Atomic Layer Deposition Increases Efficiency of Nighttime Solar Cells

A promising new process, known as Atomic Layer Deposition, could potentially improve existing solar energy systems.

The new technique has been invented by Brian Willis, an associate professor of chemical and biomolecular engineering at the University of Connecticut and the former director of UConn’s Chemical Engineering Program. He explored the so called rectennas, or nano-antennas, which in theory could harvest more than 70% of the sun’s electromagnetic energy, but in practice scientists have still not developed the needed technology.

The main reason behind this is that these rectennas must be able to operate at the speed of visible light and their core pair of electrodes should not be more that 1-2 nanometers apart. The latter is particularly important because it creates an ultra-fast tunnel junction between the two electrodes and allows a maximum transfer of electricity.

Professor Willis developed a ground-breaking technique, called selective area atomic layer deposition (ALD). Here, the two interior electrodes have sharp tips, which are placed at the needed distance. Such space was not achievable before the ALD technique was developed. Willis demonstrated that he could now coat the tips of the rectenna with layers of copper atoms until the desired distance is made.

Made this way, the rectennas could convert solar radiation in the infrared region through the short wavelengths of the visible light. In addition, the rectenna device does not depend on a band gap, which means that it could harvest light throughout the whole spectrum.

The invention won the team of scientists at Penn State Altoona- led by physics professor Darin Zimmerman, together with professor Willis, a grant of $650,000 for the next three years from the National Science Foundation.

According to the scientists, this solar power conversion device could potentially create a revolution in green solar power technology, increasing the efficiency and reducing the cost.

ALD is a completely innovative process and as Zimmerman states it would also help understanding the physical processes behind the devices. The process is simple and very easy to reproduce. It is also applicable and could improve other areas too including current photovoltaics, thermoelectrics, infrared sensing, chemical sensors and more.

The aim for the next three years is to have a working prototype of a rectenna so that they can begin testing the efficiency.