  A new approach is introduced to significantly improve the performance of
thermophotovoltaic (TPV) systems by using low-dimensional thermal emitters and
photovoltaic (PV) cells. By reducing the thickness of both the emitter and the
PV cell, strong spectral selectivity in both thermal emission and absorption
can be achieved by confining photons in trapped waveguide modes inside the
thin-films that act as thermal analogs to quantum wells. Simultaneously,
photo-excited carriers travel shorter distances across the thin-films reducing
bulk recombination losses resulting in a lower saturation current in the PV
cell. We predict a TPV efficiency enhancement with near-field coupling between
the thermal emitter and the PV cell of up to 38.7% using a germanium (Ge)
emitter at 1000 K and a gallium antimonide (GaSb) cell with optimized
thicknesses separated by 100 nm. Even in the far-field limit, the efficiency is
predicted to reach 31.5%, which is an order of magnitude higher than the
Shockley Queisser limit of 1.6% for a bulk GaSb cell and a blackbody emitter at
1000 K. The proposed design approach does not require nanoscale patterning of
the emitter and PV cell surfaces, but instead offers a simple low-cost solution
to improve the performance of a thermophotovoltaic system.
