Feedback-driven optimization of hot-carrier solar cell

Abstract

Solar cells convert energy absorbed from the sun into electrical power and they are therefore of high interest for green energy solutions. Ongoing research to improve solar cells deals with a broad range of aspects from improved light absorption to pushing the limits of efficiency searching for keys in materials research and device design. Hot-carrier solar cells, which are at the focus of this thesis aim at improving the output power of a solar cell by exploiting the excess energy of the light-generated charge carriers, which is lost in fast relaxation processes in standard solar cells. The drawback of these hot-carrier solar cells is however that low-energy charge carriers are not exploited for power generation. In this thesis, we propose and theoretically analyse a feedback mechanism to adapt the energy-filtering scheme for the extraction of hot carriers to the nonequilibrium conditions under which the solar cell is operated. This is done by coupling a quantum dot to the electron collector, which thereby measures the collector’s potential. This quantum dot is furthermore capacitively coupled to the energy filter, so that it modifies its properties depending on the collector potential. We demonstrate that this feedback can improve the charging time, when the solar cell is used to charge a battery, and it can improve the power generated, when the solar cell is connected to a circuit with a load. In this thesis we use a scattering matrix approach to model the solar cell operation. The load resistance or battery capacitance, as well as the filter properties enter the model through general variables, which could in the future be adapted to experimentally relevant conditions, in order to test the opportunities of this proposal for realistic devices.