Evidence for “Slow” Electron Injection in Commercially Relevant Dye-Sensitized Solar Cells by vis–NIR and IR Pump–Probe Spectroscopy

Abstract

We present femtosecond to nanosecond transient absorption (TA) data on electron injection in dye-sensitized solar cells (DSSCs) fabricated with low volatility, commercially relevant electrolytes, with and without added lithium. Results are shown over an extended time range (300 fs−6.3 ns) and extended wavelength range (800−1400 nm) for both N719 and C106 dyes. Kinetics were measured on both TiO 2 and noninjecting ZrO 2 . Using the latter, we have determined the spectra and absorption coefficient of N719* across the wavelength range. We find an isosbestic point in the TA spectra on TiO 2 near 900 nm for all cells, existing from <1 ps to >1 ns. We show how measurements near this isosbestic point can give a false impression of uniformly femtosecond injection dynamics in DSSCs. Comparison of dynamics measured at 1200 nm with mid-IR transient absorption measured at 5100 nm confirms a majority proportion of slow (>10 ps) electron injection in these commercially relevant cells. We also comment on a recent publication which appears to directly contradict the results we present.

Electron injection dynamics in dye-sensitized semiconductor nanocrystalline films

“…Slow electron injection was observed in monolayer dye sensitized TiO 2 by Sundstrom group [43]. Most recently, slow electron injection in commercially relevant dyesensitized solar cells by vis-NIR and IR pump-probe Spectroscopy has been reported and the measurement condition is pointed out to be important [52].…”

“…For the electron injection from the triplet state inter-ligand electron transfer process was investigated as one of the reasons of the slow reaction [38]. Some other groups have published many papers in order to understand the important electron injection process in DSSC [44][45][46][47][48][49][50][51][52].…”

The Impact of the Electrical Nature of the Metal Oxide on the Performance in Dye-Sensitized Solar Cells: New Look at Old Paradigms

“…6 On the other hand, photoanodes prepared with ZnO have been studied as an alternative to TiO 2 . [13][14][15][16][17][18][19] All of the above issues have been addressed in this contribution. 7 Time-resolved laser spectroscopy has been widely applied to study the primary steps in charge separation in DSSCs, especially for those based on Ru compounds.…”

Performance Evaluation of Titanate Nanotubes and Nanoribbons Deposited by Electrophoresis in Photoelectrodes of Dye-Sensitized Solar Cells

“…In the DSSC field, it is one of the most useful experimental techniques, as it permits a simultaneous characterization of the different processes taking place on the cell 25,26 . A key attractive feature is its application on full solar cell devices and the indication of the main limitations of the cell photoelectrical performance.…”