This theoretical work shows that ultra-thin InGaAs solar cells can have the operation of a hot carrier solar cell. Considering a quantum modeling of the electronic transport we show that the open circuit voltage Voc increases with an energy-selective contact considered between the absorber and the reservoir. Moreover, we do not observe the feared corresponding current degradation. The Voc improvement agrees with a simple and general expression based on the isentropic carrier extraction, confirming the link between the voltage and the carrier temperature. Concerning the current, as already shown in a precedent work, if carriers are confined in the absorber the current across an energy-selective contact is of the same order of magnitude as that obtained without selectivity. This advantageous behavior is explained by the hybridation of states in the absorber and in the reservoir.
Transport and charge separation are crucial steps in molecular or hybrid energy converters. We have developed a theoretical-numerical framework within the nonequilibrium Green’s function formalism to investigate the time-dependent transport of charges and energy, including the Coulomb interaction in the Hartree-Fock approximation. We thus analyze charge transport and separation in a donor-acceptor nanojunction illuminated with a femtosecond laser pulse. Our analysis conducts us to depart from the standard view of static density of states and driving energy, and to rather define and handle dynamical quantities on which relying to design ultrafast optoelectronics and highly efficient photovoltaics.
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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