4 - Hot-Carrier Solar Cells: Modeling Carrier Transport

Abstract

Classical photovoltaic devices do not fully take advantage of the available solar energy because (i) part of the solar spectrum is not absorbed and (ii) part of the absorbed energy is dissipated as heat before carrier collection. Solar cells based on hot carrier collection aim at reducing the thermalization process (high voltage) while obtaining a high absorption (high current) are among the photovoltaic devices that could overcome these limitations. Such a device can be seen as a combination of a thermoelectric device that converts heat gradients into electrical energy and a photovoltaic device that converts light flux into electrical energy. In this chapter, we first present a model that mimics the basic working principle of such advanced solar cells on the basis of a detailed balance model. As a significant improvement on earlier hot carrier cell models, here, electrons and holes thermodynamic properties are considered individually so that it is not required that both share the same temperature. The model includes each carrier thermalization process with phonons and with the contacts. This model is shown to yield analytical solutions. It could also be generalized to include nonradiative recombination and Auger processes. In the second part, we present some examples of properties that could be studied, such the impact of the carriers effective masses, of each carrier-phonon thermalization rate, and on each contact transmission. The results of this modeling should help to better understand the principle of hot carriers solar cells and to design such devices.