Near-Unity Photoluminescence Quantum Yield of Core-Only InP Quantum Dots via a Simple Postsynthetic InF3 Treatment

Indium phosphide (InP) quantum dots (QDs) are considered the most promising alternative for Cd and Pb-based QDs for lighting and display applications. However, while core-only QDs of CdSe and CdTe have been prepared with near-unity photoluminescence quantum yield (PLQY), this is not yet achieved for InP QDs. Treatments with HF have been used to boost the PLQY of InP core-only QDs up to 85%. However, HF etches the QDs, causing loss of material and broadening of the optical features. Here, we present a simple postsynthesis HF-free treatment that is based on passivating the surface of the InP QDs with InF3. For optimized conditions, this results in a PLQY as high as 93% and nearly monoexponential photoluminescence decay. Etching of the particle surface is entirely avoided if the treatment is performed under stringent acid-free conditions. We show that this treatment is applicable to InP QDs with various sizes and InP QDs obtained via different synthesis routes. The optical properties of the resulting core-only InP QDs are on par with InP/ZnSe/ZnS core-shell QDs, with significantly higher absorption coefficients in the blue, and with potential for faster charge transport. These are important advantages when considering InP QDs for use in micro-LEDs or photodetectors.

Near-Unity Emitting, Widely Tailorable, and Stable Exciton Concentrators Built from Doubly Gradient 2D Semiconductor Nanoplatelets

The strength of electrostatic interactions (EIs) between electrons and holes within semiconductor nanocrystals profoundly affects the performance of their optoelectronic systems, and different optoelectronic devices demand distinct EI strength of the active medium. However, achieving a broad range and fine-tuning of the EI strength for specific optoelectronic applications is a daunting challenge, especially in quasi two-dimensional core-shell semiconductor nanoplatelets (NPLs), as the epitaxial growth of the inorganic shell along the direction of the thickness that solely contributes to the quantum confined effect significantly undermines the strength of the EI. Herein we propose and demonstrate a doubly gradient (DG) core-shell architecture of semiconductor NPLs for on-demand tailoring of the EI strength by controlling the localized exciton concentration via in-plane architectural modulation, demonstrated by a wide tuning of radiative recombination rate and exciton binding energy. Moreover, these exciton-concentration-engineered DG NPLs also exhibit a near-unity quantum yield, high photo- and thermal stability, and considerably suppressed self-absorption. As proof-of-concept demonstrations, highly efficient color converters and high-performance light-emitting diodes (external quantum efficiency: 16.9%, maximum luminance: 43,000 cd/m2) have been achieved based on the DG NPLs. This work thus provides insights into the development of high-performance colloidal optoelectronic device applications.

Facet-Defect Tolerant Bi-Doped Cs2AgxNa1-xInCl6 Nanoplatelets with a Near-Unity Photoluminescence Quantum Yield

We report the colloidal synthesis of Bi-doped Cs2AgxNa1-xInCl6 double perovskite nanoplatelets (NPLs) exhibiting a near-unity photoluminescence quantum yield (PLQY), a record emission efficiency for nanoscale lead-free metal halides. A combination of optical spectroscopies revealed that nonradiative decay processes in the NPL were suppressed, indicating a well-passivated surface. By comparison, nanocubes with the same composition and surface ligands as the NPLs had a PLQY of only 40%. According to our calculations, the type of trap states arising from the presence of surface defects depends on their specific location: defects located on the facets of nanocubes generate only shallow traps, while those at the edges result in deep traps. In NPLs, due to their extended basal facets, most of the surface defects are facet defects. This so-called facet-defect tolerant behavior of double perovskites explains the more efficient optical emission of NPLs compared to that of nanocubes.

Mn-Doped Multiple Quantum Well Perovskites for Efficient Large-Area Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) can be used as large-area sunlight collectors, which show great potential in the application of building-integrated photovoltaic areas. Achieving highly efficient LSCs requires the suppression of reabsorption losses while maintaining a high photoluminescence quantum yield (PLQY) and broad absorption. Perovskites as the superstar fluorophores have recently emerged as candidates for large-area LSCs. However, highly emissive perovskites with a large Stokes shift and broad absorption have not been obtained up to now. Here, we devised a facile synthetic route to obtain Mn-doped multiple quantum well (MQW) Br-based perovskites. The Br-based perovskite host ensures broad absorption. Efficient energy transfer from the exciton to the Mn dopant produces a large Stokes shift and high PLQY simultaneously. By further coating the perovskites with Al₂O₃, the stability and PLQY are greatly elevated. A large area of liquid LSC (40 cm × 40 cm × 0.5 cm) is fabricated, which possesses an internal quantum efficiency (η_int) of 47% and an optical conversion efficiency (η_opt) reaching 11 ± 1%, which shows the highest value for large-area LSCs.