High boiling point solvent-based dye solar cells pass a harsh thermal ageing test

Dye solar cells (DSCs) have emerged as one of the most efficient third-generation photovoltaic (PV) technologies, whose commercialization is mainly hampered by the lack of sufficient long-term stability compared to conventional PV devices. In this work, it is demonstrated that solvent based DSCs using tetraglyme as a non-nitrile, high boiling point, organic solvent for the iodide/triiodide redox shuttle, can pass a harsh accelerated thermal ageing test of 3000 h light soaking followed by additional 2000 h thermal ageing at 85 °C. Electrochemical and spectroscopic analysis on thermal degradation effects revealed that a conduction band edge shift towards more negative potentials for tetraglyme-DSCs underlies the enhanced photopotential of aged cells, compensating for the thermally induced photocurrent reduction due to slight triiodide loss. The tetraglyme-based solar cells (in contrast to cells based on methoxypropionitrile-MPN) showed exceptional stability, compatible with the established IEC61646 protocol for thin film PVs, keeping ca. 90% of their initial performance under 1 sun illumination. Quite notably, the cells even increased their initial efficiency by 4% when illuminated under 0.1 sun. This is the first time in literature that such a stability record is accomplished for solvent based DSCs utilizing commercially available and cost-effective materials. © 2015 Elsevier B.V. All rights reserved

Thermal Stressing of Dye Sensitized Solar Cells Employing Robust Redox Electrolytes

Robust Dye Sensitized Solar Cells have been prepared employing liquid electrolytes using ethyl isopropyl sulfone (EiPS) high boiling point solvent. The cells were tested for their durability under harsh thermal stressing conditions of 85 °C and prolonged ageing time, 3000 h in the dark. The use of EiPS outperforms stability-wise the typical methoxypropionitrile MPN solvent, improving the cell stability from 38 to 75%. For both solvents, the physicochemical analysis infers the thermal degradation of the cell with the main changes occurring in the first 300 h of ageing. This was attributed to partial triiodide loss which reduces short circuit photocurrent and leads to formation of luminescent species in the electrolyte that affects the TiO2 surface and reduces open circuit photovoltage. The degradation effects were notably supressed by the use of the more stable EiPS solvent, where it was possible to optimize the iodine content in the redox mediator. It has been thus confirmed that iodine concentration as low as 0.05 M in the EiPS electrolyte is slightly preferable in terms of stability and device performance, comparing with higher concentrations, 0.1 and 0.15 M, respectively. © 2015 Elsevier Ltd. All rights reserved

In Situ Raman Study of Nickel Oxide and Gold-Supported Nickel Oxide Catalysts for the Electrochemical Evolution of Oxygen

An in situ Raman spectroscopic investigation has been carried out to identify the composition of the active phase present on the surface of nickel electrodes used for the electrochemical evolution of oxygen. The electrolyte in all cases was 0.1 M KOH. A freshly polished Ni electrode oxidized upon immersion in the electrolyte and at potentials approaching the evolution of oxygen developed a layer of γ-NiOOH. Electrochemical cycling of this film transformed it into β-NiOOH, which was observed to be three times more active than γ-NiOOH. The higher activity of β-NiOOH is attributed to an unidentified Ni oxide formed at a potential above 0.52 V (vs Hg/HgO reference). We have also observed that a submonolayer of Ni oxide deposited on Au exhibits a turnover frequency (TOF) for oxygen evolution that is an order of magnitude higher than that for a freshly prepared γ-NiOOH surface and more than 2-fold higher than that for a β-NiOOH surface. By contrast, a similar film deposited on Pd exhibits a TOF that is similar to that of bulk γ-NiOOH. It is proposed that the high activity of submonolayer deposits of Ni oxide on Au is due to charge transfer from the oxide to the highly electronegative Au, leading to the possible formation of a mixed Ni/Au surface oxide. © 2012 American Chemical Society