By Gary Thomas
Research carried out at Northwestern University, Chicago, has yielded a new solar cell that addresses the limitations of current solar cells.
The new device that makes optimum use of nanotechnology is not just economical, environmental friendly and high on operating efficiency, but also eliminates the limitation of the Grätzel cell. The Grätzel cell scores high on all aspects except for one problem that their life is not more than 18 months. This is because the organic liquid used as the cell’s electrolyte has a tendency to leak and corrodes the cell. The Northwestern cell is all solid. It comprises a compound of cesium, tin and iodine, dubbed as CsSnI3, composed into a thin film.
The teams led by Northwestern’s chemist Mercouri Kanatzidis and nanotechnology expert Robert P. H. Chang combined their expertise to develop the new cell. The cell measures 1 sq. cm with a thickness of 10 microns. Nano particles of titanium oxide are used as n-type semiconductor and the CsSnI3 film serves as a soluble p-type semiconductor. The junction is made of nanoparticles coated with sunlight-absorbing dye. The nanoparticles are optimally sized at 20nm diameter to allow the special liquid developed by Kanatzidis team to flow in between. The liquid is similar to paint solvent that solidifies in time. It is at this solid junction that the light photons are converted to electricity.
The Grätzel cell can convert up to 12% of the incident sunlight into electricity. The Northwestern cell is not far behind and is shown to have a conversion efficiency of around 10.2 %. This is the highest efficiency ever reported for a solid-state cell. The next step in the project is to develop a complete array of cells.