Assessment of Luminescent Downshifting Layers for the Improvement of Light-Harvesting Efficiency in Dye-Sensitized Solar Cells

Abstract

Luminescence downshifting (LDS) of light can be a practical photon management technique to compensate the narrow absorption band of high-extinction-coefficient dyes in dye-sensitized solar cells (DSSCs). Herein, an optical analysis on the loss mechanisms in a reflective LDS (R-LDS)/DSSC configuration is reported. For squaraine dye (550-700 nm absorption band) and CaAlSiN3:Eu2+ LDS material (550-700 nm emission band), the major loss channels are found to be non-unity luminescence quantum efficiency (QE) and electrolyte absorption. By using an ideal LDS layer (QE=100%), a less absorbing electrolyte (Co-based), and antireflection coatings, approximately 20% better light harvesting is obtained. If the absorption/emission band of dye/LDS is shifted to 800 nm, a maximal short-circuit current density (J(sc)) of 22.1 mAcm(-2) can be achieved. By putting the LDS layer in front of the DSSC (transmissive mode), more significant loss channels are observed, and hence a lower overall efficiency than the R-LDS configuration.