Holistic Determination of Optoelectronic Properties using High-Throughput Spectroscopy of Surface-Guided CsPbBr3 Nanowires

Abstract

Optoelectronic micro- and nanostructures have a vast parameter space to explore for modification and optimization of their functional performance. This paper reports on a data-led approach using high-throughput single nanostructure spectroscopy to probe >8000 structures, allowing for holistic analysis of multiple material and optoelectronic parameters with statistical confidence. The methodology is applied to surface-guided CsPbBr 3 nanowires, which have complex and interrelated geometric, structural, and electronic properties. Photoluminescence-based measurements, studying both the surface and embedded interfaces, exploits the natural inter nanowire geometric variation to show that increasing the nanowire width reduces the optical bandgap, increases the recombination rate in the nanowire bulk, and reduces the rate at the surface interface. A model of carrier recombination and diffusion ascribes these trends to carrier density and strain effects at the interfaces and self-consistently retrieves values for carrier mobility, trap densities, bandgap, diffusion length, and internal quantum efficiency. The model predicts parameter trends, such as the variation of internal quantum efficiency with width, which is confirmed by experimental verification. As this approach requires minimal a priori information, it is widely applicable to nano- and microscale materials.

Improving Quantum Well Tube Homogeneity Using Strained Nanowire Heterostructures

“…PL spectra for each structure were fit with a Lasher–Stern–Würfel (LSW) model as detailed in the Supporting Information. , Briefly, the LSW model is comprised of a two-dimensional density of states model ( K ( E )) modified with the addition of an Urbach tail ( U ( E )) to account for low-energy band edge variations often observed in disordered materials, , and convoluted with a Gaussian ( G ( E )) to represent the system resolution, and was given by I normalL normalS normalW ( E ) = A 1 G ( E ) ⊗ { lefttrue false[ A 2 U ( E , L , γ ) false] , when E ≤ E g false[ K ( E , E well , E f , T ) false] , when E > E g where E is the photon energy, E f is the Fermi energy, T is the effective emission temperature, E well is the quantum-well transition energy, γ is the Urbach energy, and A 1,2 are scaling factors. An example of a fit is given in Figure b.…”

“…PL spectra for each structure were fit with a Lasher−Stern− Wurfel (LSW) model as detailed in the Supporting Information. 33,34 Briefly, the LSW model is comprised of a two-dimensional density of states model (K(E)) modified with the addition of an Urbach tail (U(E)) to account for low-energy band edge variations often observed in disordered materials, 21,35 and convoluted with a Gaussian (G(E)) to represent the system resolution, and was given by…”

“…The relative impact of material inhomogeneity and disorder increases significantly toward nanometer fabrication scales; , when considering heterostructures, such as QWs, even monolayer thickness variations can lead to significant shifts in their emission range . As such, tight control of local growth conditions is considered essential − which is particularly difficult for bottom-up grown materials at the wafer-scale.…”

“…In QW systems, intramaterial strain improves carrier confinement 18 and radiative efficiency 19 at room temperature, which is particularly important for nanolasers at telecommunication wavelengths. 1 The relative impact of material inhomogeneity and disorder increases significantly toward nanometer fabrication scales; 20,21 when considering heterostructures, such as QWs, even monolayer thickness variations can lead to significant shifts in their emission range. 22 As such, tight control of local growth conditions is considered essential 23−26 which is particularly difficult for bottom-up grown materials at the wafer-scale.…”

Sub-Picosecond Carrier Dynamics Explored using Automated High-Throughput Studies of Doping Inhomogeneity within a Bayesian Framework

“…A set of 20,000 NWs were initially located and investigated using automated micro-photoluminescence (µ-PL) spectroscopy. 38 A continuous-wave HeNe laser of 632.8 nm wavelength with circular polarisation (to avoid polarisation dependant absorption effects 39 ) and power density at the sample of 6.4 kW cm −2 was used (equivalent to around 30 photons/picosecond/NW). Photoluminescence (PL) spectra and dark-field optical images were collected for each NW; the approximate length of each NW was extracted from the images.…”