Optoelectronic Materials section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628BL Delft, The Netherlands.
Nat Commun. 2013;4:2360. doi: 10.1038/ncomms3360.
Carrier multiplication, the generation of multiple electron-hole pairs by a single photon, is of great interest for solar cells as it may enhance their photocurrent. This process has been shown to occur efficiently in colloidal quantum dots, however, harvesting of the generated multiple charges has proved difficult. Here we show that by tuning the charge-carrier mobility in quantum-dot films, carrier multiplication can be optimized and may show an efficiency as high as in colloidal dispersion. Our results are explained quantitatively by the competition between dissociation of multiple electron-hole pairs and Auger recombination. Above a mobility of ~1 cm(2) V(-1) s(-1), all charges escape Auger recombination and are quantitatively converted to free charges, offering the prospect of cheap quantum-dot solar cells with efficiencies in excess of the Shockley-Queisser limit. In addition, we show that the threshold energy for carrier multiplication is reduced to twice the band gap of the quantum dots.
载流子倍增，即单个光子产生多个电子-空穴对的过程，对太阳能电池非常有吸引力，因为它可以提高光电流。这一过程已被证明在胶体量子点中高效发生，然而，所产生的多电荷的收集却被证明很困难。在这里，我们表明通过调整量子点薄膜中的载流子迁移率，可以优化载流子倍增，其效率可能与胶体分散相一样高。我们的结果通过多电子-空穴对的离解和俄歇复合之间的竞争得到定量解释。在迁移率大于约 1 cm(2) V(-1) s(-1)时，所有电荷都逃脱了俄歇复合，并被定量转化为自由电荷，为效率超过肖克利-奎塞尔极限的廉价量子点太阳能电池提供了前景。此外，我们表明载流子倍增的阈值能量降低到量子点带隙的两倍。
