low-dimensional semiconductors hold strong promise for future energy applications. These nanomaterials are inexpensive to process and offer a broad spectrum of attractive quantum-mechanical properties. The notorious problem of low-dimensional nanostructures, however, lies in their limited performance under high energetic loads when more than one exciton per particle is created. Multiple excitons undergo fast annihilation, causing efficient roll-off in energy-intensive applications, including high-brightness light-emitting diodes, X-ray scintillators, and solar cells. In this Focus Review, we highlight an emerging type of low-dimensional semiconductors that make it possible to avoid such multiexciton (MX) energy losses. Recently demonstrated colloidal quantum shells benefit from the spatial separation of multiple excitons, which leads to extraordinary improvements to MX lifetimes and MX quantum yield. This makes the quantum shell morphology attractive for solution-processed optical and electrical devices. Here, we compare the optoelectronic properties of quantum shells against other low-dimensional semiconductors and discuss their emerging opportunities in solid-state lighting and energy-harvesting applications.

CdS/CdSe/CdS Spherical Quantum Wells with Near-Unity Biexciton Quantum Yield for Light-Emitting-Device Applications

“…Figure 4d shows calculated BX Auger lifetimes as predicted by the scaling model for QSs with different radii. 27 Here, the effect of QS geometry on Auger lifetimes was estimated by assuming a superlinear scaling of τ Auger with the exciton volume τ Auger ≈ V 1.1 . Such volume scaling is based on the interacting formalism 44 that accurately describes Coulomb coupling between the initial and final multicharge states in large-size nanostructures and, therefore, applies to the quantum shell geometry.…”

“…To alleviate the above issues of NPLs, we have recently developed a quasi-two-dimensional, spherical CQW nanoscale geometry comprising a CdSe quantum-confined spherical shell sandwiched between a wider-band-gap CdS core and CdS outer layersa quantum shell (QS) geometry. − Here, the separation of charge carriers is defined not only by the mutual attraction or repulsion of the X pairs but also by the core size (Figure ). It is expected that the QS geometry strongly suppresses MX Auger rates and leads to improved performance due to the increased volume available to multiple excitons.…”

Reasoning the Photoluminescence Blinking in CdSe–CdS Heteronanostructures as Stacking Fault-Based Trap States

“…More importantly, the tunable optoelectronic properties of semiconductor systems, due to quantum confinement effects, offer numerous possible applications (e.g., display devices, light-harvesting systems, and so on). − Nonetheless, their performance is greatly affected by the additional nonradiative channels because of the presence of midband gap states (trap states) . These states can trap photogenerated electrons/holes, thus preventing excitons from band edge recombination. − The density of trap states formed due to the dangling bonds on the surface can be reduced by overcoating with another inorganic semiconductor material as a shell since it offers robustness and additional possibilities of carrier wave function engineering. − However, the choice of semiconductor material for surface passivation and their crystallinity are crucial in designing heteronanostructures.…”

Accelerated Multi‐Stage Synthesis of Indium Phosphide Quantum Dots in Modular Flow Reactors

“…Quantum dots (QDs) have been established as an ideal class of optical materials for a wide range of applications in energy, chemical, and healthcare industries, including bioimaging, [1] solar cells, [2] luminescence solar concentrators, [3,4] displays, [5,6] solid-state lighting, [7] light-emitting-diodes (LEDs), [8,9] and photocatalysis. [10,11] The growth in popularity of QDs has been driven by their unique optical and electronic properties that can be precisely tuned by controlling their size, morphology, and composition.…”