Proceedings of September Meeting 2016 (NFM16)
Publication date: 14th June 2016
In a conventional photovoltaic device photons are absorbed in a bulk semiconductor. This leads to electron-hole pairs with initial excess energy equal to the difference between the photon energy and the semiconductor band gap. In a bulk semiconductor the hot charges predominantly lose their excess energy as heat, which limits the efficiency of a photovoltaic device. In semiconductor nanomaterials the excess energy can be utilized by exciting additional electrons across the band gap. This process of carrier multiplication leads to formation of two or more electron-hole pairs for the absorption of one photon.
We studied charge carrier photogeneration, charge relaxation, charge mobility and decay in semiconductor PbSe quantum dot arrays, PbS nanosheets and 2D percolative networks of PbSe quantum dots, using ultrafast time-resolved laser spectroscopy with optical and terahertz conductivity detection.1-5 Effects of the nanogeometry of the material on the efficiency of carrier multiplication and charge dynamics will be discussed.
References
(1)Suchand Sandeep, C. S. et al., High charge-carrier mobility enables exploitation of carrier multiplication in quantum-dot films. Nat. Commun. 2013, 4, 2360, DOI: 10.1038/ncomms3360.
(2)Aerts, M. et al., Highly efficient carrier multiplication in PbS nanosheets. Nat. Commun. 2014, 5, 3789, DOI: 10.1038/ncomms4789.
(3)Boneschanscher, M. P. et al., Long-range orientation and atomic attachment of nanocrystals in 2D honeycomb superlattices. Science 2014, 344, 1377-1380.
(4)Evers, W. H. et al., High charge mobility in 2D percolative networks of PbSe quantum dots connected by atomic bonds. Nat. Commun., 2015, 6, 8195,doi:10.1038/ncomms9195(5)ten Cate, S. et al., Generating Free Charges by Carrier Multiplication in Quantum Dots for Highly Efficient Photovoltaics. Acc. Chem. Res. 2015, 48, 174-181.
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