Titanium dioxide has been used in dye-sensitised solar cells for more than two decades now. But the material responds to light in the ultraviolet range only. Dyes – typically, ruthenium – help extend absorption to the visible range. But such dyes are costly. And their photoconversion efficiency is low.
P. N. Bhosale and team from the Shivaji University, Kolhapur reasoned that tweaking titanium dioxide’s morphology can improve solar cell efficiency. Titanium dioxide nanorods and nanowires transfer electrons easily. Nanoflower morphology increases
surface area for absorbing light and loading dye. However, it is difficult to create nanoflowers of specified shapes. Last fortnight, the team reported overcoming the problem.
They took titanium tetraisopropoxide as precursor for titanium dioxide. And dissolved it to super saturation in an aqueous solution of hydrochloric acid. For the self-assembly
of titanium dioxide crystals, a fluorine-doped tin oxide substrate was provided. The solution was kept at 130 degrees centigrade.
The researchers took out samples at three, five, seven and nine hours to examine the morphology of the crystals. The crystals grew as highly ordered nanostructures. At three
hours, the titanium dioxide deposition resembled a bottlebrush flower. At nine hours of incubation, the nanorods clustered into cauliflowers. The morphology of titanium dioxide deposition was time dependent.
The team used betanin vegetable dye as photosensitizer. Betanin anchors well to titanium dioxide. Photons absorbed by the dye change its electronic configuration and these electrons are also transferred to the titanium dioxide. Thus, the photoconversion
efficiency of the dye-sensitised nano-cauliflowers increased to 14.21%. The efficiency decreased slightly to 12.01% after 5 weeks. However, the cells were still stable.
The team thus showed that it is possible to create titanium dioxide nanoflowers with specified morphologies and, hence, specific properties. Cauliflower-shaped nanostructures harvest solar energy better. Given the low cost of producing
such dye-sensitised solar cells and increasing efficiencies, the technology may not take long to appear on roof tops.
J. Alloys and Compounds, 790: 1001-1013 (2019);
Dr Hari Singh Gaur Central University, Sagar
*This is a revised version of a report written during a workshop on science writing organised by Current Science in NCPOR Goa, and later published in the column, Science Last Fortnight in Current Science.