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Luminescent Down Shifting of the Incident Spectrum to Enhance the Performance of Dye-Sensitized Solar Cell

Hosseini, Zahra | 2014

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45995 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Taghavinia , Nima; Mehrany, Khashayar
  7. Abstract:
  8. Luminescence down shifting (LDS) of the incident spectrum is a practical strategy that helps to increase the light harvesting efficiency by manipulating the incident spectrum instead of interfering with the active material inside the cell. In this research, for a dye-sensitized solar cell with a near-infrared sensitizer, the photovoltaic performance was enhanced remarkably with a reflective luminescent down-shifting (R-LDS) layer. Different inorganic phosphors with different luminescent quantum efficiencies have been used as the down shifting materials to increase the light-harvesting efficiency of DSSCs sensitized with TT1 and SQ1 dyes. Four different structures were examined to find the best structure for applying the LDS layer. In two structures, the LDS materials have been placed outside the DSSC and in the other two structures, this layer have been placed inside the DSSC either on the TiO2 layer or on the Pt layer. Best results have been achieved with SQ1/CaAlSiN3:Eu2+ dye/phosphor match. Relative enhancements greater than 200% in IPCE near 500 nm and 40-54% in JSC were achieved, attaining 5.0 and 4.8% overall efficiencies of power conversion for the R-LDS layer coated outside the DSSC, on the counter electrode (front illumination) and working electrode (back illumination), respectively.
    We also did an optical analysis on the loss mechanisms in a reflective LDS (R-LDS)/DSSC configuration. The optical model is first validated using experimental data, and then several possible modification approaches are proposed towards the ideal conditions. Non-unity luminescent quantum efficiency (QE) of the LDS layer and light absorption by the electrolyte inside the DSSC are shown to be the most significant loss channels. Idealization of LDS QE (from 51% to 100%), employing more transparent electrolytes (such as Co complexes) and anti-reflection coatings are three major factors to improve the light harvesting efficiency by ~20%. The possibility of reaching a wider light-harvesting spectral band (up to 800 nm) is studied based on a new dye/LDS couple: a near-infrared absorbing squaraine dye (VG5) and CaS:Yb2+ phosphor. The calculated light harvesting efficiency shows a considerable enhancement in the near infrared region, and the maximal short-circuit current density (Jsc) calculated to be 22.1 mA cm-2 for the device with a R-LDS configuration. The device with a conventional transmissive LDS (T-LDS) configuration has a smaller Jsc value compared to that of the R-LDS counterpart, due to two fundamental loss channels: reflection from the T-LDS surface and the loss from the escape cone.
  9. Keywords:
  10. Dye Sensitized Solar Cells ; Phosphorus ; Titanium Dioxide Nanoparticles ; Light Harvesting Efficiency ; Luminescent Down-Shifting (LDS)Layer ; SQ1 Dye

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