• Energy Research

Hybrid electrochromic (EC) devices present an interesting configuration in which the advantage of both solid-state and liquid-based devices can be combined in order to optimize the device performances. In this configuration, a solid-state EC material is combined with a redox couple dissolved in the electrolyte. The redox electrolyte offers an unlimited charge capacity, thus allowing to fully exploit the electrochromic properties of the EC material. Here, we present a thiolate/disulphide (T/T) redox couple as a new redox shuttle for EC devices. In order to transfer the advantages of the redox couple to a solid state device, it was combined with a fully transparent thermally curable vinyl-acetate polymer. The obtained EC device was compared with that based on I/I showing higher transparency in the visible region of the solar spectrum and higher coloration efficiency. Most interestingly, the device based on T/T shows a slower self-bleaching process and it only loses 30% of its coloration after 1 h at open circuit. Such characteristic represents a great advantage for smart windows applications since it is not necessary to apply potential to maintain the device coloration, thus allowing a great energy saving.

Three novel 2D-p-A metal-free organic dyes TK 7e9 containing a dibenzofulvene (DBF) linked to two thiophene units as the p-bridge, diarylamines with and without alkoxy chains as donor groups and the cyanoacrylic acid moiety as the acceptor and anchoring group were synthesized. The new dyes TK were characterized by optical and electrochemical measurements and density functional theory calculations and were used as sensitizers in liquid dye-sensitized solar cells. The effects of alkoxy-functionalization of donor moiety and of hexyl chain insertion onto one thienyl ring of p-linker on dye properties and performances were investigated. The results discover the dye TK7, bearing two simple diphenylamine groups without alkoxy chains, exhibits the best behavior in terms of light absorption and cell performance (PCE of 7.9% and photovoltaic parameters of Jsc of 17.82 mA cm2 , Voc of 670 mV and FF of 0.66). Lower power conversion efficiencies of 6.3% and 6.1% were found for TK8 and TK9, respectively, as a consequence of the presence of the alkoxy chains.

Novel triphenylamine (TPA)-based organic dyes were synthesized and assessed for their performance in dye-sensitized solar cells (DSSCs). In the dyes considered the TPA group and the cyanoacetic acid have the role of electron-donor and -acceptor, respectively, whereas a thienyl-fluoro-phenyl-substituted was introduced as ?-linker to improve the dye performance in DSSCs. Experimental characterizations empasize that the presence of electron withdrawing substituents in the linker close to the electron-acceptor moiety leads to a more efficient intramolecular photoinduced charge transfer. In fact, photovoltaic experiments reveal that the DSSCs based on the thienyl-o-fluoro-phenyl substituted dyes yield a better solar-energy-to-electricity conversion efficiency.

A series of push-pull organic dyes based on the cyanoacrylic acid as the acceptor/anchoring group, a dibenzofulvene (DBF) connected with thienyl rings as the ?-bridge, and donor units linked to different positions of the DBF molecule were synthetized and studied. The effects of the donor position on optical and photovoltaic properties were investigated through photophysics, electrochemical and photovoltaic measurements. The results uphold photovoltaic performances largely depend on the electronic structure of the dyes with a synergistic interaction between donor and acceptor groups. In detail, a fine tuning of the photophysical properties can be reached simply selecting the position of the donor unit on the DBF molecule. In particular, the dyes bearing the donor unit on the 3,6-positions of the DBF show better performances in term of light absorption and cell efficiency with respect to the dyes with the donor unit on the 2,7-positions.

We here report the implementation of poly[(3-N-methylimidazoliumpropyl)methylsiloxane-co-dimethylsiloxane]iodides as suitable polymeric hosts for a novel class of in situ cross-linkable iodine/iodide-based gel-electrolytes for dye-sensitized solar cells. The polymers are first partially quaternized and then subjected to a thermal cross-linking which allows the formation of a 3D polymeric network which is accompanied by a dramatic enhancement of the ionic conductivity.