Monolithically integrated photo battery achieves high voltage

Scientists from the University of Freiburg’s Cluster of Excellence Living, Adaptive, and Energy-Autonomous Materials Systems (livMatS) have developed a monolithically integrated photo battery that consists of an organic polymer-based battery and a multi-junction organic solar cell. The battery is reportedly the first monolithically integrated photo battery made of organic materials that has achieved a discharge potential of 3.6 volts, and is therefore capable of powering miniature devices.

Networked intelligent devices and sensors can improve the energy efficiency of consumer products and buildings by monitoring their consumption in real time. Miniature devices like these being developed under the concept of the Internet of Things require compact energy sources in order to function autonomously. Monolithically integrated batteries that generate, convert and store energy in a single system could be used for this purpose.

The researchers developed a scalable method for the photo battery, which enabled them to manufacture organic solar cells out of five layers. Robin Wessling from the University of Ulm said the system achieved 4.2 volts with this solar cell. This multi-junction solar cell was combined with a so-called dual-ion battery, which can be charged at high currents, unlike the cathodes of conventional lithium-ion batteries. With careful control of illumination intensity and discharge rates, a photo battery constructed in this way can be charged in less than 15 minutes at discharge capacities of up to 22 milliampere hours per gram (mAh g-1). In combination with the averaged discharge potential of 3.6 volts, the devices can provide an energy density of 69 milliwatt hours per gram (mWh g-1) and a power density of 95 milliwatts per gram (mW g-1).

“Our system thus lays the foundation for more in-depth research and further developments in the area of organic photo batteries,” Wessling said.

The Cluster of Excellence Living, Adaptive, and Energy-Autonomous Materials Systems aims to combine the best of nature and technology, by developing lifelike materials systems inspired by nature. These systems adapt autonomously to their environment, harvest clean energy from their surroundings, and are insensitive to or able to recover from damage.

The research findings have been published in the journal Energy & Environmental Science.

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