Dye‐sensitized solar cells (DSSCs) that use an aqueous (40 % w/w water content) choline chloride based deep eutectic solvent as an electrolyte medium have been investigated. The joint combination of the eutectic mixture and an appropriate hydrophilic sensitizer afforded a DSSC with a power conversion efficiency comparable to that using the same electrolyte composition but with conventional, toxic, and volatile solvents as the medium, which thereby paves the way to a new generation of eco‐friendly, nature‐inspired, low‐cost solar devices.

Photocatalytic reactions could enhance the share of chemicals produced through renewable sources. The efficiency of photocatalysts drastically depends on light absorption, on the surface energy of the crystals, and on the properties of the nanobuilding blocks assembled in devices. Here, we show that photoelectrochemical water oxidation on brookite TiO2 nanorods is greatly enhanced by engineering the location of Au nanoparticles deposition. Brookite photoanodes show a very low onset potential for water oxidation to H2O2 of −0.2 VRHE due to energetics of exposed crystal facets. By combining electrochemical measurements and ultrafast optical spectroscopy, we link the water oxidation activity with electron–hole recombination phenomena. The preferential Au decoration at the electrode/water interface produces highly enhanced photocurrent, while when Au is distributed along the whole film thickness, the activity is depressed with respect to pure brookite. In the latter case, Au nanoparticles act as recombination centers with plasmonic carriers recombining on the same time scale of their generation (fs). Conversely, Au surface decoration enables a hot electrons lifetime 4 orders of magnitude longer (ns) due to efficient hopping on brookite lateral facets, thus providing an efficient path for plasmon-enhanced solar water oxidation

The use of a hydrophobic eutectic solvent based on dl-menthol and a naturally occurring acid such as acetic acid has been tested as an eco-friendly electrolyte medium in dye-sensitized solar cells. In the presence of a de-aggregating agent and a representative hydrophobic organic photosensitizer, the corresponding devices displayed relatively good power conversion efficiencies in very thin active layers. In particular, the higher cell photovoltage detected in comparison to devices based on toxic and volatile organic compounds may stem from a more efficient interface interaction, as suggested by electrochemical impedance spectroscopy studies showing greater charge recombination resistance and electron lifetime.

The photoelectrochemical approach to photoinduced water splitting is gaining increasing interest for solar fuels generation. Dye‐sensitized photoelectrochemical cells (DS‐PEC) have been studied to improve the collection of the Vis range of solar radiation. Metal complexes have so far been the most investigated dyes but in recent years metal‐free organic dyes have emerged as a new frontier for the evolution of the sector. This Minireview systematically describes the use of organic sensitizers and has been organized in terms of dye‐sensitized photoactive electrode(s): photoanode; photocathode; tandem DS‐PEC with photoanode and photocathode. The main classes of dyes are introduced and described in their key properties, device performance, and water splitting data. Thanks to the increasing number of articles, this review highlights the growing importance of organic sensitizers and their molecular design for a more efficient solar generation of clean fuels.