Assessment of carrier-multiplication efficiency in bulk PbSe and PbS
Assessment of carrier-multiplication efficiency in bulk PbSe and PbS
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DOI：
10.1038/nphys1393
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发表时间：
2009-11-01
期刊：
影响因子：
19.6
通讯作者：
Bonn, M.
中科院分区：
文献类型：
--
作者：
Pijpers, J. J. H.;Ulbricht, R.;Bonn, M.
限制太阳能电池效率的重要因素之一是入射光子产生一个电子空穴对，而与光子能量无关。任何多余的光子能量都以热的形式损失。因此，每个光子可能产生多个电荷载流子（载流子倍增）对于未来的太阳能电池（1）具有很大的意义。已知载流子倍增发生在体半导体中，但由于其离散能级和增强的库仑相互作用，认为在纳米晶体材料如量子点中载流子倍增显著增强（1-3）。与此预期相反，我们在这里证明，对于一个给定的光子能量，载流子倍增发生在散装PbS和PbSe比在相同材料的量子点更有效。使用紧束缚计算定量地再现了体材料中测量的载流子倍增效率，这表明量子点中降低的载流子倍增效率可以归因于这些结构中降低的态密度。
One of the important factors limiting solar-cell efficiency is that incident photons generate one electron-hole pair, irrespective of the photon energy. Any excess photon energy is lost as heat. The possible generation of multiple charge carriers per photon (carrier multiplication) is therefore of great interest for future solar cells(1). Carrier multiplication is known to occur in bulk semiconductors, but has been thought to be enhanced significantly in nanocrystalline materials such as quantum dots, owing to their discrete energy levels and enhanced Coulomb interactions(1-3). Contrary to this expectation, we demonstrate here that, for a given photon energy, carrier multiplication occurs more efficiently in bulk PbS and PbSe than in quantum dots of the same materials. Measured carrier-multiplication efficiencies in bulk materials are reproduced quantitatively using tight-binding calculations, which indicate that the reduced carrier-multiplication efficiency in quantum dots can be ascribed to the reduced density of states in these structures.