  We propose a solar thermal energy conversion system consisting of a solar
absorber, a thermoradiative cell or negative illumination photodiode, and a
photovoltaic cell. Because it is a heat engine, this system can also be paired
with thermal storage to provide reliable electricity generation. Heat from the
solar absorber drives radiative recombination current in the thermoradiative
cell, and its emitted light is absorbed by the photovoltaic cell to provide an
additional photocurrent. Based on the principle of detailed balance, we
calculate a limiting solar conversion efficiency of 85% for fully concentrated
sunlight and 45% for one sun with an absorber and single-junction cells of
equal areas. Ideal and nonideal solar thermoradiative-photovoltaic systems
outperform solar thermophotovoltaic converters for low bandgaps and practical
absorber temperatures. Their performance enhancement results from a high
tolerance to nonradiative generation/recombination and an ability to minimize
radiative heat losses. We show that a realistic device with all major losses
could achieve increases in solar conversion efficiency by up to 7.9% (absolute)
compared to a solar thermophotovoltaic device under low optical concentration.
Our results indicate that these converters could serve as efficient heat
engines for low cost single axis tracking systems.
