Characterizing thermophotovoltaic cells

Performance of photovoltaic cells is often expressed in terms of conversion efficiency. For flat-plate and concentrator cells operating under natural sunlight, procedures have been established and standardized for determining their efficiency. These procedures rate the efficiency in terms of a reference temperature, reference total irradiance, reference spectral irradiance and a defined area. However, for thermophotovoltaic (TPV) devices, such reference conditions have not been established, resulting in large differences in efficiencies measured among various technologies and research groups. We discuss a strategy for determining a limited set of reference conditions to help compare TPV performance among technologies and groups. First, we measure the quantum efficiency and the current versus voltage (I-V) curves as a function of light-level and temperature. From this information, we can then determine the I-V characteristics at any current density for an arbitrary light source. We also present an alternative procedure to characterize PV cells in terms of the power produced divided by absorbed power. The discussion covers temperature, contacting, reference conditions and other measurement issues.