Journal
NANO LETTERS
Volume 15, Issue 12, Pages 7987-7993Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.5b03161
Keywords
Lead telluride quantum dots; solar cells; multiple exciton generation; pump-push photocurrent spectroscopy
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Funding
- German National Academic Foundation (Studienstiftung)
- EPSRC [EP/M005143/1, EP/G060738/1, EP/G037221/1]
- ERC [259619 PHOTO-EM]
- Gates Cambridge Trust
- Winton Programme for Sustainability
- Cambridge Commonwealth European and International Trust
- Cambridge Australian Scholarships
- CNPq [246050/2012-8]
- EU [312483 ESTEEM2]
- Engineering and Physical Sciences Research Council [EP/M507301/1, EP/G060738/1, EP/M005143/1, 1362124] Funding Source: researchfish
- EPSRC [EP/M507301/1, EP/G060738/1, EP/M005143/1] Funding Source: UKRI
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Multiple exciton generation (MEG) in semiconducting quantum dots is a process that produces multiple charge-carrier pairs from a single excitation. MEG is a possible route to bypass the Shockley-Queisser limit in single-junction solar cells but it remains challenging to harvest charge-carrier pairs generated by MEG in working photovoltaic devices. Initial yields of additional carrier pairs may be reduced due to ultrafast intraband relaxation processes that compete with MEG at early times. Quantum dots of materials that display reduced carrier cooling rates (e.g., PbTe) are therefore promising candidates to increase the impact of MEG in photovoltaic devices. Here we demonstrate PbTe quantum dot-based solar cells, which produce extractable charge carrier pairs with an external quantum efficiency above 120%, and we estimate an internal quantum efficiency exceeding 150%. Resolving the charge carrier kinetics on the ultrafast time scale with pump-probe transient absorption and pump-push-photocurrent measurements, we identify a delayed cooling effect above the threshold energy for MEG.
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