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Ultrafast Spectroscopies for Dye Sensitised Solar Cell study and Optimisation

Final Report Summary - ULTRADSSC (Ultrafast spectroscopies for dye sensitised solar cell study and optimisation)

The project was developed at the University of Rome 'Tor Vergata'. The work was planned to be developed in a period of 36 months but the researcher involved resigned for personal reason on 1 May 2009, consequently it was necessary to ask for an early termination of the project. The first year of the work plan has been respected and the planned goals achieved. The first seven months the researcher has familiarised with the instruments of the host institution for the fabrication and the first phenomenological electro-optical characterisation of new DSSCs. The DSS cell has been prepared in different steps:
1) deposition of TiO2 on ITO and particle sinterisation,
2) dye adsorption,
3) making the counter electrode,
4) assemble the two electrodes (25-50 µm distance),
5) filling with electrolyte and
6) sealing the solar cell.

Many experimental techniques could be performed in this first period i.e. the deposition techniques of TiOB2B have been performed using different techniques like squeegeeing, spin-coating and blade coating; the electro-optical properties have been investigated for different annealing temperature and/or different types of dyes. This fabrication steps, especially the preparation of TiO2 film, play a fundamental role in the way charge transport mechanism take place, such as for instance diffusion by percolation in the TiO2 film.

Different materials (other than platinum compounds) have been tested in order to optimize the counter electrode. The structural and textural properties of the films were characterised via Atomic Force Microscopy (AFM) imaging of the top surface of the TiO2 film. The films have a rough surface with average roughness in the µm range. The second step has been the electro-optical characterisation with a sun simulator in order to define the device electrical characteristics and the behaviour under day long solar exposition. In particular, it has been studied the angular dependence of the photocurrent. We made use of a refractive element on the topside and we quantified the strong dependence of photocurrent on the angle of incidence of light in a dye solar cell (DSC). Under laser illumination the photocurrent increases for large incidence angles. The observed enhancements up to 25 % can be useful for evaluating novel designs of an efficient photon management in DSCs.

Starting from the eight month, the ultra-fast time resolved spectroscopy laboratory has been implemented: in this period, after a first valuation of the different solutions proposed by the laser sources and analysing devices markets, the ultra-fast time resolved spectroscopy laboratory has been improved buying the items necessary to perform the different experiments. In order to obtain the best temporal resolution a pump and probe set-up must be used with an appropriate fs laser source. The goal for this part of the project has been accomplished buying a tuneable ultrafast Ti:Sapphire oscillator (Tsunami series) with a pulse duration of ~80 fs pumped by all-solid state pump laser (Millennia® series). The detection part of the set-up has been realised by means of Acton series imaging spectrometer implemented coupled to PIXIS thermoelectric cooled CCD camera platform.

The time resolved set-up includes a high speed and low vibration mechanical delay line suitable for femtosecond experiments).The goal of the whole experiment was the study of electron transfer from the excited electronic state of dye molecules adsorbed on the surface of a solid functioning as electrode. This process has considerable practical and theoretical importance for the efficiency of the DSS cells. Actually, this goal couldn't be achieved due to the early termination of the project.