  Irreversible effects in thermoelectric materials limit their efficiency and
economy for applications in power generation and refrigeration. While electron
transport is unavoidably irreversible in bulk materials, here we derive
conditions under which reversible diffusive electron transport can be achieved
in nanostructured thermoelectric materials via the same physical mechanism
utilized in quantum optical heat engines. Our results may provide a physical
explanation for the very high efficiencies recently reported for nanostructured
thermoelectric materials such as quantum-dot superlattices.
