  We study linear response and nonequilibrium steady-state thermoelectric
transport through a single-level quantum dot tunnel coupled to two reservoirs
held at different temperatures as well as chemical potentials. A fermion
occupying the dot interacts with those in the reservoirs by a short-ranged
two-particle interaction. For parameters for which particles flow against a
bias voltage from the hot to the cold reservoir this setup acts as an
energy-conversion device with which electrical energy is gained out of waste
heat. We investigate how correlations affect its efficiency and output power.
In linear response the changes in the thermoelectric properties can be traced
back to the interaction induced renormalization of the resonance line shape. In
particular, small to intermediate repulsive interactions reduce the maximum
efficiency. In nonequilibrium the situation is more complex and we identify a
parameter regime in which for a fixed lower bound of the output power the
efficiency increases.
