Skip to Main Content
The solar energy is an alternative source of renewable energy. The current inorganic solar cells mostly based on amorphous Si have been able to provide an efficiency of 10 - 20% for solar energy conversion. Organic solar cells have been proposed as another alternative mostly due to the high quantum efficiency of solar power conversion seen in natural world. They offer the possibility for lighter-weight and environmentally clean renewable energy sources. We present a firstprinciples study on a bio-mimetic light harvesting organic. This 207-atom molecular triad consists of a fullerene, a porphyrin and a carotenoid. In order to simulate this energy conversion it is necessary to determine the transition rates from density functional theory and then use a Monte-Carlo approach to simulate the photon induced charge-separation process. Charge transfer excited states have been calculated using a new density-functional based method. We have used NRLMOL and honey-bee algorithms to perform the electronic structure calculations on the NRL SGI-Altix system. The Monte-Carlo simulations have used a coarse grained approach in which many different starting conditions are studied on individual processors. We find that the molecule possesses a dipole moment of 180D in the charge-separated state. We show that an electric field and incident solar radiation are necessary for excitation into a charge-separated state. The necessary electric field can be realized through a solvated ionic solution or in the crystalline phase. Such excitation of one molecule in solution can quickly trigger a dipolar-induced cascade process leading to aligned chains and possibly solarinduced current.