Controlling the spatial distribution of quantum dots in nanofiber for light-harvesting devices

Abstract

The ability to control inter-dot or inter-molecule spacing of functional moieties in solid-state devices has long been studied for both fundamental and technological reasons. In this study, we present a new strategy for controlling the distance between quantum dots (QDs) based on one-dimensional spatial confinement in a polymer nanofiber template. This reliable technique allows for the isolation of QDs at a sufficient distance in a thin film and retains their monomeric character, with distinct spectra from aggregates (~30-nm shift) and monoexponential photoluminescence decay, indicating the suppression of inter-dot interactions. We successfully developed light-harvesting devices by incorporating QDs in nanofibers as an auxiliary light harvester, improving the performance of these devices from 5.9 to 7.4%. This strategy offers a viable path of controlling the arrangements of various functional moieties in solid-state devices. NPG Asia Materials (2015) 7, e202; doi:10.1038/am.2015.76; published online 17 July 2015 INTRODUCTIONThe physicochemical properties of functional moieties in devices such as organic dyes, quantum dots (QDs), graphenes and other nanostructures are different from the properties of their aggregates, 1-7 which frequently deteriorate the performance of the optoelectronic devices (light-emitting diodes, lasers, solar cells, waveguides or photosensors). [8][9][10][11][12][13][14] For instance, QD light-emitting diodes or photovoltaic devices suffer from the inter-dot interactions of aggregates, which cause a spectral shift and a broadening in the photoluminescence of QDs as well as a decrease in the quantum yield. 10,13 Therefore, control of inter-dot spacing is critical in ensuring device performance. [8][9][10]13,15 Researchers have long sought methods to control the spatial distribution of functional moieties in devices and prevent the formation of aggregates, both for fundamental research and the potential technological applications. In solid-state films in particular, it has been challenging to increase film thickness while keeping functional moieties in the monomeric state.Here, we demonstrate a general strategy for controlling the distance between functional moieties based on one-dimensional spatial confinement in a polymeric nanofiber template. One key observation, shown both experimentally and computationally, is that as the radius of a nanofiber template becomes smaller, the distance between moieties increases, thus leading to substantial isolation of each dot. QDs were chosen as a representative functional moiety because they can be easily observed by electron microscopy and because they have a high quantum yield, excellent photostability and long intrinsic lifetime that is distinguishable from their inter-dot energy transfer time (50 ps-2 ns). 15,16 We have fabricated isolated QDs (iQDs) by confining QDs

Enhanced Direct White Light Emission Efficiency in Quantum Dot Light‐Emitting Diodes via Embedded Ferroelectric Islands Structure

“…This resulted from the increased FRET process in the film state due to reduced distance between QDs. [ 23,27 ] As a result, a much higher volume of blue QDs were required than that of green and red QDs in the mixed QD solution for white light emission evidenced by the RGB mixing ratio 1:2:9, which is well consistent with previous reports that employed larger fraction of the QDs with higher bandgap than the QDs with lower bandgap. [ 19,23,28 ]…”

“…This resulted from the increased FRET process in the film state due to reduced distance between QDs. [23,27] As a result, a much higher volume of blue QDs were required than that of green and red QDs in the mixed QD solution for white light emission evidenced by the RGB mixing ratio 1:2:9, which is well consistent with previous reports that employed larger fraction of the QDs with higher bandgap than the QDs with lower bandgap. [19,23,28] For a ferroelectric layer, we employed ferroelectric polymer P(VDF-TrFE) due to the fascinating material properties of P(VDF-TrFE), such as chemical inertness, low fabrication temperatures, photostability, and its large electric polarization at even one nanometer thickness.…”

Tunable CsPb(Br/Cl)3perovskite nanocrystals and further advancement in designing light emitting fiber membranes

“…PMMA was chosen because its good spinnability, high stability, and potential towards surface modification. [49] Photophysical properties such as UV-Visible absorption, photoluminescence, and PLQY were investigated. To the authors knowledge this is the first-time report on CsPb(Br/Cl) 3 perovskite NCs luminescent fiber membranes synthesized by the centrifugal spinning technique.…”

Chemically resistant and thermally stable quantum dots prepared by shell encapsulation with cross-linkable block copolymer ligands

“…Homogeneous distribution of QDs in the matrix is a critical and basic requirement for solution-based devicefabrication processes, since massive aggregation of QDs causes poor reproducibility of the product, such as high haze and position-dependent optical quality. In addition, a close interparticle distance due to the aggregation of QDs promotes exciton transfer among QDs, which escalates the probability for photoexcited excitons to undergo nonradiative recombination processes 57,58 . To demonstrate the dispersion quality of the QDs in PMMA, composite films with OA-and P(MMA-b-XGMA)-QDs were prepared and characterized by TEM.…”