Photoinduced Carrier Dynamics of Nearly Stoichiometric Oleylamine-Protected Copper Indium Sulfide Nanoparticles and Nanodisks

Abstract

Copper indium sulfide (CuInS 2 ) nanocrystals (NCs) are nontoxic and cost-effective, making them attractive for use in highly efficient solar cells. However, direct observations of the photoinduced carrier dynamics of CuInS 2 NCs to examine the relationship between carrier dynamics and structural parameters with the aim of optimizing NC properties for specific applications are limited. Here, we synthesized nearly stoichiometric oleylamine-protected CuInS 2 NCs using two convenient onepot methods to produce CuInS 2 nanoparticles and nanodisks. Transient absorption measurements using femtosecond laser flash photolysis revealed that the use of oleylamine as a protecting ligand leads to the formation of vacancy-doped NCs. The rapid decay of the photogenerated excitons in the oleylamine-protected NCs was not sensitive to the crystal structure or shape of NCs, and could be explained by defect trapping and energy transfer to the hole-based localized surface plasmon resonance in the oleylamine-protected NCs. Our results confirm that careful selection of a protecting ligand is important to obtain CuInS 2 NCs with optimized properties for particular applications.

Radiative and Nonradiative Recombination in CuInS2 Nanocrystals and CuInS2-Based Core/Shell Nanocrystals

“…A negative signal (i.e., a photoinduced reduction in absorption) appears at around 530 nm, at the same wavelength as the shoulder in the steady-state absorption spectrum (Figure A and SI, Figure S7). This signal is therefore assigned to the band edge bleach, in agreement with previous reports. ,,− In the infrared (700–1600 nm), a broad positive signal is observed. We assign this to excited-state absorption and will discuss its possible nature in more detail below.…”

Ternary Metal Chalcogenides: Into the Exciton and Biexciton Dynamics

“…51−53 Apparently, a manifold of In−Cu related electronic states exists above the CB, and electron cooling involving these states results in shifting and broadening of the bleach spectrum. 54 Herein, the blue-shifted bleach spectra at very early time delay (<1 ps) were due to the electron population in the upper electronic states in the manifold state rather than the CB edge. Because the degree of confinement in the CIS NCs was found to be much less in comparison to that of the common II−VI NCs, the electrons can be populated in the extensive range of the gradient states above the CB.…”

“…While most studied II–VI and III–V NCs show narrow and structured bleach at the excited state due to different confined (1S, 2S, 1P, etc.) electronic states, the observation of such a structureless bleach indicates the absence of a well-confined excited state and involves multiple excited electronic states. − Apparently, a manifold of In–Cu related electronic states exists above the CB, and electron cooling involving these states results in shifting and broadening of the bleach spectrum . Herein, the blue-shifted bleach spectra at very early time delay (<1 ps) were due to the electron population in the upper electronic states in the manifold state rather than the CB edge.…”

Investigation of the size–property relationship in CuInS2quantum dots

“…Furthermore, the FWHM of fraction #2 is narrower, which may result from the fact that a smaller range of particle sizes is contributing to the emission. The emission properties of multicomponent QDs have been investigated in the past [60][61][62][63] with a focus on the underlying recombination mechanisms. The position of the emission signal in CuInS 2 -based systems has been attributed to donor-acceptor pair (DAP) recombinations on the surface (higher energy) or inside the particles (lower energy).…”