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 TiO2 and noninjecting ZrO2. 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 TiO2 near 900 nm for all cells, existing from 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 publicatio...