Face-Dependent Electron Transfer in CdSe Nanoplatelet–Methyl Viologen Complexes

Abstract

Charge separation in colloidal semiconductor nanocrystals (CSNCs) is one of the key processes for the development of highly efficient solar cells. Several types of CSNCs have been recently synthesized with controlled quantum confinement dimensionality such as quantum dots (QDs), nanorods (NRs), and nanoplatelets (NPLs). However, previous studies on the carrier extraction dynamics from CSNCs have focused on QDs and NRs. Here, we analyzed the electron transfer process from colloidal CdSe NPLs to methyl viologen (MV 2+ , electron acceptor) using luminescence decay measurements and femtosecond pump−probe spectroscopy. We examined the dependence of the electron transfer dynamics on the lateral size of CdSe NPLs and found that the rate of electron transfer from CdSe NPLs to MV 2+ depends on the NPL face where MV 2+ adsorbs. In addition, we analyzed the growth kinetics and initial bleach amplitude at the band-edge bleach of CdSe NPLs and CdSe NPL−MV 2+ complexes and found that, in contrast with the behavior of CdSe QD−MV 2+ and NR−MV 2+ complexes, hot electron transfer does not occur. This result is a consequence of fast intraband relaxation in CdSe NPLs and the relatively slow electron transfer process.

Hot electron transfer in Zn–Ag–In–Te nanocrystal–methyl viologen complexes enhanced with higher-energy photon excitation

“…†) according to a previous report on CdSe-MV 2+ complexes. 11,21 The average number of MV 2+ molecules adsorbed on a ZAITe NC was estimated to 16. A further increase in the number of adsorbed MV 2+ molecules in a complex resulted in the aggregation of ZAITe NC-MV 2+ complexes due to the decrease in solubility of ZAITe NCs in octane.…”

“…Charge separation dynamics with the use of various electron acceptors has been reported in many papers. [5][6][7][8][9][10][11][12][13][14][15][16][17] For example Banin et al reported that hybrid nanostructures of Au-tipped CdS nanorods with a larger Au size exhibited a higher probability for charge separation of multiple excitons formed in the CdS nanocrystals, improving the photocatalytic activity for H 2 generation. 15 The rate of photoinduced electron transfer from CdSe NCs to methyl viologen (MV 2+ ) was shown to be dependent on the particle morphology: plate-like CdSe NCs exhibited a slower rate than that of spherical or rod-shaped CdSe NCs due to the weak electronic coupling along the short and long axes in the lateral dimension.…”

“…15 The rate of photoinduced electron transfer from CdSe NCs to methyl viologen (MV 2+ ) was shown to be dependent on the particle morphology: plate-like CdSe NCs exhibited a slower rate than that of spherical or rod-shaped CdSe NCs due to the weak electronic coupling along the short and long axes in the lateral dimension. 11 Furthermore, various systems for efficiently utilizing hot carriers photogenerated in NCs have been proposed. 18,19 Alivisatos et al reported that PbSe NC arrays exhibited a transient photocurrent with a high excitation intensity, the current obtained being 6-9 orders of magnitude higher than a dark current due to the fast tunneling process of hot carriers produced via Auger recombination of multiple excitons.…”

Molecular Polaritons Generated from Strong Coupling between CdSe Nanoplatelets and a Dielectric Optical Cavity

“…The system demonstrated here has the potential for investigating polariton mediated charge transfer [31][32][33][34] where the cavity can significantly influence the photo-induce charge transfer reaction from NPLs to acceptor molecules such as methyl viologen. 35 In a separate direction, our current investigation will pave the way toward to explore the transduction of quantum states among various physical degrees of freedom (electronic, vibronic, polaritonic), providing the emerging quantum information science field the knowledge for preparing next generation quantum systems.…”

An Ultrafast Transient Absorption Study of Charge Separation and Recombination Dynamics in CdSe QDs and Methyl Viologen: Dependence on Surface Stoichiometry

“…A similar electron transfer rate (1‐2 X 10 13 s −1 ) is observed between zero‐ and one‐dimensional semiconductor nanoparticles and MV +2 , but for two‐dimensional semiconductor nanoparticles, the rate is found to be slower by an order of magnitude, and the observation is attributed to weak electronic coupling along the short and long axes . The size‐dependence of nanoparticles on the rate of electron transfer has also been studied and the findings show a higher rate for the smaller size particles . Though the effect of size and shape of the nanoparticles on charge separation and recombination dynamics is well studied, the influence of their stoichiometry on these processes is largely unexplored.…”