Strong Electronic Coupling and Ultrafast Electron Transfer between PbS Quantum Dots and TiO₂ Nanocrystalline Films

Abstract

Hot carrier and multiple exciton extractions from lead salt quantum dots (QDs) to TiO(2) single crystals have been reported. Implementing these ideas on practical solar cells likely requires the use of nanocrystalline TiO(2) thin films to enhance the light harvesting efficiency. Here, we report 6.4 ± 0.4 fs electron transfer time from PbS QDs to TiO(2) nanocrystalline thin films, suggesting the possibility of extracting hot carriers and multiple excitons in solar cells based on these materials.

Enhanced photoelectrochemical and photocatalytic activities of CdS nanowires by surface modification with MoS2 nanosheets

“…The spectrum for pure CdS shows a broad emission band at 525 nm with some weaker bands to red due to bandgap trap states. With increasing loading of MoS 2 from 1% to 5%, both the band-edge and trap state emissions of CdS decreased, indicating more non-radiative recombination [37], attributed to electron transfer from the conduction band of CdS to MoS 2 . With further increasing amount of MoS 2 to about 10%, the emissions from CdS almost disappeared, due to complete quenching by MoS 2 .…”

Synergistic Doping of Fullerene Electron Transport Layer and Colloidal Quantum Dot Solids Enhances Solar Cell Performance

“…A bandgap of 1.1 eV was used for CQDs to account for the difference between the optical and electronic bandgaps and density of states tails. Neutral defects were introduced at 0.25 eV below the conduction band of CQDs as a single effective level with a 10 16 cm −3 density and capture crosssections adjusted to achieve the experimentally observed diffusion length of 80 nm [ 7 ] and lifetime of 120 ns [ 30 ] for a chosen mobility of 2 × 10 −2 cm 2 V −1 s −1 . [ 31 ] Neutral interface traps were introduced at the TiO 2 -CQD interface with a 10 12 cm −2 surface density.…”

Multiple exciton generation in quantum dot-based solar cells

“…In lead chalcogenide QDs, the latter process proceeds on 20−200 ps time scales [51,124]. As mentioned previously, charge separation can be at least two orders of magnitude faster if an ionising interface is in close proximity to the generated exciton [110]. Considering the high absorption cross-section of QDs in the spectral region relevant for MEG (i.e.…”

“…Auger recombination), which is governed by the same matrix element, no difference in recombination timescales as a function of apparent quantum confinement has been found in the series PbS, PbSe and PbTe [31,69]. Considering ultra-fast exciton separation close to QD-MO interfaces (see Section 3.1) [110] and material independent Auger kinetics, it is conceivable that the higher MEG yields for heavy lead chalcogenide QD devices is due [26,27,46,117].…”

“…Such a close proximity to the interface has been shown to favour ultra-fast charge injection (<50 fs) which inhibits MEG loss processes like Auger recombination (see Figure 2) by separating charge carriers before they can recombine [110]. Importantly, tailoring the energetics between MO acceptor and QD donor through surface ligands has been shown to affect this electron transfer rate significantly [111,112].…”