The synthesis of efficient metal-free NIR sensitizers remains as one of the more challenging aspects for dye-sensitized solar cell (DSC) researchers. We report four NIR photosensitizers employing a thieno[3,4-b]thiophene (3,4-TT) π-bridge and a heavily alkylated donor for use in DSCs. The inclusion of furan or thiophene π-spacers was found to significantly narrow the optical band gap to allow solution absorption onsets reaching 700 nm. Cyclic voltammetry and UV-Vis-NIR absorption spectroscopy confirmed these photosensitizers possess suitable energy levels for electron transfer in DSC devices. Additionally, computational studies imply good orbital distribution for charge transfer across the dyes with sufficient spatial separation of frontier orbitals to suppress back electron transfer in devices. Computationally optimized ground-state geometries of a dye incorporating an alkylated π-spacer show an increased torsional angle between π-spacer and π-bridge. This decrease in planarity diminished the overall charge transfer between donor and acceptor moieties, resulting in a slightly widened optical band gap and de-stabilized oxidation potentials relative to a non-alkylated π-spacer analogue in solution. However, the alkylated and non-alkylated π-spacer exhibited nearly identical incident photon-to-current conversion efficiency curve onsets, suggesting the added torsional strain introduced through the alkylated π-spacer was suppressed on the TiO<sub>2</sub> surface. Dyes utilizing π-spacers generated lowered short-circuit current densities despite wider IPCE spectra presumably due to lowered excited-state oxidation potentials leading to sluggish electron injection. However, a bolstered open-circuit voltage generated by alkylated π-spacer dye-based devices. Overall, power conversion efficiencies up to 6.8% and IPCE onsets up to 800 nm were observed.<br/>

Panchromatic photoresponsive dye-sensitized solar cell devices using thieno[3,4-b]thiophene-based photosensitizers

255th National Meeting (2018)

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