Photocathodes Beyond NiO – Charge Transfer Dynamics in a π-Conjugated Polymer Functionalized with Ru Photosensitizers

in: Scientific Reports (2021)
Wahyuono, Ruri Agung; Seidler, Bianca; Bold, Sebastian; Dellith, Andrea; Dellith, Jan; Ahner, Johannes; Wintergerst, Pascal; Lowe, Grace; Hager, Martin D.; Wächtler, Maria; Streb, Carsten; Schubert, Ulrich S.; Rau, Sven; Dietzek, Benjamin
A conductive polymer (poly(p-phenylenevinylene), PPV) was covalently modified with RuII Complexes to develop an all-polymer photocathode as a conceptual alternative to dye-sensitized NiO, which is the current state-of-the-art photocathode in solar fuels research. Photocathodes require efficient light-induced charge-transfer processes and we investigated these processes within our photocathodes using spectroscopic and spectro-electrochemical techniques. Ultrafast hole-injection dynamics in the polymer were investigated by transient absorption spectroscopy and charge transfer at the electrode–electrolyte interface was examined with chopped-light chronoamperometry. Light-induced hole injection from the photosensitizers into the PPV backbone was observed within 10 ps and the resulting charge-separated state (CSS) recombined within ~ 5 ns. This is comparable to CSS lifetimes of conventional NiO-photocathodes. Chopped-light chronoamperometry indicates enhanced charge-transfer at the electrode–electrolyte interface upon sensitization of the PPV with the RuII complexes and p-type behavior of the photocathode. The results presented here show that the polymer backbone behaves like classical molecularly sensitized NiO photocathodes and operates as a hole accepting semiconductor. This in turn demonstrates the feasibility of all-polymer photocathodes for application in solar energy conversion.

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