Multiexciton Dynamics in Infrared-Emitting Colloidal Nanostructures Probed by a Superconducting Nanowire Single-Photon Detector

Abstract

Carrier multiplication (CM) is the process in which absorption of a single photon produces multiple electron-hole pairs. Here, we evaluate the effect of particle shape on CM efficiency by conducting a comparative study of spherical nanocrystal quantum dots (NQDs) and elongated nanorods (NRs) of PbSe using a time-resolved technique that is based on photon counting in the infrared using a superconducting nanowire single-photon photodetector (SNSPD). Due to its high sensitivity and low noise levels, this technique allows for accurate determination of CM yields, even with the small excitation intensities required for quantitative measurements, and the fairly low emission quantum yields of elongated NR samples. Our measurements indicate an up to ∼60% increase in multiexciton yields in NRs versus NQDs, which is attributed primarily to a decrease in the electron-hole pair creation energy. These findings suggest that shape control is a promising approach for enhancing the CM process. Further, our work demonstrates the effectiveness of the SNSPD technique for the rapid screening of CM performance in infrared nanomaterials.

Multiple exciton generation in quantum dot-based solar cells

“…Such a phonon scattering bottleneck is thus consistent with the high MEG yields observed in dispersed PbTe QDs [31,50,59] and is also in agreement with the high EQEs (>120%) reported for devices based on the same QD material [28]. Figure 3A) [46,68].…”

Multiple Exciton Generation in Nanostructures for Advanced Photovoltaic Cells

“…Initial reports showed the rst evidence of MEG [57,58]. In particular, in a paper by Cunningham et al [58], values of hω th and ε eh close to the ideal values of 2E g and E g were reported.…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…The possibility of multi-exciton generation (MEG), also called carrier multiplication (CM), has been investigated for several years, most commonly in Pb-chalcogenide NCs [166][167][168][169][170][171][172], but also for other NC materials [173][174][175][176]. In the process of multi-exciton generation, a hot carrier with excess energy higher than the bandgap can relax to the ground state while generating an additional electron-hole pair (Fig.…”

“…Ensemble transient absorption experiments are most commonly used to study multi-exciton dynamics in NCs [161,173,199,[203][204][205]. Analysis of the fast photoluminescence decay components of NCs under strong excitation can also provide information about multi-exciton decay rates [170,212]. Both methods rely on a significant multi-exciton population in the NCs, and therefore require strong laser excitation.…”