The efficiency of solar cells is like a jigsaw puzzle. All the pieces are disparate. Though the solution depends on every single piece available, the progress depends on some key pieces. The structure and arrangement of the nanoparticles is one such key piece in the puzzle that can lead us to quicker solutions.
Rakesh Sonker, from the University of Delhi, and his colleagues from the Jamia Millia Islamia, Delhi, and the Babasaheb Bhimrao Ambedkar University, Lucknow, wanted to improve the architectural arrangements of molecules in dye-sensitized solar cells. In dye-sensitized solar cells, oxide molecules carry the photons captured from the anode to the cathode. So they tinkered with the surface morphology of zinc oxide molecules.
They grew the nano-needles by controlled precipitation, a commonly used industrial process which allows controlled release of molecules. Systematic delivery leads to a homogeneous, but porous layer of zinc oxide nanoparticles which acts like a network.
The porous network structure increases available surface area, which, in turn, improves the absorption of photons. The nano-needle array functions as an efficient light trap in which sunlight makes several turns and travels horizontally for distances much longer than the array thickness. A linear arrangement provides a direct pathway for rapid transport of the photo electrons. Organic dye sensitised cells, made of these needles, show an efficiency of 4.2%, which, though not high, provides a viable commercial option, due to low costs of production.
“It is easy to print these organic photovoltaics. Simple roll-to-roll printing is sufficient to make these cells”, says Rakesh Sonker, University of Delhi.
The films are quite thin. The nanoneedles are less than 450 nanometers in length – ten thousandth of a millimeter”, adds Rahul from Jamia Millia Islamia.
“The nano-needle design reduces the weight of solar cells and it makes the films flexible. So this fabrication method promises a number of applications” says S R Sabhajeet, Babasaheb Bhimrao Ambedkar University, Lucknow.
The higher flexibility, lower weight and costs of production as well as efficient light absorption enhance the potential uses of the nano-needle solar cells.
Materials Letters: 223;133-136
Manish Kumar Tekam