It might sound like something out of a sci-fi movie, but leveraging fruit dye extracts for use in solar cells is possible in the real world. For the past few years, natural extracts from produce such as jamun, pomegranate, spinach, beetroot, hibiscus, green algae and black carrot have been utilised as solar cell dye and found favour for both scalable and sustainable benefits.
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Popularly known as senduri , rohini or rori among Jharkhand tribal communities, the red kamala tree is a semi-evergreen woody spurge plant that bears fruit only in spring. When Prof. Basudev Pradhan, Assistant Professor at Central University of Jharkhand’s (CUJ) Department of Energy Engineering, looked at the dozens of kamala ( Mallotus phillipensis ) trees across the campus, he decided to investigate the efficacy of this fruit’s extract in creating a non-toxic sensitiser for Dye-Sensitised Solar Cells (DSSCs). And he was proven right.
Earlier this spring, the team comprising researchers Arup Mahapatra, Prashant Kumar, Jyoti Bhansare, Madhavi Surapaneni and Anik Sen, headed by Pradhan, extracted natural dye from the pericarp of the kamala fruit. The extracted dye was used to make an inexpensive, non-toxic sensitiser for DSSCs or Grätzel cells, which directly convert solar energy into electricity. In more molecular context, the presence of carbonyl and hydroxyl groups gets easily anchored to the titanium dioxide nanoparticles (crucial parameters for the power conversion efficiency of dye-sensitised solar cells), which are used to make the photoanode (the component supporting dye molecules and transferring electrons) – an important component of DSSCs.
“We had been conducting solar research for a long time, so we had everything set up in our labs already,” says Pradhan over the phone from Kolkata, “It took us five to six months to complete our work of research, development and testing. We used raw dye which has a lot of impurities, hence we need to purify it to enhance the efficacy.”
This is the first time this dye has been used for solar cell application, he shares. In tandem with the experiment, his team of researchers have also performed theoretical calculations using rottlerin, one of the major constituents of the natural dye, to check the properties and applicability of the proposed dye as a photo-sensitiser and has manifested high electron injection efficiency – an important requirement for efficient solar cells.
‘The best alternative’
How scalable is a solar cell solution like this? “The process itself is low-cost so there is a lot of potential here,” he explains, adding, “The challenge in this process is waiting for the fruit to ripen to reach that pigment of red, which is necessary for a DSSC to work. That said, this kind of non-toxic and biodegradable natural dye can be easily extracted from an inedible source, like the kamala fruit in its untreated form, using a very low-cost technique and therefore it can provide the best alternative to that of toxic and expensive synthetic dye used for solar cells.”
Their work so far has been published as a short communication titled ‘Development of dye-sensitised solar cell using M. philippensis (kamala tree) fruit extract: A combined experimental and theoretical study’ (August 10, 2021) in the International Journal of Energy Research.
The study states the device efficiency is about 0.55% which is quite comparable with other reported devices with natural dye, whereas the efficacy of natural dyes varies from 0.1% to 2%.
Pradhan adds, “As per my knowledge, maximum efficiency so far people reported about 2% from pomegranate fruit juice. Here, we want to emphasise that our dye is extracted from an inedible source. definitely it needs further purification to get better performance. In the case of synthetic dye, the maximum is from the most popular Ruthenium complex (N719) with 11.9% efficiency and 13% using organic dye.”
He points out the dyes are “very stable but when it comes to the device, all the DSSCs with synthetic or natural dye face long term stability challenges because they use liquid electrolyte.” He adds that he and his team are working on that in that aspect as well, and that many research groups are trying to use solid state or gel electrolyte for this purpose.
Naturally, the CUJ team is excited about the potential of food sources as an alternative candidate in developing cost-effective solar cell devices to address the future energy challenge. But the team acknowledges there is still a lot to be done to finalise the true efficacy of the kamala fruit dye extract.
But there is also a design plus to using the kamala fruit dye extract, says Pradhan. “Because of the rich red colour, it looks stunning on the solar cell. We are used to seeing blue, but the red stands out.”