ABSTRACT
Sensitizer dyes capable of producing two triplet excited states from a singlet excited state produced by the absorption of a single photon would allow an increase of the efficiency of photovoltaic cells by up to a factor of 1.5, provided that each triplet injects an electron into a semiconductor such as TiO2. Although singlet fission (SF) in certain crystals and polymers was reported long ago, little is known about its efficiency in dyes suitable for use as sensitizers of photo-induced charge separation on semiconductors surfaces. In the present project, we have accomplished the following, in collaboration with Prof. A. J. Nozik at National Renewable Energy Laboratory (NREL) and with a subcontractor, Prof. M. A. Ratner at Northwestern University:
1. A theoretical analysis and a series of computations established that biradicaloids and alternant hydrocarbons are likely parent structures for meeting the exothermicity requirement E(T2), E(S1) > 2E(T1) for the excitation energies of the lowest excited singlet (S1) and the two triplet (T1, T2) states.
