10.1021/jp4125364.s001 Andreas F. Bartelt Andreas F. Bartelt Robert Schütz Robert Schütz Christian Strothkämper Christian Strothkämper Joachim Schaff Joachim Schaff Stephan Janzen Stephan Janzen Paja Reisch Paja Reisch Ivo Kastl Ivo Kastl Manuel Ziwritsch Manuel Ziwritsch Rainer Eichberger Rainer Eichberger Gerda Fuhrmann Gerda Fuhrmann David Danner David Danner Lars-Peter Scheller Lars-Peter Scheller Gabriele Nelles Gabriele Nelles Efficient Electron Injection from Acyloin-Anchored Semisquarylium Dyes into Colloidal TiO<sub>2</sub> Films for Organic Dye-Sensitized Solar Cells American Chemical Society 2014 indoline dye D 131 semisquarylium dye SY 404 TiO 2 surface electron injection properties carboxylic acid nanocrystalline TiO 2 novel acyloin anchor group TiO 2 semiconductors Efficient acyloin anchor carboxylic acid anchor group semisquarylium dyes semisquarylium dye DD 1 Efficient Electron Injection acyloin anchor TiO 2 conduction band SY 404 dye Colloidal TiO 2 Films IPCE 2014-04-03 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Efficient_Electron_Injection_from_Acyloin_Anchored_Semisquarylium_Dyes_into_Colloidal_TiO_sub_2_sub_Films_for_Organic_Dye_Sensitized_Solar_Cells/2309602 Semisquarylium dyes use a novel acyloin anchor group to strongly bind to TiO<sub>2</sub> semiconductors. Efficient acyloin anchor mediated electron injection into nanocrystalline TiO<sub>2</sub> is demonstrated, allowing highly efficient dye-sensitized solar cells with IPCEs > 80%. The acyloin anchor can thus be viewed as a true alternative to the standard carboxylic acid anchor group. The opto-electronic and electron injection properties of the most basic semisquarylium dye <b>SY404</b> are compared to the modified semisquarylium dye <b>DD1</b> and the carboxylic acid anchored indoline dye <b>D131</b> using a combination of ultrafast and photoemission spectroscopy. For <b>SY404</b>, ultrafast injection times of ∼50 fs are found despite a small energetic driving force between dye excited states and TiO<sub>2</sub> conduction band minimum. This is possible due to the strong electronic coupling of the semisquarylium dyes to the TiO<sub>2</sub> surface mediated by the acyloin anchor. For a better overlap with the solar spectrum, the semisquarylium dyes are modified by substitution with a larger donor moiety (<b>DD1</b>). While for <b>DD1</b> the overall absorption increases, the injection process slightly slows down; however, it still proves fast enough for very efficient injection. Compared to the carboxylic acid anchored indoline dye <b>D131</b>, the <b>SY404</b> dye injects more than seven times faster despite a ∼150 meV smaller driving force.