Long-Term Thermal Stability of Liquid Dye Solar Cells

Abstract

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.

Consequences of Solid Electrolyte Interphase (SEI) Formation upon Aging on Charge-Transfer Processes in Dye-Sensitized Solar Cells

“…Such evolution has been noted previously in the literature on complete devices but without extensive explanation. [15][16][17] We attribute this interfacial electrochemical modification of Pt/electrolyte characteristic to the formation of SEI surrounding the platinum nanoparticles during ageing.…”

“…devices. 17 Because the SEI contains a relatively high concentration of charged and polar species (eg. I -, I3 -, NCS -, Gu + , polyacrylonitrile and probably other degradation byproducts from electrolyte) neither of these processes would be surprising.…”

Cobalt-Based Electrolytes for Dye-Sensitized Solar Cells: Recent Advances towards Stable Devices

“…typically gives a negative shift of the TiO2 conduction band, and reduced interfacial recombination losses are observed, resulting in a relatively higher Voc [45]. It is quite surprising to find only very few papers addressing the influence of these additives on the durability of cobalt-based DSCs, despite an extensive literature being found for the iodide/triiodide redox mediator [46][47][48][49], also taking into account the role of different counterions [50,51]. Only recently, Gao et al have reported that higher concentrations of the cobalt-based redox components, in both the reduced and, surprisingly, the oxidized forms, offer improved long-term stability with the limited drawback of a lower initial PCE [52].…”

A Review on Current Status of Stability and Knowledge on Liquid Electrolyte-Based Dye-Sensitized Solar Cells

“…They have concluded that iodine depletion is significantly hampered when going from -butyrolactone to HSS. They have also reported slower iodine consumption using tetraglyme compared to 3-MPN [156].…”

“…This has been clearly highlighted from the work led at Dyesol by Jiang et al [132,156]. The authors compared -butyrolactone, 3-methoxypropionitrile, and the socalled nitrile-free solvent HSS.…”