Space-separated quantum cutting with silicon nanocrystals for photovoltaic applications

For optimal energy conversion in photovoltaic devices (electricity to and from light) one important requirement is that the full energy of the photons is used. However, in solar cells, a single electron-hole pair of specific energy is generated when the incoming photon energy is above a certain threshold, with the excess energy being lost to heat. In the so-called quantum-cutting process, a high-energy photon can be divided into two, or more, photons of lower energy. Such manipulation of photon quantum size can then very effectively increase the overall efficiency of a device. In the current work, we demonstrate (space-separated) photon cutting by silicon nanocrystals, in which nearby Er3 ions and neighbouring nanocrystals are used to detect this effect. © 2008 Nature Publishing Group

Step-like enhancement of luminescence quantum yield of silicon nanocrystals

Carrier multiplication by generation of two or more electron-hole pairs following the absorption of a single photon may lead to improved photovoltaic efficiencies1 and has been observed in nanocrystals made from a variety of semiconductors, including silicon. However, with few exceptions 2, these reports have been based on indirect ultrafast techniques3-6. Here, we present evidence of carrier multiplication in closely spaced silicon nanocrystals contained in a silicon dioxide matrix by measuring enhanced photoluminescence quantum yield. As the photon energy increases, the quantum yield is expected to remain constant, or to decrease as a result of new trapping and recombination channels being activated. Instead, we observe a step-like increase in quantum yield for larger photon energies that is characteristic of carrier multiplication7. Modelling suggests that carrier multiplication is occurring with high efficiency and close to the energy conservation limit. © 2011 Macmillan Publishers Limited. All rights reserved