Hemisquaraine Dye Performance on Different Photoanodes

We have recently proposed a new metal-free organic dye, CT1, based on a simple hemisquaraine molecule. The CT1 dye is prepared following an easy and inexpensive three steps synthesis: quaternarization, coupling and hydrolysis, according to a classical procedure for hemisquaraine dyes. It exhibits a wide visible absorption band and a good average molar extinction coefficient of 15220 M-1cm-1: the first obtained results on TiO2 photoanodes evidenced good electric characteristics of the final device. Moreover theoretical calculations based on Density Functional Theory and Time Dependent DFT showed a large displacement of electron charge towards the anchoring group in the excited state and a strong chemical bonding between the squarate moiety and the semiconducting oxide surface. In this work our aim is to study the behavior of CT1 dye when it is adsorbed on two different nanostructured semiconducting oxide surfaces: traditionally employed nanoparticle-based TiO2 and the sponge-like ZnO with the same layer thickness (8 um). These ZnO films are fabricated in our laboratory by a simple method based on RF magnetron sputtering deposition followed by thermal oxidation and exhibit a high density of branches and a specific surface area of 14.1 m2/g. A photoconversion efficiency value of 6.67% was obtained with an 18 μm thick film impregnated with N719 sensitizer. We have examined different CT1 impregnation times in the range 5 min-6 hours, studying the dye loading and absorption properties of the photoanodes and comparing with the obtainable DSSCs photoelectrical performances as shown in figure. We will discuss the experimental results in terms of the theoretical predictions obtained from ab-initio calculations on CT1/anatase and CT1/ZnO interfaces.