Photovoltaics – or solar cells – are devices that transform sunlight into electrical energy. Due to the increasing global importance of abundant renewable energy sources, development of more efficient and cheaper solar cells is a very important research area. In our group we focus on silicon-based solar cells. Silicon is the second most abundant element on Earth and silicon is by far the most used material for commercial solar cells. The cost of electricity from silicon solar cells has decreased exponentially over the last couple of decades and is now cost-competitive with other energy sources in many countries. However, in order to improve the cost-efficiency even further and ensuring that solar energy can be scaled to the multi-TW level (1000’s of GW), there is a need to make new solar cell designs using smarter, scalable methods and abundant materials. In our group we target this from several different angles; focusing on surface texturing and laser doping of cells, but also novel advanced cell structures such as tandem and triple-junction cells based on conventional and ultrathin silicon.
Specifically, we focus on micro- and nanostructured surfaces that increase the optical absorption and thereby the efficiency of the solar cells. An example is ‘black silicon’, which is simply nanostructures etched into silicon in a dry, 1-step etching process. These surfaces suppress the optical reflectance loss from solar cells to below 1% over the entire relevant solar spectrum.
A different branch of our research focuses on photovoltaic retinal implants for blind patients. Millions of patients worldwide are blind due to degenerated photoreceptors. This includes patients suffering from AMD (age-related macular degeneration) and retinitis pigmentosa. Since photoreceptors work somewhat like solar cells; by creating small electrical signals from the incoming light, we aim to mimic the photoreceptor function in an implantable device with thousands of small solar cell units. The final goal is that such a chip can be implanted behind the retina (subretinal) and when the chip is illuminated with an LED from outside the eye, the chip produces small electrical signals delivered to the neurons. If the brain is able to interpret this signal, blind patients may regain part of their vision with such an implant. We are currently fabricating the 2nd version of the chip – in close collaboration with DTU Nanolab – and continuously testing the functionality on fresh retinal tissue from pigs at Aarhus University Hospital.