Increasing the efficiency of thermophotovoltaic (TPV) systems is of interest for the exploitation of heat deriving from combustion processes in order to generate a proportion of electricity. Therefore, RSE has started a theoretical simulation activity to assess technological solutions that can improve the performance of the TPV device (the solar cell), which is the heart of every thermophotovoltaic conversion system of thermal power into electrical power. In particular, this study made it possible to assess the performance of a germanium TPV device equipped with a front SiGe passivating layer and an innovative dual functionality optical filter, i.e., a filter which, combined with a rear mirror, could act as both a reflector of photons that cannot be used by the cell and at the same time, as an anti-reflective coating capable of increasing the absorption of photons that can be used by the cell. The mathematical modelling carried out in collaboration with Università di Pavia allowed us to verify and confirm that the ideal innovative SiGe/Ge TPV device, when exposed to a blackbody source at a temperature of 1500 K, allows for an increase in efficiency from 6% to 30% compared to a usual ideal Ge TPV device and an increase in electrical power by 40%. The simulation also highlighted that the black body radiation absorbable by the germanium cell increases by a factor of 6, thus increasing the emission temperature from 1,500 K to 2,000 K. Therefore, the Ge TPV device maximises its performance in the processes that operate at high temperature. Furthermore, a new black body source was created and characterised. In particular, the methodology is described that was adopted to determine the emission temperature (1,420 K), the intensity (810 mW/cm2), the uniformity in the measurement plane of the TPV device (±10%) and the temporal stability (± 1%). Therefore, the new black body source was used to perform current-voltage measurements on traditional Ge TPV devices. The good agreement between experimental and simulated data made it possible to validate the mathematical models applied to simulate the performance of the TPV devices. Finally, the results obtained from the simulations and measurements carried out provided directions regarding the optimisation of the manufacturing processes of innovative germanium TPV devices.