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A simple hemi-squaraine dye (CT1) has been studied as a TiO2 sensitizer for application in dye sensitized solar cells (DSCs) by means of a combined experimental and theoretical investigation. This molecule is a prototype dye presenting an innovative anchoring group: the squaric acid moiety. Ab initio calculations based on Density Functional Theory (DFT) predict that this acid spontaneously deprotonates at the anatase (101) surface forming chemical bonds that are stronger than the ones formed by other linkers (e.g. cathecol and isonicotinic acid). Moreover an analysis of the electronic structure of the hybrid interface reveals the formation of a type II heterostructure ensuring adiabatic electron transfer from the molecule to the oxide. DSCs containing hemi-squaraine dyes were assembled, characterized and their performances compared to state of the art cells. Experimental results (large incident photon-to-electron conversion efficiency and an efficiency of 3.54%) confirmed the theoretical prediction that even a simple hemi-squaraine is an effective sensitizer for TiO2. Our study paves the way to the design of more efficient sensitizers based on a squaric acid linker and specifically engineered to absorb light in a larger part of the visible range.

Spherical hybrid cyanine-silica nanoparticles, quite homogeneous in size (ca. 50 nm) were prepared by the reverse microemulsion method. Solvatochromism tests indicated that all fluorophore molecules were actually entrapped within the inorganic matrix. The combination of steady-state and time-resolved fluorescence measurements allowed us to conclude that almost all cyanine molecules exhibited the same photophysical behavior and this suggested they should be dispersed in a monomeric form. Such behavior resulted in a significant brightness enhancement per cubic nanometer of nanoparticle with respect to molecules in solution. The occurrence of the optical interparticle effect by progressively decreasing the distance among hybrid nanoparticles passing from suspension to a dry powder was also investigated.

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