Hot-carrier solar cells could overcome the Shockley-Queisser limit by having electrons and holes at a higher temperature than the lattice. To generate these hot carriers under concentrated sunlight, the thermalization rate should be as low as possible. Our objective in this presentation is to quantify the influence of different thermalization mechanisms. We determine the carrier temperature in ultrathin GaAs absorbers using continuous-wave photoluminescence and identify distinct surface and volume thermalization contributions. We explain the origin of these contributions using theoretical models involving non-equilibrium LO phonon populations and thermionic emission. We implement these mechanisms in detailed balance calculations for further understanding.
This theoretical study sheds light on questions raised by inter-subband transition in quantum dot intermediate band solar cells. Based on a dedicated analytical model that correctly treats, from a quantum point-of-view, the trade-off between the absorption, the recombination and the electronic transport, we clearly show that it is essential to control the transit rate between the excited state of the quantum dot and the embedding semiconductor with a tunnel barrier. Such a barrier, matching the recombination and the tunnel rates, allows to strongly improve the current. On the other hand, by better controlling the retrapping, such a barrier can also improve the voltage. Finally this work, by giving a framework to design efficient inter-subband transitions, opens new opportunities for quantum dot intermediate-band solar cells.
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