Composition and Size-Dependent Extinction Coefficient of Colloidal PbSe Quantum Dots

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS) was combined with UV–vis−NIR spectrophotometry and transmission electron microscopy to determine the nanocrystal composition and molar extinction coefficient ϵ of colloidal PbSe quantum dot (Q-PbSe) suspensions. The ICP-MS results show a nonstoichiometric Pb/Se ratio, with a systematic excess of lead for all samples studied. The observed ratio is consistent with a faceted spherical Q-PbSe model, composed of a quasi stoichiometric Q-PbSe core terminated by a Pb surface shell. At high photon energies, we find that ϵ scales with the nanocrystal volume, irrespective of the Q-PbSe size. From ϵ, we calculated a size-independent absorption coefficient. Its value is in good agreement with the theoretical value for bulk PbSe. At the band gap, ϵ is size-dependent. The resulting absorption coefficient increases quadratically with decreasing Q-PbSe size. Calculations of the oscillator strength of the first optical transition are in good agreement with theoretical tight binding calculations, showing that the oscillator strength increases linearly with Q-PbSe size.

Size-Dependent Optical Properties of Colloidal PbS Quantum Dots

“…Both predict an E 0 scaling mainly with d Ϫ1 . This is similar to the size dependence of E 0 for PbSe Qdots, 16,21 albeit that PbS Qdots are typically larger than PbSe Qdots for a given E 0 . Note that, although we have not synthesized particles with a size below 3.5 nm, the extrapolation of the sizing curve still agrees well with calculated data of Kane et al 25 Assessment of the Sample Purity.…”

“…To confirm that the suspensions are free of sulfurbased precursors (oleylamineϪsulfur complexes, OLA-S, and/or tri-n-octylphosphine sulfide, TOPS), PbS Qdots are suspended in deuterated toluene (toluened 8 ) and a quantitative proton nuclear magnetic resonance ( 1 H NMR) spectrum is measured. 16,27 Figure 3b shows that, apart from a sharp singlet due to dibromomethane (CH 2 Br 2 , 3.94 ppm, OE), a quintuplet due to residual toluene (2.09 ppm, ▫) and a singlet possibly due to methanol (2.12 ppm, o), no sharp signals arising from OLA-S and/or TOPS are observed. The broad resonances in fact arise from oleic acid (OA) ligands bound to the PbS Qdot surface.…”

“…22,23 In this paper, we apply the methods derived previously 16 to calculate the optical properties of colloidal PbS Qdots. First, the PbS Qdot concentration c 0 is carefully determined by elemental analysis of the Pb concentration of digested PbS Qdot suspensions, in combination with a measurement of the atomic Pb/S ratio.…”

Nonmonotonic Size Dependence in the Hole Mobility of Methoxide-Stabilized PbSe Quantum Dot Solids

“…10,11 To fabricate cross-linked QDS, we apply a 5.0 mM solution of tetrabutylammonium hydroxide (TBA-OH) in methanol to spin-cast thin films. The solution is described by the equilibrium…”

In situ measurement of exciton energy in hybrid singlet-fission solar cells

“…Hence, the ability to synthesize nanocrystals of different sizes leads to mate rials with different state energies. Additionally, when the nanocrys tal size series is composed of the same inorganic semiconductor and organic ligands, the state tunability (including the energy of the lowest energy absorption) is largely decoupled from the bulk dielectric and chemical properties of the materials 39,40 . Thus, by incorporating nanocrystals with different sizes and hence different state energies into working devices, it is possible to assess energetic parameters of device performance.…”