  The photosystem II reaction centre is the photosynthetic complex responsible
for oxygen production on Earth. Its water splitting function is particularly
favoured by the formation of a stable charge separated state via a pathway that
starts at an accessory chlorophyll. Here we envision a photovoltaic device that
places one of these complexes between electrodes and investigate how the mean
current and its fluctuations depend on the microscopic interactions underlying
charge separation in the pathway considered. Our results indicate that coupling
to well resolved vibrational modes does not necessarily offer an advantage in
terms of power output but can lead to photo-currents with suppressed noise
levels characterizing a multi-step ordered transport process. Besides giving
insight into the suitability of these complexes for molecular-scale
photovoltaics, our work suggests a new possible biological function for the
vibrational environment of photosynthetic reaction centres, namely, to reduce
the intrinsic current noise for regulatory processes.
