Broad absorption natural dye (Mondo-Grass berry) for dye sensitized solar cell

Two major drawbacks in dye-sensitized solar cells (DSSC) are the narrow spectral response and the short-term stability. Research on development of artificial dyes for a broad frequency response is a major field of research today. The work presented here shows a broad response with a natural dye extracted from a Mondo-grass (Ophiopogon japonicus) berry. Its range of sensitivity covers the entire visible region and its tail expands to the near infrared. This is a unique situation since many natural dyes containing anthocyanin or carotenoids strongly absorbed only below 600 nm. A TiO₂ based electrode sensitized with Mondo grass berry dye DSSC was tested for its performance. An open circuit photovoltage of 495 mV and a short circuit photocurrent of 0.6 mA/cm² were obtained under 1 sun illumination. The broad spectral response from 400 to 750 nm was observed for the Mondo-grass berry dye. A high fill factor of 71% was achieved but energy conversion efficiency was only 0.2% for the cell. Even though cell efficiency is low with this dye, the solar cells have exhibited better stability when compared with that of the Blackberry. The thin layer chromatography results indicate that Mondo-grass berry dye contains a mixture of two or more chemical compounds belonging to both the anthocyanin and the carotenoid families.