Vertical multi‐junction cells for thermophotovoltaic conversion

Photovoltaic energy conversion can be very efficient in a thermophotovoltaic (TPV) system where the emitted radiation is near the bandgap energy of the TPV cell. Limit conversion efficiencies greater than 50% are theoretically possible with near bandgap radiation at high power densities with ideal cell designs. The unique features and characteristics of the vertical multi‐junction (VMJ) cell structure make it ideally suited for efficient TPV conversion. Vertical junction unit cells are most responsive to near bandgap energy photons. Vertical contacts eliminate the need for conventional top and bottom ohmic contacts that obstruct light or impede reflection of lower than bandgap energy photons. These features and the inherent high‐voltage and low‐series resistance characteristics of the VMJ cell assures efficient operation at high power densities. Additionally, VMJ cells can be fabricated from silicon or germanium for many TPV applications from 1500 to 2500 °K.