S. Galliano

Approaching truly sustainable solar cells by the use of water and cellulose derivatives

Aqueous dye-sensitized solar cells (DSSCs) are emerging as the first truly safe, cheap and eco-friendly photovoltaic technology, at the same time overcoming the well-known instability upon moisture/water contamination typical of many solar cells. While many aqueous DSSCs recently proposed still contain little amounts of organic solvents or petroleum-derived polymeric matrices, here we propose the first 100% hydrogel electrolyte, consisting of carboxymethylcellulose as a green jellifying agent, water and iodide/triiodide redox mediator. Electrochemical and photoelectrochemical properties of the resulting electrolytes and solar cells are thoroughly investigated, with a special focus on the long-term stability of the aqueous devices under different operating and aging conditions. The obtained promising efficiencies and stabilities, combined with a metal-free sensitizer, lead here to sustainable, stable, transparent and building-integrable solar cells, without suffering from any safety and/or toxicity issues.

Panchromatic symmetrical squaraines: a step forward in the molecular engineering of low cost blue-greenish sensitizers for dye-sensitized solar cells.

Two novel symmetrical blue squaraine sensitizers were synthesized, which exhibit panchromatic light harvesting and a record efficiency over 6% with Jsc exceeding 14 mA cm(-2), and Voc over 620 mV under 1 sun. Their color, low cost, easiness of synthesis, and relatively high photo- and thermal stability open up the way for commercial applications.

Near-infrared emitting single squaraine dye aggregates with large Stokes shifts

The study of supramolecular interactions and aggregation behaviour of functional materials is of great importance to tune and extend their spectral sensitivity and, hence, improve the optoelectronic response of related devices. In this study, we resolve spatially and spectrally the absorption and emission features of squaraine aggregates by means of confocal microscopy and absorption/photoluminescence spectroscopy. We observe that the aggregate affords both a broad absorption spectrum (centred at 1.85 eV and extending to 1.55 eV), likely originated by a dye configuration with allowed J- and H-arrangements, and a strong and relatively narrow emission in the near-infrared (NIR) part of the spectrum (centred at 1.59 eV), with a remarkable Stokes shift of 0.26 eV that is among the largest exhibited by squaraine dyes. These peculiarities would be beneficial for extending the spectral sensitivity of photovoltaic/light-emitting diodes and electrochemical cells, and extremely appealing for possible applications of these aggregates as NIR fluorescent probes in biomedical applications.

Spectroscopic investigation of squaraine dyes

We report a study on the excited state dynamics of two symmetric squaraine dyes, carrying different side-groups attached to the squaric ring. By means of UV-VIS absorption and time-resolved fluorescence spectroscopies, we found that the photodynamic of these functional molecules depends strongly on both the steric and electro-donating properties of the side-group.

Excited state photophysics of squaraine dyes for photovoltaic applications: an alternative deactivation scenario

Squaraine dyes (SQs) represent a versatile class of functional molecules with strong absorption and emission features, widely used as near-infrared sensitizers in organic and hybrid photovoltaic devices. In this context, the photodynamics of such molecules has been seen to influence dramatically the efficiency of the photogeneration process. The most accepted interpretation of excited state deactivation in SQs is represented by a trans–cis photoisomerization around a CC double bond of the polymethinic-like bridge, although such scenario does not explain satisfyingly the decay route of SQs dyes in conformational constrained systems or in highly viscous environments. Here we combine steady-state and time-resolved spectroscopic techniques with high level ab initio calculations to shed light into the photophysics of cis-locked indolenine-based SQs. Our results point towards alternative deactivation routes, possibly involving a dark state in molecules lacking central substitution and the rotation of the central substituent in the core-functionalized ones. This study reveals, for the first time, the possible presence of dark electronic states in SQs, a scenario that can be further investigated in molecules exhibiting higher emission yields than cis-locked indolenine-based SQs. Furthermore, these novel results can suggest a synthetic rationale to design dyes that permit quantitative and effective charge generation/diffusion and collection in photovoltaic diodes and, thus, enhance their efficiency.

Correction: Near-infrared emitting single squaraine dye aggregates with large Stokes shifts

Correction for ‘Near-infrared emitting single squaraine dye aggregates with large Stokes shifts’ by G. M. Paterno et al., J. Mater. Chem. C, 2017, 5, 7732–7738.