Final Report Summary - SINGFISS (Singlet exciton fission as a route to more efficient dye-sensitized solar cells)
One of the major loss mechanisms in current solar cell technology is related to inefficient use of light in the range where the energy per photon is very high, for instance ultra-violet light. Absorption of such photons generally leads to the excitation of one electron, and all the excess energy available in the high-energy photons is lost as heat. Singlet exciton fission is a process in which this energy loss is circumvented by using the excess energy to excite a second electron, hence doubling the amount of electrons that can be used as electrical current. Overall, singlet fission can increase the efficiency of plastic solar cells by a factor of 1.5. In the research performed in this project, a thorough fundamental study of singlet fission was performed using a variety of techniques, ranging from computer simulations and organic synthesis to state-of-the-art ultrafast spectroscopy. These studies have revealed that the efficiency of singlet fission is strongly dependent on the organisation of molecules in the solid state. Taking a series of very similar molecules with minor modifications it was shown that very subtle changes in the packing of the molecules in the crystal can lead to large changes in the singlet fission efficiency. The results obtained here indicate some very general guidelines for the design of materials in which singlet fission occurs efficiently and new materials can be developed using these guidelines. Ultimate, this will lead to new materials that exploit singlet fission to create organic solar cells which a greatly improved efficiency.