Solar cell for indoor use replaces batteries
Epishine in Sweden has launched its organic solar cell technology for indoor use after a decade of development.
The cell is aimed at powering sensors and actuators, including electronic locks, from indoor LED and fluorescent light
“This is a historic day for Epishine,” said Anna Björklou, CEO of Epishine. “ It has taken over 25 years of research and we have developed a production process scalable to large volume. It has been optimised for indoor use, which is why we call it a Light cell rathe thana solar cell.”
The first production version of the solar cell uses a non-fullerene polymer that gives a conversion efficiency of 15 percent with an output of 0.5V and is tuned to indoor light at 400 to 700nm at 20 to 1000lux. The company is working on a version with higher efficiency of 26 per cent using a fullerene material, says Jonas Bergqvist, CTO.
The key is a lamination technology for building the thin cells with recycled plastic materials. “We have developed a method to use lamination instead of sequential printing. We print on two halves and use temperature and pressure to bond the two layers,” said Bergquist. “What is critical for large scale deployment is a high up time so it is important to handle the lower corner cases, down to 50lux. This is especially true in the home environment.”
The cell is aimed for indoor use as the currents generated in outdoor conditions would be too high for the electrodes, he said.
Next: battery-free wireless sensor card
One early customer, Miromico in Switzerland, is using the cell to power a battery-free sensor card.
“MiroCard smartcard powered by light with our electronics on the bottom with sensors and a Bluetooth radio to communicate with infrastructure,” said Andres Gomez, Research Engineer at Micromico. “We will start field trails in mid February and Epishine is a key component as it is thin and flexible that enables a form factor smaller than a credit card. It only takes a few seconds for the device to switch on and start communicating even though it has no batteries.”
It has also been used to replace the batteries in an electronic lock developed by ACSS. The indoor solar cell is used in the lock panel, while the power management and converter fits into the battery compartment that is no longer used.
The cell comes in a 50 x 50 mm square, although larger versions are possible, up to 25cm x 7cm, says Bergquist. This is a restriction of the current manufacturing equipment.
The cell also has restrictions on the manufacturing process. It cannot be used in a reflow PCB process as the high temperatures would damage the plastics and the collection material and so has to be hand soldered into place.
The aim is to go ito mass production with the technology, says Björklou. “We don’t have plans to license the technology but that’s an interesting question. We also want more players in the market with this technology so it’s under discussion,” she said.
Epishine purchased roll to roll manufacturing services from Ynvisible Production (formerly Consensum Production), also based in Linköping, that developes flexible display technology.
The evaluation kit for the cell uses a power management chip from e-peas in Belgium and a supercapacitor from CAP-XX.
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