The performance of a flexible and glass dye-sensitized solar cell (DSSC) with water-based electrolyte solutions is described. High concentrations of alkylamidazoliums were used to overcome the deleterious effect of water and, based on this variable, pure water-based electrolyte DSSCs were tested displaying the highest recorded efficiency so far of 3.45% and 6% for flexible and glass cells, respectively, under a simulated air mass 1.5 solar spectrum illumination at 100？mWcm？2. An improvement in the with high water content and the positive impact of GuSCN on the enhancement of the performance of pure water-based electrolytes were also observed. 1. Introduction Dye-sensitized solar cells (DSSCs) are considered so far to be the best low cost alternative to silicon photovoltaic cells [1–3] demonstrating an efficiency of up to 12% [4] and have been intensively studied since their discovery in 1991 [5]. The underlying process for this technology relies upon a sensitizing dye adsorbed onto the surface of a very thin, porous, ceramic-like sponge made of titanium dioxide (TiO2), a commonly available material. The dye traps light and then uses this energy to inject an electron into the TiO2. These electrons become available for producing useful electricity when the TiO2 is connected through an external load, such as a battery, light, or other electrical devices, thus closing the circuit so that the electrons are returned back to the dye. The flexible DSSC modules are made of thin and flexible polymers or foils, which are tough, durable, safe to use, and environmentally friendly since the electricity produced is clean and the manufacturing processes are based on abundant, recyclable materials. However, water can permeate into the device relatively rapidly due to the flexible plastic design as opposed to glass. Permeation can be reduced by barrier layers, but this increases the cost. Water was frequently used as an electrolyte in early DSSCs but was abandoned in favour of organic solvents that gave much higher cell efficiencies. In the past, many reports were of the opinion that water was poisonous for DSSCs and that the presence of even a slight trace of water in the electrolyte would be detrimental to the cell performance and would reduce cell stability either by dye detachment [6], by formation of iodate [7], or by a decrease in electron life-time [8]. Recently, however, it has been thought that water-based DSSCs could be relevant to DSSC development since cells, properly optimized to work with water, can give reasonable efficiencies [9] and display other
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