Materials for Energy

The development of new dyes with superior spectroscopic properties is crucial for increasing the efficiency of dye-sensitized solar cells (DSSCs) and luminescent solar concentrator (LSC). In close collaboration with synthetic and theoretical chemists we aim to understand the structure-function relationships enabling to go a step forward into the realization of improved photovoltaic devices.

In DSSCs, solar light is harvested by an organic or metalorganic dye molecule, linked on a nano-crystalline thin-film semiconductor through a molecular bridge. One of the crucial aspect of DSSCs is therefore represented by the light aborption dye, whose most important properties should meet the criteria for high absorption coefficients, long term stability, high yield for interfacial eletron transfer into the semiconductor CB and relatively slow charge recombination. Organic dyes usually present a D(donor)–π(bridge)–A(acceptor) structure which allows for a rational design of the system and the independent optimization of the different block components. By systematically varying the structure of the different components it is possible to monitor the effect of each part of the dye on electron transfer efficiency.

Charge injection in DSSCs

Recently, notable attention has been devoted to the optimization of the acceptor anchoring groups, an essential part of the sensitizer which should ensure a good electronic communication with the semiconductor and a stable binding with the surface. Comparing the spectra in solution and solid state, time resolved spectroscopy allows to identify the dye cation and to study the kinetics of its formation.

Newly synthesized dyes with siloxane anchoring group.

Transient absorption kinetics of siloxane-based dyes in DCM (left) and TiO2 (right). From: Castellucci E., et al, PCCP, 2017, 19, 15310-15323, DOI: 10.1039/C7CP01956D

Dyes based on quinoxaline core absorb light in the 370-550 nm range and present emission maxima at 550-600 nm. They are very promising as luminescent solar concentrators thanks to the excellent quantum yields and remarkable internal and external photon efficiencies they exhibit in PMMA and PCMA matrices.