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/SiNx double AR coating including a high refractive index SiNx layer was studied. The SiNx 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 SiNx 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.