Enhanced Charge Transport and Excited-State Charge-Transfer Dynamics in a Colloidal Mixture of CdTe and Graphene Quantum Dots

Abstract

Semiconductor quantum dot (QD)–graphene composites are promising materials for photovoltaics and photocatalysis because of efficient charge extraction and transport property of graphene. Analysis of their ultrafast carrier-transfer dynamics has been limited to only QD–graphene sheets, such as CdTe–graphene sheets and CdS–graphene sheets. Herein, we investigate the carrier-transfer dynamics of CdTe QDs (CdTe QDs) in the presence and absence of graphene QDs (GQDs) by using femtosecond transient absorption spectroscopy. Although the surfaces of both the QDs are in negatively charged state, as evident from the zeta potential measurements, we observed a strong excited-state interaction between two similarly charged QDs, leading to an efficient quenching of the excitonic emission of the CdTe QDs in the presence of GQDs. A detailed analysis of the rise time and 1S bleach recovery provides the evidence of electron transfer from CdTe QDs to GQDs with the hole-trapping process by surface defects. On the basis of the mechanistic study, an overall charge-transfer scheme that accounts for the faster bleach recovery of CdTe QDs in the presence of GQDs is proposed. Moreover, we have evidenced the consequences of charge transfer through the measurements of improved four-probe photoconductivity (from 1.39 (±0.12) × 10–4 S m–1 to 1.47 (±0.24) × 10–3 S m–1) and decreased charge-transfer resistance [from 6944 (±0.3) to 5761 (±0.3) Ω] exhibited by CdTe QDs in the presence of GQDs. These findings described in the present study are hoped to open up design strategies for developing light-harvesting inorganic–organic hybrid QD assemblies with better efficiency.

Preparation and Characterization of Freely-Suspended Graphene Nanomechanical Membrane Devices with Quantum Dots for Point-of-Care Applications

“…In Figure 5b, emission intensity characteristic was compared between the pristine donor CdTe and the donor CdTe loaded-NMMs to understand the interaction between donor CdTe and NMM under donor CdTe excitation light (480 nm). Emission characteristic in Figure 5b shows that CdTe emission was quenched when it was grafted onto NMM due to the energy transfer from fluorophores of CdTe to the graphene based NMM [19,[47][48][49][50][51][52]. However, when we compared the emission quenching intensities, emission quenching rate of CdTe attached on GML sample emission quenching rate was higher than the CdTe attached on GOL sample.…”

“…Bandgap of the small-size donor dot (2.2 nm CdTe) was larger than the big-size acceptor dot (3.1 nm CdTe), due to the reciprocal proportion of the bandgap energy with the nanocrystal size [52][53][54].…”

“…Figure 5c shows the absorption and emission spectra with the spectral overlap region between emission of donor CdTe and absorption of acceptor CdTe where the FRET occurs when the dipole-dipole coupling is provided and molecular distance is less than 10 nm between donor and acceptor molecules under donor excitation light [13,19,[49][50][51][52][53][54].…”

“…In Figure 6a,b, proposed mechanisms and schematic illustrations with energy levels, energy and charge transfers are shown for defining the relationship between the materials [19,29,[49][50][51][52][53][54].…”

Фотодинамика люминесценции гибридных наноструктур InP/InAsP/InP ННК, пассивированных слоем ТОРО-CdSe/ZnS КТ

“…Гибридные полупроводниковые наноструктуры активно исследуются в последнее время. Особый интерес представляет создание композитов из полупроводниковых материалов различной размерности [1][2][3][4][5][6], подразумевающие их широкое практическое применение. Очевидно, что применение нанокомпозитов требует понимания характера межфазной фотодинамики и особенностей взаимодействий, которые связывают экситонные и поверхностные состояния.…”