Electronic and surface properties of PbS nanoparticles exhibiting efficient multiple exciton generation

Abstract

Ultrafast transient absorption measurements have been used to study multiple exciton generation in solutions of PbS nanoparticles vigorously stirred to avoid the effects of photocharging. The threshold and slope efficiency of multiple exciton generation are found to be 2.5 ± 0.2 ×E(g) and 0.34 ± 0.08, respectively. Photoemission measurements as a function of nanoparticle size and ageing show that the position of the valence band maximum is pinned by surface effects, and that a thick layer of surface oxide is rapidly formed at the nanoparticle surfaces on exposure to air.

In Situ Synthesis of PbS Nanocrystals in Polymer Thin Films from Lead(II) Xanthate and Dithiocarbamate Complexes: Evidence for Size and Morphology Control

“…2,18,19 In addition, reports of multiple exciton generation in PbS quantum dots have demonstrated the potential for PbS based devices to exceed the ShockleyQueisser limit. [20][21][22] Typically hybrid photovoltaic devices have been fabricated by first synthesising semiconductor nanocrystals ex situ in the solution phase; long chain ligands are typically employed to control growth and disperse the nanocrystals in organic solvents suitable for film production. 18,23,24 The requirement for ligands, that contain long alkyl chains, is potentially detrimental to device performance.…”

Chemically-specific time-resolved surface photovoltage spectroscopy: Carrier dynamics at the interface of quantum dots attached to a metal oxide

“…The preparation and characterisation of the QDs have been detailed elsewhere [19]. The type I (core-only) PbS QD sample used has been shown to exhibit MEG for photon energies greater than~2.5 times the effective band gap [1]. The PbS QD sample was monitored using XPS of the Pb 4f core level, whilst the CdS/ZnSe QD was monitored simultaneously with the ZnO substrate due to the presence of zinc in both substrate and QD; a Zn 3d species associated with the QD (chemically shifted to a higher BE) was fitted along with the dominant Zn 3d peak associated with the substrate.…”

“…This is particularly the case for solar harvesting technologies, where a clear understanding of the dynamics of photoexcited carriers is of key fundamental importance. One such example is in devices utilising cost-reducing photovoltaic materials such as light-harvesting colloidal quantum dots (QDs) [1,2] where a transparent conducting oxide (TCO) such as ZnO is used as photoanode [3][4][5]. These QDs have been shown to exhibit multiple exciton generation (MEG, creation of more than one pair of charge carriers from a single photon) for photon energies greater than around twice the effective band gap.…”

“…These QDs have been shown to exhibit multiple exciton generation (MEG, creation of more than one pair of charge carriers from a single photon) for photon energies greater than around twice the effective band gap. The band gap is typically 1.0 eV, meaning MEG is present at wavelengths within the solar spectrum, giving potential for photovoltaic devices with enhanced efficiencies [1]. Considerable effort is currently being devoted to extending the photoexcited electron-hole pair lifetime in order to maximise the benefit of MEG.…”

Growth of nanocrystalline thin films of metal sulfides [CdS, ZnS, CuS and PbS] at the water–oil interface

“…The binding energies of the spectra were calibrated to literature values for the S(2p) peak from PbS. 17 Shirley-type backgrounds were subtracted and Gaussian/Lorentzian sum functions used to t the line shapes. The spin-orbit splitting of the doublets was set as 1.2 eV for the S(2p) peaks, and the doublet intensity ratio was set as 2 : 1.…”