Broad Band Photon Harvesting Biomolecules for Photovoltaics

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.