Photoinduced electron transfer from a molecular chromophore into mesoporous metal oxide substrates occurs efficiently from both singlet and triplet excited states for traditional metal-to-ligand charge transfer (MLCT) dyes. All-organic molecules that undergo singlet fission (SF), the process of generating two triplet excitons with photoexcitation of one singlet exciton, offer a promising method of generating two charges per one absorbed photon. However, the singlet-triplet energy balance required to drive SF often places the driving force for triplet electron injection into metal oxides too low. As such, the dynamics of singlet vs. triplet electron transfer for SF in dye-sensitized solar cell configurations has not been elucidated. Here, we use applied bias transient absorption spectroscopy to modulate the driving force for triplet electron transfer for an anthradithiophene-based SF chromophore (<b>ADT-COOH</b>) adsorbed to mesoporous indium tin oxide (<i>nanoITO</i>). Observing the electron injection rate constant across a range of potential shows an acceleration of triplet electron injection at driving forces greater than -0.6 eV. There is a distinct trend observed with increasing applied bias that matches Marcus theory predictions for electron transfer for a distribution to acceptor states.

Resolving electron injection from singlet fission-borne triplets into mesoporous transparent conducting oxides

ACS Spring 2022

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