A germanium back contact type cell for thermophotovoltaics

A Ge back contact type photovoltaic cell has been proposed to reduce resistance loss for high current densities in thermophotovoltaic systems. This structure requires low surface recombination velocities. A SiO₂/SiN_x double AR coating including a high refractive index SiN_x layer was studied. The SiN_x layer has a high enough passivation effect to obtain high efficiency. The quantum efficiency was around 0.8 in the 800-1600 nm wavelength range. The efficiency for emitted infrared lights was estimated at 18% for a blackbody surface and 25% for a selective emitter. A higher efficiency will be obtained by using a low resistance substrate after the recombination loss is decreased, due to the improved SiN_x passivation layer and the floating emitter. It is considered that the Ge cell efficiency will increase in excess of 30% for infrared light by using these structures.