Nozik A J
Center for Basic Sciences, National Renewable Energy Laboratory, Golden, Colorado 80401, USA. arthur@
Inorg Chem. 2005 Oct 3;44(20):6893-9. doi: 10.1021/ic0508425.
Huge amounts of carbon-free energy will be required during the coming decades in order to stabilize atmospheric CO2 to acceptable levels. Solar energy is the largest source of non-carbonaceous energy and can be used to produce both electricity and fuel. However, the ratio of the areal cost to the conversion efficiency for devices converting solar photons to electricity or fuel must be reduced by at least 1 order of magnitude from the present values; this requires large increases in the cell efficiency and large reductions in the cost per unit area. We have shown how semiconductor quantum dots may greatly increase photon conversion efficiencies by producing multiple excitons from a single photon. This is possible because quantization of energy levels in quantum dots slows the cooling of hot excitons, promotes multiple exciton generation, and lowers the photon energy threshold for this process. Quantum yields of 300% for exciton formation in PbSe quantum dots have been reported at photon energies 3.8 times the HOMO-LUMO transition energy, indicating the formation of three excitons/photon for all photoexcited quantum dots. Similar high quantum yields have also been reported for PbS quantum dots. A new model for this effect that is based on a coherent superposition of multiple excitonic states has been proposed.
在未来几十年里，为了将大气中的二氧化碳稳定在可接受的水平，将需要大量的无碳能源。太阳能是最大的非碳能源来源，可用于生产电力和燃料。然而，将太阳能光子转换为电力或燃料的设备的面积成本与转换效率之比必须从目前的值至少降低1个数量级；这需要大幅提高电池效率并大幅降低单位面积成本。我们已经展示了半导体量子点如何通过从单个光子产生多个激子来极大地提高光子转换效率。这是可能的，因为量子点中的能级量子化减缓了热激子的冷却，促进了多激子的产生，并降低了该过程的光子能量阈值。在光子能量为HOMO-LUMO跃迁能量的3.8倍时，已报道PbSe量子点中激子形成的量子产率为300%，这表明所有光激发的量子点都形成了三个激子/光子。对于PbS量子点也报道了类似的高量子产率。已经提出了一种基于多个激子态的相干叠加的这种效应的新模型。
