Probing Dye-Correlated Interplay of Energetics and Kinetics in Mesoscopic Titania Solar Cells with 4-tert-Butylpyridine

The adsorption of 4-tert-butylpyridine (TBP) on the surface of oxide semiconductors can tune their interband state distributions as well as the conduction band edges, offering a straightforward tactic to modulate the energy alignments at the titania/dye/electrolyte interface in dye-sensitized solar cells. In this work, by stepwise augmenting the TBP concentration in electrolytes, we investigate the energetic and kinetic interplays in mesoscopic titania solar cells based upon two push pull organic dyes C218 and D205. TBP at a higher concentration, while better retarding triiodide interception of photoinjected electrons in C218 cells, has strikingly induced an acceleration of interfacial charge recombination with triiodide in devices employing the D205 dye, accounting for a much smaller photovoltage enhancement with respect to the C218 counterpart. Transient emission measurements disclose that the exciton dissociation at the titania/C218 dye interface does not noticeably vary despite a TBP-correlated conduction band edge elevation, which has otherwise prompted an evident Gibbs free-energy-dependent rate of electron injection in cells based on the D205 photosensitizer.