Investigation of Ethylisopropyl Sulfone Medium with a Copper-Based Redox Electrolyte for Ambient Light Dye-Sensitized Solar Cells: Achieving High Efficiency and Enduring Long-Term Stability

Abstract

In recent years, dye-sensitized solar cells (DSCs) have shown remarkable efficiency levels, particularly under low light conditions, making them promising candidates for indoor applications. However, for these devices to be successfully commercialized, high power conversion efficiencies (PCEs) alone are not sufficient. Long-term stability is a critical aspect that needs to be addressed. Most of the well performing DSCs reported so far have utilized conventional organic solvents, which have low boiling points and are highly volatile. While these solvents contribute to achieving high PCE values, they are prone to leakage and evaporation, limiting the long-term stability of the devices. Herein, we report on cosensitized DSC devices (A−E) with commercial dyes (XY1b/MS5) and different additives. This was accomplished by employing for the first time ethylisopropyl sulfone (EiPS) as a high boiling point solvent along with Cu (I) (dmby) 2 •TFMSI and Cu (II) (dmby) 2 Cl•TFMSI as the redox mediators in DSCs. Remarkably, most of the tested DSC devices exhibited exceptional performance, achieving high PCE values ranging from 19% to 23% under 1000 lx irradiation and up to 0.82% under 1 sun simulated solar light irradiation. Our analysis revealed that the N-methylbenzimidazole (NMBI) additive played a crucial role in ensuring both good PCE% and long-lasting durability, particularly in device B. On the other hand, the use of additives such as 1-butyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide (ImTFMSI) and/or LiTFMSI resulted in deterioration of the photovoltaic parameters during the long-term stability tests in the EiPS-based electrolyte medium, observed in devices C−E. This knowledge opens up possibilities for further optimization of ambient-light DSCs with improved stability and provides a viable solution for indoor power generation applications.

Copper-Based Aqueous Dye-Sensitized Solar Cell: Seeking a Sustainable and Long-Term Stable Device

“…The efficiency substantially increased to 9.19% upon the addition of a Lewis base, N -methylbenzimidazole (NMBI), to their electrolyte system. In addition, our laboratory recently reported a similar finding with a copper-based electrolyte system in ethyl isopropyl sulfone (EiPS) under low light conditions . In that case, the DSSC’s PCE % increased from 3.2 to 19.3% under 1000 lx illumination upon the addition of 0.6 M NMBI to the copper electrolyte in EiPS.…”

“…Various research groups have reported similar findings supporting the notion of Cu II coordination. They have obtained results analogous to those presented above, indicating negative shifts in the E 1/2 values for Cu II (dmp) 2 +2 (dmp = 2,9-dimethyl-1,10-phenanthroline) upon the addition of Lewis bases such as 4- t -butylpyridine (TBP) or NMBI. ,,, Moreover, Freitag et al have shown that the rest potentials of Cu I/II (dmp) 2 +2 and Cu I/II (tmby) 2 +2 (tmby = 4,4′,6,6′- tetramethyl-2,2′-bipyridine) differ significantly from the formal redox potentials derived from CV experiments in ACN (less by ∼0.25 V for the former) depending on the counter-ion identity and any Lewis base presence . Interestingly, the rest potentials of our different electrolytes shifted slightly to more negative values with increasing [HNMBI + OAc – ] (less by ∼40 mV for E5 than E0 ) (Table ).…”

“…First, as a buffering agent, it helped to maintain a slightly acidic pH, thus preventing dye desorption over time. Second, it served as a source of the free Lewis base, NMBI, which plays a crucial role in copper-based DSSCs, as observed in the aforementioned study and other published reports. ,− The a-DSSCs were tested at different concentrations of HNMBI + OAc – in the electrolyte ( E0 to E6 ) under both ambient light and 1 Sun irradiation intensities. The results elucidated that the performance of a-DSSC is influenced by the presence of the HNMBI + OAc – additive, specifically by the amount of free NMBI derived from the additive.…”

“…In that case, the DSSC’s PCE % increased from 3.2 to 19.3% under 1000 lx illumination upon the addition of 0.6 M NMBI to the copper electrolyte in EiPS. Therefore, recognizing the apparent significant role of NMBI in copper-based electrolyte systems from the mentioned studies, ,− we decided to incorporate it as an additive in our aqueous electrolyte medium. However, to prevent the risk of dye desorption from TiO 2 in alkaline aqueous media upon the addition of NMBI, we opted to use the water-soluble N -methylbenzimidazolium acetate (HNMBI + OAc – ) as an alternative additive in the aqueous electrolyte (Scheme ).…”

“…Recently, our research group reported, for the first time, on an a-DSSC based on a water-soluble and Lewis-base free copper redox couple, [Cu I (dc-dmby) 2 /Cu II (dc-dmby) 2 (where dc-dmby = 6,6′-dimethyl-2,2′-bipyridine-4,4′-dicarboxylate)], in conjunction with a hydrophobic ruthenium-based sensitizer, C106, that achieved a PCE % of ∼7% under ambient light conditions . However, recent reports showed the importance of Lewis-base additives, such as N -methylbenzimidazole (NMBI) and t -butylpyridine (TBP), in copper-based electrolyte systems. ,− Such additives are believed to be involved in the Cu II coordination as fifth/sixth ligand (s), enhancing the metal complex regeneration at the counter electrode, retarding electron recombination, and/or negatively shifting the redox potential of the electrolyte system, thus enhancing dye regeneration.…”