Comparing Multiple Exciton Generation in Quantum Dots To Impact Ionization in Bulk Semiconductors: Implications for Enhancement of Solar Energy Conversion
Comparing Multiple Exciton Generation in Quantum Dots To Impact Ionization in Bulk Semiconductors: Implications for Enhancement of Solar Energy Conversion
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DOI：
10.1021/nl101490z
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发表时间：
2010-08-01
期刊：
影响因子：
10.8
通讯作者：
Nozik, Arthur J.
中科院分区：
文献类型：
--
作者：
Beard, Matthew C.;Midgett, Aaron G.;Nozik, Arthur J.
量子点（QD）中的多激子产生（MEG）和体半导体中的碰撞电离（II）是描述每个吸收的光子产生多于一个电子空穴对的过程。我们推导出表达式的适当的方式来比较MEG量子点与II在散装半导体，并认为有重要的差异，散装半导体和量子点之间的物理。我们的分析表明，在一个给定的量子点中产生每个电子空穴对所需的能量的基本单位是带隙能量。我们发现，在PbSe量子点的倍增过程的效率增加了至少2相比，散装PbSe，而冷却和倍增之间的竞争有利于倍增的一个因素3量子点。我们还表明，在QD太阳能电池表现出MEG的功率转换效率可以大大超过其散装同行的转换效率，特别是如果MEG的阈值能量可以减少到两倍的QD带隙能量，这需要进一步增加MEG的效率。最后，我们讨论了与MEG在太阳能转换中实现最大效益相关的研究挑战，因为我们表明阈值和效率在数学上是相关的。
Multiple excitor) generation (MEG) in quantum dots (QDs) and impact ionization (II) in bulk semiconductors are processes that describe producing more than one electron hole pair per absorbed photon. We derive expressions for the proper way to compare MEG in QDs with II in bulk semiconductors and argue that there are important differences in the photophysics between bulk semiconductors and QDs. Our analysis demonstrates that the fundamental unit of energy required to produce each electron hole pair in a given QD is the band gap energy. We find that the efficiency of the multiplication process increases by at least 2 in PbSe QDs compared to bulk PbSe, while the competition between cooling and multiplication favors multiplication by a factor of 3 in QDs. We also demonstrate that power conversion efficiencies in QD solar cells exhibiting MEG can greatly exceed conversion efficiencies of their bulk counterparts, especially if the MEG threshold energy can be reduced toward twice the QD band gap energy, which requires a further increase in the MEG efficiency. Finally, we discuss the research challenges associated with achieving the maximum benefit of MEG in solar energy conversion since we show the threshold and efficiency are mathematically related.