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Enhanced Multiple Exciton Generation in PbS|CdS Janus-like Heterostructured Nanocrystals
Kroupa, Daniel M.,Pach, Gregory F.,Vö,rö,s, Má,rton,Giberti, Federico,Chernomordik, Boris D.,Crisp, Ryan W.,Nozik, Arthur J.,Johnson, Justin C.,Singh, Rohan,Klimov, Victor I.,Galli, American Chemical Society 2018 ACS NANO Vol.12 No.10
<P>Generating multiple excitons by a single high-energy photon is a promising third-generation solar energy conversion strategy. We demonstrate that multiple exciton generation (MEG) in PbS|CdS Janus-like heteronanostructures is enhanced over that of single-component and core/shell nanocrystal architectures, with an onset close to two times the PbS band gap. We attribute the enhanced MEG to the asymmetric nature of the heteronanostructure that results in an increase in the effective Coulomb interaction that drives MEG and a reduction of the competing hot exciton cooling rate. Slowed cooling occurs through effective trapping of hot-holes by a manifold of valence band interfacial states having both PbS and CdS character, as evidenced by photoluminescence studies and <I>ab initio</I> calculations. Using transient photocurrent spectroscopy, we find that the MEG characteristics of the individual nanostructures are maintained in conductive arrays and demonstrate that these quasi-spherical PbS|CdS nanocrystals can be incorporated as the main absorber layer in functional solid-state solar cell architectures. Finally, based upon our analysis, we provide design rules for the next generation of engineered nanocrystals to further improve the MEG characteristics.</P> [FIG OMISSION]</BR>
Kim, Sungwoo,Marshall, Ashley R.,Kroupa, Daniel M.,Miller, Elisa M.,Luther, Joseph M.,Jeong, Sohee,Beard, Matthew C. American Chemical Society 2015 ACS NANO Vol.9 No.8
<P>We developed a single step, cation-exchange reaction that produces air-stable PbSe quantum dots (QDs) from ZnSe QDs and PbX<SUB>2</SUB> (X = Cl, Br, or I) precursors. The resulting PbSe QDs are terminated with halide anions and contain residual Zn cations. We characterized the PbSe QDs using UV–vis–NIR absorption, photoluminescence quantum yield spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Solar cells fabricated from these PbSe QDs obtained an overall best power conversion efficiency of 6.47% at one sun illumination. The solar cell performance without encapsulation remains unchanged for over 50 days in ambient conditions; and after 50 days, the National Renewable Energy Laboratory certification team certified the device at 5.9%.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-8/acsnano.5b02326/production/images/medium/nn-2015-02326t_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b02326'>ACS Electronic Supporting Info</A></P>