Mechanisms and kinetics of electron injection in dye-sensitized solar cells

Electron injection in dye-sensitized solar cells (DSSC) has been extensively studied in the present thesis. Many transient and steady-state experimental techniques were utilized: ultrafast transient absorption spectroscopy in the visible, near-IR and mid-IR regions; time-correlated single photon counting; incident photon to current conversion measurement; temperature dependence of luminescence and device efficiency; determination of energy conversion efficiency parameters. All these methods were collated and analysed as a whole, providing a very detailed picture of the electron injection. It was found that in devices utilizing the most efficient Ru-bipyridyl dyes and commercially viable, performance optimized iodine/triiodide electrolytes, electron injection kinetics are multiphasic, with significant components in the femtosecond, tens of picoseconds and in nanosecond regimes. The broad non-exponential kinetics gave rise to non-100% efficient injection. A fraction of the dyes manage to decay giving rise to luminescence. All of these observations were fully quantified and validated by performing measurements on different systems. The huge length of the delay lines in TAS measurements and very broad probe wavelengths used in the current work gave a very detailed picture of the injection process. Along the way, some very basic experiments were done, which added confidence to the results obtained in the thesis. In addition, interesting phenomena occurring in the ultrafast timescales were found and spectra of transient species such as the dye excited states were recorded. Finally, relevance of the current work to the practical aspects of the solar cells was described and future work discussed.Open Acces