XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Singlet Fission for Dye-Sensitized Solar Cells
Zdenek Havlas1, Josef Michl1,2
1Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2, 16610 Prague6, Czech Republic
2Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States
Singlet Fission is a spin-allowed process in which a molecular chromophore excited into its singlet state shares energy with a nearby ground state chromophore, producing a pair of triplet excited
chromophores initially coupled into an overall singlet. In a more detailed description, the initial singlet state actually is a coherent superposition of eigenstates of the total Hamiltonian operator that includes electron spin-spin and Zeeman interactions that dictate its further fate, along with possible spatial diffusion, internal conversion, intersystem crossing, and other possible competing processes.
Although, the Singlet Fission is known is some special cases of crystalline aromatic hydrocarbons for a half of century, using of this process for increasing of the solar cell efficiency is a new topic. It includes studies of several steps and interplay of theoretical, synthetic, and spectroscopic procedures, namely:
- Selection of the proper chromophore which satisfies the following conditions: E(S1) ≥ 2 E(T1) but also E(T2) ≥ 2 E(T1). We have observed that 1,3-diphenyl-isobenzofuran satisfies these conditions and yields 200% of triplet states in a crystalline state.
- For practical reasons, the S1 excitation energy should be around 2.2 eV. Searching for structures with this property is done by extensive set of quantum chemical calculations of excited states. We have already preselected a few structures which have to be now synthesized and studied experimentally.
- For effective Singlet Fission process proper mutual orientation of chomophore pairs is essential. We have developed a simple Hamiltonian model and performed numerical calculations for different orientations of chromophores. The rules for the geometrical requirements resulted from these calculations will be discussed.
- Preparation of a dye with both chromophores in ideal positions, either by self-organization or by synthesis of supermolecule with both chromophores properly arranged in it.
- The final stage requires separation of charges of individual triplet chromophores, transport of the charges to the TiO2 semiconductor and injection of the electrons to the semiconductor.
We will report on progress in the first three steps, the last two steps still need to be solved.


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