Fundamental advantages of multijunction thermophotovoltaic cells

In this paper, we examine some basic advantages of multijunction cells used for thermophotovoltaics (TPV), in terms of greater fraction of spectrum used, reduced carrier thermalization losses, and reduced series resistance. We find that increasing the fraction of the thermal spectrum used with tandem TPV cells is important in real-world TPV systems where there are non-ideal optical losses. The lower currents and higher voltages of 2-junction and 4-junction TPV cells modeled here compared to single-junction cells result in substantially lower series resistance losses. Considering one potentially significant disadvantage of series-connected multijunction cells – the need for subcell current matching – we also examine the effect of 2-junction and 4-junction TPV cells on the practical depth of discharge of thermal batteries, and the energy that can be extracted from each thermal charge.