Concept
Light harvesting materials harvest solar energy that can then be converted into chemical energy through photochemical processes. Synthetic light harvesting materials are inspired by photosynthetic biological systems such as light harvesting complexes and pigments that are present in plants and some photosynthetic bacteria. The dynamic and efficient antenna complexes that are present in photosynthetic organisms has inspired the design of synthetic light harvesting materials that mimic light harvesting machinery in biological systems. Examples of synthetic light harvesting materials are dendrimers, porphyrin arrays and assemblies, organic gels, biosynthetic and synthetic peptides, organic-inorganic hybrid materials, and semiconductor materials (non-oxides, oxynitrides and oxysulfides ). Synthetic and biosynthetic light harvesting materials have applications in photovoltaics, photocatalysis, and photopolymerization. During photochemical processes employing donor and acceptor chromophores in organic solar cells, a photon is absorbed by the donor and an exciton is generated. The exciton diffuses to a donor/acceptor interface, or heterojunction, where an electron from the lowest unoccupied molecular orbital (LUMO) of the donor is transferred to the LUMO of the acceptor. This results in the formation of electron-hole pairs. When the photon is absorbed by the acceptor and the exciton reaches a heterojunction, an electron will then transfer from the HOMO of the donor to the HOMO of the acceptor. In order to make certain there is effective charge transfer, the continuous donor or acceptor domains must be smaller than the exciton diffusion length (< ~0.4 nm). The light harvesting efficiency of energy transfer in light harvesting materials can be enhanced by either decreasing the distance between the donor and acceptor or designing a material that contains multiple antenna chromophores per acceptor (antenna effect).