Transparent solar cell concept and prototype (via ACSNana & UCLA)
UCLA is increasing the odds of having electrical devices that recharge simply using the sun. Their goals are to keep the cells cheap while allowing for more power conversion efficiency (PCE) and transparency of visible light.
To do this, the team of researchers from UCLA’s Henry Samueli School of Engineering and Applied Science, their department of Chemistry and Biochemistry and the California NanoSystems Institute, is using a transparent, flexible and lightweight polymer solar cell that can be mass produced at low costs. To meet their goal, they are capturing mostly near infrared (NIR) and ultraviolet photons that lie outside the visible spectrum.
Their PV cell is composed of four layers. As the bottom electrode, the team used ITO+PEDOT:PS (iodine titanium oxide + a macromolecular conductive salt). Above this, a UV and NIR photosensitive active material composed of PBDTT-DPP:PCBM (a composite low band gap polymer) is covered by a TiO2 layer. One of the challenges for the UCLA teams was finding a material to use as a cathode that was transparent while also a good enough conductor. A breakthrough came when they found that a composite made out of silver nanowires (AgNW) fit their necessities.
This AgNW layer can be spray-coated using alcohol-bases solvents, which means cheaper manufacture cost. The TiO2 layer is there to enhance the connectivity between the silver nanowires, as well as the conductivity between them and the photosensitive layer underneath.
The results of this experimental phase were polymer PV cells with a PCE of 4% and a maximum 66% transparency of 550 nm light waves. Recent developments in the manufacture of polymer solar cells have obtained PCEs of 10.6% and researchers believe 15% efficiencies are in the near future so there is plenty of room for improvement.
The team is still years away from producing something that can be implemented to devices or consumer products. The low cost will be the selling point once the PCE can be increased. Still, it feels good to know there will be a day when we will not have to worry about running out of juice as long as the sun is shining.