Dynamics of local Stark effect observed for a complete D149 dye-sensitized solar cell

A complete, functioning dye-sensitized solar cell made of popular indoline D149 sensitizer is studied by means of transient absorption in visible light in the time scale of nanoseconds to seconds. Photocurrent and photovoltage decays are also measured under the same experimental conditions. A local electric field causing a Stark shift of the D149 absorption band is found to strongly influence the transient spectra and kinetics. The presence of electrons in titania has a major contribution to the Stark shift and the effect disappears over many time scales with an average rate of 5 x 10(3) s(-1). This is much slower than the decay of the oxidized dye (2 x 10(6) s(-1)) but, on the other hand, significantly faster than the decay of electrons in titania nanoparticles (3 x 10(2) s(-1) at standard AM1.5 irradiation and open circuit conditions). Possible explanations of this phenomenon are discussed. Electron recombination from the titania conduction band to the oxidized dyes proceeds at an average rate of 2-16 x 10(4) s(-1), depending on the excitation energy density, and does not influence the efficiency of dye regeneration.