Carrier multiplication in semiconductor nanocrystals: Influence of size, shape, and composition

Lazaro A. Padilha, John T. Stewart, Richard L. Sandberg, Wan Ki Bae, Weon Kyu Koh, Jeffrey M. Pietryga, Victor I Klimov

Research output: Contribution to journalArticle

109 Citations (Scopus)

Abstract

During carrier multiplication (CM), also known as multiexciton generation (MEG), absorption of a single photon produces multiple electron-hole pairs, or excitons. This process can appreciably increase the efficiency of photoconversion, which is especially beneficial in photocatalysis and photovoltaics.This Account reviews recent progress in understanding the CM process in semiconductor nanocrystals (NCs), motivated by the challenge researchers face to quickly identify candidate nanomaterials with enhanced CM. We present a possible solution to this problem by showing that, using measured biexciton Auger lifetimes and intraband relaxation rates as surrogates for, respectively, CM time constants and non-CM energy-loss rates, we can predict relative changes in CM yields as a function of composition. Indeed, by studying PbS, PbSe, and PbTe NCs of a variety of sizes we determine that the significant difference in CM yields for these compounds comes from the dissimilarities in their non-CM relaxation channels, i.e., the processes that compete with CM. This finding is likely general, as previous observations of a material-independent, "universal" volume-scaling of Auger lifetimes suggest that the timescale of the CM process itself is only weakly affected by NC composition.We further explore the role of nanostructure shape in the CM process. We observe that a moderate elongation (aspect ratio of 6-7) of PbSe NCs can cause up to an approximately two-fold increase in the multiexciton yield compared to spherical nanoparticles. The increased Auger lifetimes and improved charge transport properties generally associated with elongated nanostructures suggest that lead chalcogenide nanorods are a promising system for testing CM concepts in practical photovoltaics.Historically, experimental considerations have been an important factor influencing CM studies. To this end, we discuss the role of NC photocharging in CM measurements. Photocharging can distort multiexciton dynamics, leading to erroneous estimations of the CM yield. Here, we show that in addition to distorting time-resolved CM signals, photocharging also creates spectral signatures that mimic CM. This re-emphasizes the importance of a careful analysis of the potential effect of charged species in both optical and photocurrent-based measurements of this process.

Original languageEnglish
Pages (from-to)1261-1269
Number of pages9
JournalAccounts of Chemical Research
Volume46
Issue number6
DOIs
Publication statusPublished - Jun 18 2013

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Nanocrystals
Semiconductor materials
Chemical analysis
Nanostructures
Photocatalysis
Nanorods
Photocurrents
Nanostructured materials
Transport properties
Charge transfer
Aspect ratio
Elongation
Energy dissipation
Photons
Nanoparticles
Electrons
Testing
lead selenide

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Padilha, L. A., Stewart, J. T., Sandberg, R. L., Bae, W. K., Koh, W. K., Pietryga, J. M., & Klimov, V. I. (2013). Carrier multiplication in semiconductor nanocrystals: Influence of size, shape, and composition. Accounts of Chemical Research, 46(6), 1261-1269. https://doi.org/10.1021/ar300228x

Carrier multiplication in semiconductor nanocrystals : Influence of size, shape, and composition. / Padilha, Lazaro A.; Stewart, John T.; Sandberg, Richard L.; Bae, Wan Ki; Koh, Weon Kyu; Pietryga, Jeffrey M.; Klimov, Victor I.

In: Accounts of Chemical Research, Vol. 46, No. 6, 18.06.2013, p. 1261-1269.

Research output: Contribution to journalArticle

Padilha, LA, Stewart, JT, Sandberg, RL, Bae, WK, Koh, WK, Pietryga, JM & Klimov, VI 2013, 'Carrier multiplication in semiconductor nanocrystals: Influence of size, shape, and composition', Accounts of Chemical Research, vol. 46, no. 6, pp. 1261-1269. https://doi.org/10.1021/ar300228x
Padilha LA, Stewart JT, Sandberg RL, Bae WK, Koh WK, Pietryga JM et al. Carrier multiplication in semiconductor nanocrystals: Influence of size, shape, and composition. Accounts of Chemical Research. 2013 Jun 18;46(6):1261-1269. https://doi.org/10.1021/ar300228x
Padilha, Lazaro A. ; Stewart, John T. ; Sandberg, Richard L. ; Bae, Wan Ki ; Koh, Weon Kyu ; Pietryga, Jeffrey M. ; Klimov, Victor I. / Carrier multiplication in semiconductor nanocrystals : Influence of size, shape, and composition. In: Accounts of Chemical Research. 2013 ; Vol. 46, No. 6. pp. 1261-1269.
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