inkjet printer

Solar cells printed with inkjet onto various surfaces

Image credit: DT

Scientists from King Abdullah University of Science & Technology have printed ultrathin solar cells onto glass and a flexible substrate using an inkjet printer.

Solar cells can now be made so thin, light and flexible that they can rest atop a soap bubble. Along with other novel power devices such as Tengs, solar cells offer an alternative means of powering electronics, such as thin medical patches, for which conventional energy sources would be unsuitable.

“The tremendous developments in electronic skin for robots, sensors for flying devices and biosensors to detect illness are all limited in terms of energy sources,” said Eloïse Bihar, the postdoctoral researcher who led the study at King Adbullah University.

“Rather than bulky batteries or a connection to an electrical grid, we thought of using lightweight, ultrathin organic solar cells to harvest energy from light, whether indoors or outdoors.”

Until now, ultrathin organic solar cells have been manufactured via spin-coating or thermal evaporation; techniques which are not scalable and which limit device geometry. This involves using a transparent and conductive (yet brittle and inflexible) material called indium tin oxide as an electrode.

To overcome these limitations, Bihar and her colleagues applied inkjet printing, formulating functional inks for every layer of the solar cell structure. Rather than using indium tin oxide, they printed with a transparent, flexible, conductive polymer known as PEDOT:PSS.

“Inkjet printing is a science on its own,” said PhD student Daniel Corzo, who worked on the project. “The intermolecular forces within the cartridge and the ink need to be overcome to eject very fine droplets from the very small nozzle. Solvents also play an important role once the ink is deposited because the drying behaviour affects the film quality.”

The printed cell is made up of electrode layers sandwiching a light-capturing organic photovoltaic material. The entire structure can be sealed within a parylene: a flexible, waterproof, biocompatible protective coating. This may render the cell suitable for incorporation into wearable devices.

Solar cell on the surface of a bubble

Solar cell on the surface of a bubble/KAUST

Image credit: KAUST 2020

After optimising ink composition for each layer of the device, the solar cells were printed onto glass to test their performance. The cells reached a power conversion efficiency of 4.73 per cent, surpassing the previous record of 4.1 per cent for a fully printed cell. Bihar’s team also demonstrated for the first time that it is possible to print a solar cell onto an ultrathin flexible substrate, reaching an efficiency of 3.6 per cent.

“Our findings mark a stepping-stone for a new generation of versatile, ultralightweight printed solar cells that can be used as a power source or be integrated into skin-based or implantable medical devices,” said Bihar.

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