Laboratory-size dye
solar cells (DSCs), based on industrially feasible
materials and processes employing liquid electrolytes, have been developed.
Cells based on two electrolyte solvents with different physical properties
were subjected to thermal stress test at 80 °C for 2000 h in
the dark to monitor their long-term thermal stability. The DSCs incorporating
a methoxypropionitrile (MPN)-based electrolyte presented a severe
efficiency loss at 1 sun AM 1.5G of more than 70% upon thermal aging,
while the solar cells using tetraglyme (TG) as a high boiling point
solvent attained a promising stability with only 20% loss of performance.
To better understand the above behavior, systematic experiments, including
optical microscopy, linear sweep voltammetry, UV–vis absorption,
electrochemical impedance, and Raman spectroscopies were conducted.
Virtually no dye degradation/desorption, electrolyte decomposition,
semiconductor passivation, or loss of cathode activity could be identified.
For the MPN-based cells, a sharp decrease in the short-circuit photocurrent
was observed at high illumination intensities following thermal stress,
attributed to charge-transfer limitations due to severe triiodide
loss, verified by different experimental techniques. These degradation
effects were efficiently mitigated by replacing MPN with the high-boiling-point
solvent in the electrolyte