Ultrathin organic solar cells are usually made using spin-coating or thermal evaporation. Although these are very efficient fabrication methods, they’re not very scalable and often lead to size restraints. These fabrication techniques also require the use of indium tin oxide (ITO), which is very brittle and inflexible.
Now, researchers at King Abdullah University of Science & Technology claim that they’ve printed ultralight, thin, and flexible solar cells using an inkjet method.
The new solar cells could lead to an alternative way to power novel electronic devices, where conventional energy sources such as batteries are incompatible with the device’s design. This could apply to medical wearables like skin patches or in sensing technologies like biosensors.
To overcome the limitations presented by ITO electrodes, the research team turned to inkjet printing. According to Daniel Corzo, a Ph.D. student working on the project, the study was successful due to the specially-formulated inks used for each layer of the solar cell’s architecture. Developing these inks was particularly challenging, he added.
A key challenge for the research team was to develop a functional ink capable of printing solar cells. Image used courtesy of Anastasia Serin, King Abdullah University of Science & Technology
“Inkjet printing is a science on its own. 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 behavior affects film quality,” Corzo explains.
An Alternative to ITO
The team also had to find an alternative to ITO, which would be an unsuitable electrode for the researchers’ highly flexible solar cell. Instead of using ITO, the team printed a flexible, transparent, and conductive polymer, poly(3,4-ethylene dioxythiophene) polystyrene sulfonate, more commonly known as PEDOT:PSS.
Researchers at King Abdullah University of Science & Technology say that they’ve printed solar cells that are so light, thin, and flexible that they can rest on a bubble. Image used courtesy of Anastasia Serin, King Abdullah University of Science & Technology
The solar cell’s electrode layers sandwiched a light-capturing photovoltaic material and the entire device was sealed within parylene, a flexible and waterproof biocompatible protective coating. Once the ink had been perfected and optimized for each layer of the device, the solar cells were printed onto sheets of glass for performance testing.
A New Standalone Power Source
The research study notes that the solar cells achieved a power conversion efficiency of 4.73 percent, which beats the previous record of 4.1 percent for a fully-printed solar cell. For the first time ever, this study also demonstrates that a solar cell can be printed onto an ultrathin flexible substrate and achieve a notable power conversion efficiency of 3.6 percent.
The researchers are hopeful that their findings could represent a major leap forward for a new generation of ultra-lightweight printed solar cells that can be used as a standalone power source or be integrated into devices, such as skin-based and implantable medical wearables.
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