Dye-sensitized solar cells (DSSCs) have been intensely researched for more than two decades. Electrolyte formulations are one of the bottlenecks to their successful commercialization, since these result in trade-offs between the photovoltaic performance and long-term performance stability. The corrosive nature of the redox shuttles in the electrolytes is an additional limitation for industrial-scale production of DSSCs, especially with low cost metallic electrodes. Numerous electrolyte formulations have been developed and tested in various DSSC configurations to address the aforementioned challenges. Here, we comprehensively review the progress on the development and application of electrolytes for DSSCs. We particularly focus on the improvements that have been made in different types of electrolytes, which result in enhanced photovoltaic performance and long-term device stability of DSSCs. Several recently introduced electrolyte materials are reviewed, and the role of electrolytes in different DSSC device designs is critically assessed. To sum up, we provide an overview of recent trends in research on electrolytes for DSSCs and highlight the advantages and limitations of recently reported novel electrolyte compositions for producing low-cost and industrially scalable solar cell technology.

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The long-term stability of a dye-sensitized solar cell (DSSC) is a key issue for upscaling and commercialization of this technology. It is well-known that gel electrolytes can improve the long-term stability and allow easy DSSC manufacturing. However, there is limited knowledge on the long-term stability of cobalt-based gel electrolytes and also how this stability is affected when applying different dye sensitizers. Moreover, long-term stability studies have been done with no, or an imperfect, sealing. In this work we investigated the performance and the stability of cobalt-based polymer gel electrolytes using devices properly sealed. Here, two different dyes, an organic and a ruthenium dye, were selected to investigate the device's performance. The cobalt liquid electrolyte was gelled with a PEO-based terpolymer (PEO-EM-AGE) and compared to its liquid counterpart. After 1000 h, the efficiencies of the liquid-and gel-based solar cells with the ruthenium dye were statistically similar to each other. On the other hand, the DSSCs using the organic dye performed similarly by statistical analysis only up to 500 h. Our findings suggest that the choice of the dye has an important impact on the long-term stability of DSSCs and must be considered a key factor in the degradation mechanism.

Here we report printed single-walled carbon nanotubes (SWCNT) as a promising catalyst material for copper redox shuttles based electrolyte in dye-sensitized solar cells (DSSC). The SWCNT layers, which were printed at low temperature could serve as an alternative catalyst material since they outperformed the traditional thermally platinized CEs by exhibiting very low charge transfer resistance (∼2.1-2.9 Ω cm 2 ) in both complete DSSCs as well as in a symmetrical CE-CE cells. The superior catalytic activity of printed SWCNT-CEs contributed to better photovoltaic performance and resulted in a higher solar-to-electrical conversion efficiency (7.0%±0.4%) than traditional Pt-CE based DSSCs (6.2% ±0.4%) in full sunlight conditions. The devices fabricated with printed SWCNTs catalyst counter electrodes also exhibited impressive open circuit voltage that almost approached 1 Volt. The champion DSSC with SWCNT CE gave a 7.5% conversion efficiency under full sun illumination and 8.3% under half sun illumination. These two efficiency values are the highest ever-reported efficiencies for SWCNT-based CEs combined with a Cu-based electrolyte in DSSCs. These results could provide a pathway for efficient DSSC-based devices, which can be integrated in futuristic consumer applications for efficiently working under both full sun light and low light intensities.

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One of the major drawbacks in dye-sensitized solar cells (DSSC) is related to the use of a liquid electrolyte, which limits durability and stability. Part of this problem can be solved by replacing the liquid electrolyte by a polymer or gel electrolyte, although the open circuit potential (V OC) of the solar cells is affected. In this work, the role of the reduced graphene oxide (RGO) added to a gel electrolyte in order to improve the efficiency of DSSCs is discussed in detail. The gel polymer electrolyte is composed of poly­(ethylene oxide) (PEO), γ-butyrolactone (GBL), LiI, I2, and different concentrations of RGO. The best solar cell using 0.5 wt % of RGO delivered an efficiency of 5.07 ± 0.97%, with the highest values of I sc and V OC. RGO sheets are acting as a multipurpose component in the electrolyte. The recovery of the V OC values can be related to the removal of polyiodide species from the photoanode surface by interaction with the RGO sheets. The increase in the I sc is assigned to the enhancement in the diffusion of I3 – species and by the reduction of the electron transfer resistance in the counter electrode.

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