Performance of natural dye sensitized solar cells for low power applications

Abstract

The need for renewable energy sources in Sri Lanka is assessed and solar photovoltaics (PVs) is identified to be the most technically suitable and economically viable power source for the conversion of solar energy to electricity in future. Three generations of solar PVs comprising 1st, 2nd and 3rd generations are dentified, and Dye – Sensitized Solar Cells (DSSCs) comprising the 3rd generation cutting – edge solar cell technology is identified being the low-cost easy to manufacture, durable, stable, long life time with reasonably high solar energy to power conversion efficiency (11% max with expensive , scarce, synthetic dyes like Ruthenium bipiridyl complex technology ), or of about 1% with cheap, low-cost, abundant, non-toxic, environmentally friendly natural dyes of photosynthetic green plants. Natural dyes were selected to carry out further research and development work for practical applications. Research done on DSSC’s since inception in Sri Lanka were scrutinized and assessed at the Institute of Fundamental Studies (IFS), Hantana, Sri Lanka, and other Institutions in Sri Lanka. It has been observed that most of the research at the IFS has been done using very expensive synthetic Ruthenium metallic dyes and have achieved a high conversion efficiency of 10% in May 2001. DSSCs sensitized with 145 natural dyes of plants growing in Sri Lanka were electrically and electronically tested and the ethanolic dye extracts of natural Mangoostein fruit rind (deep purple colour) exhibited the best conversion efficiency (of about 1%.) . It was also observed that other natural dyes such as Ekkiriya wood, Egg plant fruit peel, Karawalla kabilla fruit, Banana flower inflorescence, Beetroot tuber, Turmeric root and Fire fern leaf (not endemic to Sri Lanka) yield relatively good conversion efficiencies. Natural dye-based DSSCs even though possess conversion efficiencies usually below 1%, may be improved by finding different additives. Such DSSCs are cost effective , easy to manufacture, environmentally friendly and stable . They are potential solar energy to electricity conversion devices for low power applications if further research is done to boost their conversion efficiencies to about 2% - 3%, and to increase their long term stability. The reasons why DSSC’s have not been developed for commercial use in Sri Lanka have been identified, assessed and remedial measures proposed. Research and development work were also initiated to develop practical DSSCs sensitized with low-cost abundant and environmentally friendly natural dyes of plants for low power applications such as battery charging of mobile telephones, iPod’s, portable radio communications equipment, LED operated multi – coloured garden - night lights of hotels etc., construction of Building Integrated Photovoltaic (BIPV) systems to provide diffused lighting with multicoloured LED operated lighting systems, provision of propulsion power to small boats etc, in order to assist solve the impending energy crisis when all known sources of fossil fuel will be exhausted in a few decades.