  A standardized method for measuring thermophotovoltaic (TPV) efficiency has
not been yet established, which makes the reported results difficult to
compare. Besides, most of the TPV efficiencies reported to date have been
obtained using small view factors, i.e., large cell-to-emitter distances, so
the impact of the series resistance is usually underestimated, and the optical
cavity effects, i.e., the multiple reflections taking place between the emitter
and the cell, are not accounted for experimentally. In this work, we present an
experimental setup able to measure the TPV efficiency under high view factors
(up to 0.98), by using small emitter-to-cell distances (< 1 mm). This allows a
more accurate direct measurement of the TPV efficiency at higher power
densities than previous works. As a result, a TPV efficiency of 26.4+-0.1 % and
a power density of 4.3+-0.8 W/cm2 have been obtained for an InGaAs TPV cell
with a back surface reflector irradiated by a graphite thermal emitter at 1592
C.
