Carbon is a flexible substrate that provides lightness, conductivity and flexibility to solar cells. This can reduce Ag's optical properties and affect its deposition. In order to avoid this problem, it is common for a diffusion barrier of carbon between the graphite sub-strate and the back reflective layer. This layer can either be made of tin or silicon oxide.
They investigated, therefore, the impact of carbon diffusion barriers on the structure and performances of a counter electrode made of graphite for dye sensitized solar cell. For this purpose, three samples were fabricated with various types of rear reflectors. These included one sample with just the standard back reflective film, another with an Ag-coated graphite substrate, and yet another with SiO2 and SnOx diffusion barriers between the back reflecting sheet and graphite, and finally, a third without a back reflector. These diffraction X rays were used to evaluate the chemical stability and reflectivity of Ag films. A digital oscilloscope was also used to record time-resolved, transient photocurrents spectra measured by a picosecond Pulse Laser. Electrochemical impedance spectroscopy was performed with an IM6ex electrochemical work station in the frequency range of 1 to 1 x 106 Hz under 0.8 V bias.
The use of a CO2 barrier between a graphite counter-electrode and a back reflector in DSSCs improves its performance significantly. This improved performance is due to the uniformity of its surface, the excellent microscopic interaction with the hole-transporting layers and perovskite as well as the simple procedure for preparation. These results show that the carbon diffusion barrier electrode is suitable for low-cost and flexible DSSCs. Discussion is given on its possible applications. Its authors suggest that it could be used in PSCs with other conductive Graphite Materials.
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