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

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 (MV2+, 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 MV2+ depends on the NPL face where MV2+ adsorbs. In addition, we analyzed the growth kinetics and initial bleach amplitude at the band-edge bleach of CdSe NPLs and CdSe NPL-MV2+ complexes and found that, in contrast with the behavior of CdSe QD-MV2+ and NR-MV2+ 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.