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Lead Telluride Quantum Dot Solar Cells Displaying External Quantum Efficiencies Exceeding 120%.



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Böhm, Marcus L 
Jellicoe, Tom C 
Tabachnyk, Maxim 
Davis, Nathaniel JLK 
Wisnivesky-Rocca-Rivarola, Florencia 


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.



Lead telluride quantum dots, multiple exciton generation, pump−push photocurrent spectroscopy, solar cells

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Nano Lett

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American Chemical Society (ACS)
Engineering and Physical Sciences Research Council (EP/G060738/1)
Engineering and Physical Sciences Research Council (EP/M005143/1)
Engineering and Physical Sciences Research Council (EP/G037221/1)
European Research Council (259619)
European Commission (312483)
M.L.B. thanks the German National Academic Foundation (Studienstiftung) for funding. This work was supported by the EPSRC (grant numbers EP/M005143/1, EP/G060738/1, EP/G037221/1) and the ERC (grant number 259619 PHOTO-EM). M.T. thanks the Gates Cambridge Trust and the Winton Programme for Sustainability for financial support. N.J.L.K.D. thanks the Cambridge Commonwealth European and International Trust, Cambridge Australian Scholarships and Mr Charles K Allen for financial support. F.W.R.R. thanks financial support from CNPq (grant number 246050/2012-8). C.D. acknowledges financial support from the EU under grant number 312483 ESTEEM2. A.A.B. is a Royal Society Research Fellow.