The reaction centres of photosynthetic organisms are undoubtedly the most sophisticated examples of photochemical energy conversion systems. They have inspired chemists to synthesise artificial photosynthetic systems, such as molecular donor / acceptor systems and light harvesting arrays capable of emulating at least key elements of their function. In parallel with these advances in artificial photosynthesis, attention has increasingly turned to the possibility of fabricating photovoltaic solar cells based upon molecular or polymer light absorbers. Molecular based solar cells offer the potential for efficient solar energy conversion using low cost materials and fabrication techniques1. Significant progress is now being made towards the commercial production of such devices for specific market applications. However at present the efficiencies and durabilities of molecular and polymer based devices remain modest in comparison to silicon based solar cells, and much research and development work remains to be undertaken before such devices can effectively compete with silicon devices for large scale solar energy conversion.
In this paper, I will focus upon the light driven charge separation which underlies the function of molecular based photovoltaics. Issues I will try to cover will include:
• A comparison of the parameters determining charge separation in dye sensitised, bilayer and bulk heterojunction solar cells
• Thermodynamic versus kinetic control of charge separation
• Limits to energy storage efficiency
• Overcoming the coulomb attraction of photogenerated charges.

1. Durrant, JR, Haque, SA, Palomares, E, Photochemical energy conversion: from molecular dyads to solar cells, Chem. Comm., 2006, 3279 – 3289.