![]() ![]() The electrodes were then sintered at 500 ☌ for 60 min, followed by a post-treatment process with 40 mM TiCl 4 aqueous solution at 70 ☌ for 30 min. ![]() A 6 μm mesoporous layer of TiO 2 was then printed on the glass by the doctor-blading method from a titania paste (TiO 2 Dyesol 30NR-D), followed by a 6 μm Dyesol WER2-O TiO 2 paste scattering layer. This was followed by a pre-treatment process with 40 mM TiCl 4 aqueous solution at 70 ☌ for 1 h. (48) A solution of 0.2 M titanium di-isopropoxide bis(acetylacetonate) in 2-propanol was sprayed in very short pulses of 1 s duration onto a clean fluorine-doped conductive glass Tec15 placed on a hotplate at 450 ☌. Compact TiO 2 blocking layers were deposited by spray pyrolysis using a hand-held atomizer, following the method developed by Kavan and Grätzel. ![]() DSCs were fabricated using standard procedures. Eventually, such a research direction would result in commercializing non-toxic and eco-friendly DSCs to power indoor devices such as low-power IoTs. (31) Therefore, it becomes intuitive to investigate new aqueous redox electrolytes and their use in DSCs under ambient light conditions. (29,30) Boschloo and co-workers reported an efficiency of 4.3% in LEG4-sensitized TiO 2 and a water-soluble TEMPO redox couple. In addition to the iodide-based aqueous electrolyte systems, other aqueous redox systems have been investigated by different groups such as the thiolate/disulfide redox mediator, (18,25) Fe(CN) 6 4–/3–, (24) and cobalt(II)/(III) tris(2,2′-bipyridine) redox couple. (35) Moreover, reports describing the enhancement of the long-term stability of such DSCs with the use of hydrogels such as xanthan gum (36,40) and lignin (41) have also been shown. reported a 7% efficient iodide-based aqueous DSC when using a cationic PEDOT counter electrode. DSCs with an aqueous iodide-based redox mediator achieved efficiencies between η = 2.4 and 6.0%, (37−39) while most recently, Bella et al. (18−36) Indeed, the most recent reports about this subject have been researching efficiency enhancement and long-term stability of iodide-based aqueous DSCs. This led our group and other researchers to investigate water-based electrolyte systems in DSCs, which in turn minimizes cost, reduces volatility and flammability, and improves their environmental compatibility. However, conventional DSCs contain organic solvent-based electrolytes, which have low boiling points and harmful environmental effects. (5) Such findings render the use of DSCs to power indoor and low-power electronics very attractive. reported a record PCE % of 34.5% under ambient light for a co-sensitized solar cell with a Cu (I)/(II) electrolyte system, attaining a high photo-voltage of 0.98 V at 1000 lux irradiation. Recently, research in the DSC field has been focused on its indoor use under low-light conditions (14−16) and taking advantage of its aesthetic properties. reported one of the highest PCE % (14.3%) that has been obtained with a Co (II)/(III) electrolyte system and V OC values around 1 V, (2) while the highest V OC value of 1.24 V has been attained with a Cu (I)/(II) electrolyte system in acetonitrile by Grätzel et al. (9−12) The ease of ligand modification of these complexes makes it possible to control their redox potentials, electron transfer kinetics, and stability, in addition to the tuning of their chemical and physical properties. ![]() (8) Two of the best one-electron redox couples that have been demonstrated to outperform the I –/I 3 – redox couple, especially when coupled with organic-based dyes, are based on cobalt and copper polypyridyl complexes. (7) Another drawback of this redox mediator is its corrosiveness when it comes in contact with several metals (especially silver that is used as contact leads), affecting its long-term durability. (6) Furthermore, the reduction of I 3 – to I – at the cathode is a two-electron process that causes large internal losses in the cell and high over-potentials that result in lower photo-voltages ( V OC). First, the I –/I 3 – redox couple absorbs light in the visible region, specifically the blue part of the electromagnetic spectrum, and thus lessens the light-harvesting efficiency of the dye-sensitized photo-anode. Despite its remarkable performance in DSCs, scientists have been searching for suitable alternatives due to several reasons. For a long time, the iodide/triiodide (I –/I 3 –) redox couple has been the conventional electrolyte system for use in DSCs, due to the high efficiencies attained with different types of dye sensitizers especially with the ruthenium-based ones. ![]()
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