Optimum efficiency of single and multiple bandgap cells in thermophotovoltaic energy conversion

Abstract

A theory is developed to examine the efficiency of multiple bandgap cells in thermophotovoltaic (TPV) energy conversion. Based on this general theory, explicit equations for the TPV efficiency of one- and two-bandgap cells are derived. The maximum TPV efficiency and optimum bandgap(s) are shown to depend on three parameters: the blackbody emitter temperature, the cell temperature and the magnitude of the parasitic absorption of below bandgap energy photons. For selected values of these parameters, the maximum TPV efficiency and associated bandgap(s) are calculated for the one-bandgap and the two-bandgap case. The maximum TPV efficiency for two bandgaps is approximately 10% larger than that for one bandgap. For reasonable values of emitter temperature, cell temperature and parasitic absorption, TPV efficiencies in excess of 35% and 40% appear feasible for one- and two-bandgap cells respectively.