  Heat engines cannot generally operate at maximum power and efficiency,
imposing a trade-off between the two. Here, we highlight the exact nature of
this trade-off for engines that exchange heat radiatively with a hot source. We
derive simple analytical expressions for the performance bounds of reciprocal
and nonreciprocal radiative heat engines. We also highlight that radiative
engines can achieve a better power-efficiency trade-off than linear ones. These
bounds are especially relevant for thermophotovoltaics, offering useful metrics
against which to compare device performance.
