Photoelectrochemical
devices could play a crucial role toward fuel
production in a circular economy. Yet, light absorption suffers losses
from thermalization and the inability to use low-energy photons. Here,
we demonstrate that photoelectrochemical reactors can utilize this
waste heat by integrating thermoelectric modules, which provide additional
voltage under concentrated light irradiation. While most single semiconductors
require external bias, we already accomplish unassisted water splitting
under 2 sun irradiation by wiring a BiVO4photoanode to
a thermoelectric element, whereas the photocurrent of a perovskite-BiVO4tandem system is enhanced 1.7-fold at 5 sun. This strategy
is particularly suitable for photoanodes with more positive onset
potentials like hematite, with thermoelectric-perovskite-Fe2O3systems achieving a 29.7× overall photocurrent
increase at 5 sun over conventional perovskite-Fe2O3devices without light concentration. This thermal management
approach provides a universal strategy to facilitate widespread solar
fuel production, as light concentration increases output, reduces
the reactor size and cost, and may enhance catalysis.