  We discuss the key principles of artificial photosynthesis for photovoltaic
energy conversion. We demonstrate these principles by examining the operation
of the so-called "dye sensitized solar cell" (DSSC) - a photoelectrochemical
device which simulates the charge separation process across a nano-structured
membrane that is characteristic of natural systems. These type of devices have
great potential to challenge silicon semiconductor technology in the low cost,
medium efficiency segment of the PV market. Ruthenium charge transfer complexes
are currently used as the photon harvesting components in DSSCs. They produce a
relatively broad band UV and visible response, but have long term stability
problems and are expensive to manufacture. We suggest that a class of
biological macromolecules called the melanins may be suitable replacements for
the ruthenium complexes. They have strong, broad band absorption, are
chemically and photochemically very stable, can be cheaply and easily
synthesized, and are also bio-available and bio-compatible. We demonstrate a
melanin-based regenerative solar cell, and discuss the key properties that are
necessary for an effective broad band photon harvesting system.
