Power conversion in a thermophotovoltaic (TPV) system can be accomplished with single p‐n junctions which are interconnected on‐wafer (monolithic interconnected module (MIM) approach) or off‐wafer (individual chip module approach) to form large area arrays. Using a MIM architecture, 0.6 eV InGaAs diodes grown lattice mismatched to InP have produced a power conversion efficiency of 23% and a power density of 0.65 W/cm2 at cell and radiator temperatures of 25°C and 1000°C, respectively. A shortcoming of a single p‐n junction is inefficient use of the incident spectrum due to over‐excitation losses from high, above bandgap energy photons. In order to overcome these losses, tandem TPV devices have been proposed which comprise two or more p‐n junctions of differing bandgaps. In this work we report on the growth, fabrication and characterization of InGaAsP/InGaAs (0.72/0.60 eV) tandem TPV diodes. Electrical measurements using a grey body source reveal an open circuit voltage of 0.504 V/cell and a fill factor of 72.3% at a short circuit current density of 0.069 A/cm2 and a cell temperature of 25°C.

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