Dynamics of Singlet Fission in Tetracene and Triplet Transfer to Silicon

The photovoltaic efficiency of Si solar cells can be enhanced beyond the Shockley-Queisser limit by adding an organic singlet fission layer. The high energy photons are absorbed in the organic layer to create a singlet exciton, which splits into two triplet excitons via singlet fission. The challenge is to harvest the triplets with Si. The triplets should diffuse to the interface where both charge and energy transfer to Si are possible.

We study the efficiency of singlet fission, triplet diffusion, charge and energy transfer to Si by a combination of time-resolved spectroscopic techniques with optical and microwave/terahertz conductivity measurements. We are using tetracene as a singlet fission layer because the triplet energy (~1.25eV) is larger than the Si band-gap (~1.1eV), therefore energy transfer from the triplets to Si is energetically favorable. The singlet decay and triplet formation is monitored through transient absorption spectroscopy as both the singlet and triplet have distinct characteristics in the transient spectra. The initial findings suggest that the singlet fission occurs efficiently. However, the triplet transfer process to Si will significantly depend on the nature of Si surface and orientation of tetracene on Si. Therefore, particular attention is paid to the nature of the Si surface and coupling of functionalized tetracene to the Si surface. Results of the effects of the abovementioned parameters on the efficiency of energy/charge transfer from the singlet fission layer to Si will be presented.