Jamun-based solar cells

The Indian solar segment is on the path to achieving 100 GW of installations by 2022 with tariffs falling to record levels in recent auctions. While declining tariffs result in falling margins, the saving factor is that there is also a significant drop in capital costs and increase in efficiencies. In this context, dye sensitised solar cells (DSSCs) have proven to be an important concept.

These are third-generation solar photovoltaic (PV) cells that generate energy in a process similar to artificial photosynthesis. The dye used in the solar cell is the photoactive material of DSSC, which can produce electricity once it is sensitised by light and uses energy to stimulate electrons, much like chlorophyll in photosynthesis. The dye then injects these electrons into titanium dioxide, which conducts away the electron. A chemical electrolyte in the cell then closes the circuit.

Spearheading India’s research and development in the solar segment, researchers at IIT Roorkee, Dr Nipun Sawhney and Dr Soumitra Satapathi, recently invented a special type of DSSC. They went a step beyond the current technologies used for manufacturing DSSCs by substituting one of the most expensive components of a traditional DSSC, the Ruthenium-based dye, which costs more than $1,000 per gram, with a natural dye extracted from fruits. The researchers used dyes from Jamun, berry juice, black currant pulp and plums. The bottled berry juice and black currant pulp were used directly, while dyes had to be extracted from the jamun and plums. The team then manufactured the DSSC with the fruit extracts and tested black currant and mixed berry dye extracts in simulated conditions of 350 watts per square metre illumination, while jamun and plum dye cells were tested in 960 watts per square metre illumination simulated conditions.

The team found that DSSC comprising black currant and mixed berry dye showed a conversion efficiency of 0.55 per cent and 0.53 per cent respectively, while DSSC comprising jamuns and plums showed a conversion efficiency of 0.235 per cent and 0.261 per cent respectively. While these efficiencies are fairly low, the team mentioned that the reason could be the presence of impurities during the extraction of dyes from jamuns and plums, and the direct use of packaged berry juice and black currant pulp that might contain mitigating preservatives and other chemicals. An industrial setup to extract the dyes and manufacture DSSCs may lead to a much higher efficiency by means of reducing manufacturing defects and streamlining the process.

In spite of the low values of conversion efficiencies, this innovation has the potential to lead to widespread applications of fruit extracted DSSC, owing to low manufacturing cost, abundant  raw material, simplicity of the manufacturing process, and economies of scale achieved due to the wide range of DSSC applicability. The dye extraction process from fruits is expected to be significantly cheaper as compared to Ruthenium-based dye, which can reduce the overall capital costs of solar energy generation.

This innovation is a part of an initial step towards the manufacturing of such DSSCs. Given that DSSC technology was introduced in the late 1980s, it will take some more time before it can be commercialised on a large scale. Although DSSCs are cheaper and easier to manufacture as compared to traditional PV cells, their conversion efficiency is lower than that of traditional PV cells. The peak efficiency achieved by DSSCs in laboratory conditions is about 13 per cent, while 6-7 per cent efficiency is considered excellent. On the contrary, traditional PV cells have achieved a peak efficiency of 44 per cent in laboratory conditions, with a practical industry standard of 20-22 per cent. The low conversion efficiency is compensated to some extent by the ease of manufacturing, better performance under cloudy conditions, higher efficiency in higher temperatures and ease of use in applications such as rooftop solar.

The low value of conversion efficiency implies that so far DSSCs have not been used in utility-scale projects. Since these have not witnessed large-scale adoption, it will take a significant amount of time before fruit extract-based DSSCs are commercialised. However, going forward, fruit-based DSSCs could become a reality with greater research and significantly higher efficiencies that can completely change the Indian solar segment.