A combined experimental and computational study is carried out to understand the nature of the interfaces between dye-sensitized TiO 2 and cobalt-based electrolyte in the presence of a prototype co-absorbent, chenodeoxycholic acid (CDCA), employed in Dye-Sensitized Solar Cells (DSCs). It was recently reported that including CDCA both in the dye and in the electrolyte solutions substantially improved the performance of DSCs based on a Fc/Fc + electrolyte (Daeneke et al. Nat. Chem. 2011, 3,1755). Here we evaluate the individual and combined effect of CDCA as a surface co-adsorbent and as an additive in DSCs based on a Co(II)/Co(III) electrolyte, in combination with two prototypical Ru(II) dyes, N719 and Z907. For both dyes, the concomitant use of CDCA in the dye bath and in the electrolyte solution leads to a significant improvement, by ca. a factor 2, of the DSCs photovoltaic performances, allowing us to reach 5.3% efficiency with Z907. FT-IR analyses conducted on the solid and TiO 2-adsorbed CDCA highlight the presence of surface-adsorbed interacting CDCA molecules, possibly creating a bulky insulating network on the TiO 2 surface. Computational analyses have been carried out to gain insight into the nature of the supramolecular aggregates occurring for CDCA on the TiO 2 surface.

Hybrid devices employing organic semiconductors interfaced with an aqueous solution represent a new frontier in bioelectronics and energy applications. Understanding of the energetics and photoinduced processes occurring at the organic/water interface is fundamental for further progress. Here, we investigate the interfacial electronic structure of poly-3-hexylthiophene (P3HT) sandwiched between an indium tin oxide (ITO) electrode and a liquid water electrolyte. The aqueous solution is found to polarize the polymer outermost layers, which together with the polymer p-(photo) doping by dissolved oxygen localizes photogenerated electrons at the P3HT/water interface, while holes can be transferred to the ITO electrode. Under illumination, the polymer/water interface is negatively charged, attracting positive ions from the electrolyte solution and perturbing the ion distribution in the aqueous solution. The observed mechanism is of general character and could underlie the behavior of a variety of devices characterized by an organic/water interface, such as prosthetic devices for artificial vision and organic-based systems for photoelectrochemical applications.

Two new metal‐free organic dyes, CR29 and CR52, with high extinction coefficients in the visible spectral region between 400–650 nm, have been synthesized. The donor–acceptor structure of the dyes feature benzodithiophene moieties BDT1 and BDT as rigid π‐conjugated spacers, which have so far been very little studied for dye‐sensitized solar cell (DSSC) applications. DFT/TDDFT calculations have been employed to guide the design of the chromophores as well as to shed light on their electronic and optical properties. Photophysical and electrochemical characterization studies have been carried out to gather information on the charge transfer processes occurring at the dye–semiconductor interfaces. Under standard AM 1.5 conditions, DSSC sensitized with CR29 showed good conversion efficiencies: 5.14 % in the liquid electrolyte cell setup and 2.47 % in the solid‐state DSSC.