  Manipulating the flow of energy in nanoscale and molecular photonic devices
is of both fundamental interest and central importance for applications in
light harvesting optoelectronics. Under erratic solar irradiance conditions,
unregulated power fluctuations in a light harvesting photocell lead to
inefficient energy storage in conventional solar cells and potentially fatal
oxidative damage in photosynthesis. Here, we show that regulation against these
fluctuations arises naturally within a two-channel quantum heat engine
photocell, thus enabling the efficient conversion of varying incident solar
spectrum at Earth's surface. Remarkably, absorption in the green portion of the
spectrum is avoided, as it provides no inherent regulatory benefit. Our
findings illuminate a quantum structural origin of regulation, provide a novel
optoelectronic design strategy, and may elucidate the link between
photoprotection in photosynthesis and the predominance of green plants on
Earth.
