Electron dynamics dependence on optimum dye loading for an efficient dye-sensitized solar cell

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 217; no. 1; pp. 236 - 241
• Main Authors: Kantonis, G., Stergiopoulos, T., Katsoulidis, A.P., Pomonis, P.J., Falaras, P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2011
• Subjects: Dye loading; Dye-sensitized solar cells; Electron transport; Recombination; Titania annealing; Dye loading; Titania annealing; Recombination; Dye-sensitized solar cells; Electron transport
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2010.10.015

Increasing surface area and optimum dye loading are among the prerequisites for an efficient TiO 2-based dye-sensitized solar cell (DSC), since they improve light harvesting but, at the same time, affect, in a variant way the electron dynamics in the semiconductor. Into this context, in this work, the interdependence of these two effects was investigated. The thermal annealing conditions of nanocrystalline titania films were modified between 400 and 550 °C in order to vary the crystallinity and the aggregation/sintering degree of the semiconductor particles. The annealing effects on the structural and surface parameters of the films were determined and the electron dynamics inside the semiconductor were elucidated. The film properties were found to correlate with the photoelectric conversion efficiencies of the corresponding DSCs in terms of light harvesting efficiency, electron transport, recombination and trapping at surface states. Despite higher dye loading, a relatively low efficiency (5.3%) was attained at the temperature of 400 °C, due to insufficient neck growth and the presence of surface states that were not removed by annealing. On the contrary, the highest efficiency (6.4%) was attained at 550 °C, where high values of electron diffusion coefficients and enhanced electron lifetimes were observed despite a significantly lower dye loading. The above results point out the significance of properly controlling both light harvesting and electron dynamics in the photoelectrode for efficient dye sensitization of a large band gap semiconductor.