Faculty of Science, Technology and Medicine
Faculty of Law, Economics and Finance
Faculty of Humanities, Education and Social Sciences
Interdisciplinary Centre for Security, Reliability and Trust
Luxembourg Centre for Systems Biomedicine
Luxembourg Centre for Contemporary and Digital History
Luxembourg Centre for European Law
Luxembourg Centre for Socio-Environmental Systems
Solar panels are everywhere, but did you know that a significant part of the sunlight they receive still goes to waste? Prof. Susanne Siebentritt and her team at the University of Luxembourg are developing a new generation of solar cells that could change that. Their tandem solar cells are incredibly thin and efficient, converting more sunlight into electricity than traditional panels.
Why current solar cells aren’t enough
Today, conventional solar cells can convert typically less than 25% of the sunlight they receive into electricity. Why so little? Imagine single cyclists pedaling their bikes. They can only go so fast on their own. Now picture two cyclists riding a tandem bike: together, they can pedal farther and faster. Tandem solar cells work in a similar way. By stacking two layers of semiconductor, each capturing different parts of sunlight, they combine their energy to produce more electricity than a single layer ever could.
Even tandem cells, however, lose some energy. Prof. Siebentritt’s team investigates exactly where these losses occur to understand their causes. By measuring the light emitted by the solar cell’s semiconductor layer—the part that absorbs sunlight and generates electricity—they can pinpoint energy losses even before the cell is fully built.
A barrier that helps and hinders at the same time
One feature the team studies is the intentional compositional gradient, a deliberate change in the material across the layer. This gradient helps direct electron flow, improving current generation.
However, it also introduces energy losses that reduce the cell’s voltage. Accurate measurements reveal where the losses occur. With this information, the team can fine-tune the gradient’s design to maximise benefits and limit drawbacks.
‟ “The tools we use to understand the losses in solar cells are very helpful to develop stable tandem solar cells. We are all very excited to contribute to the future of solar cells.” ”
Professor in Physics
The future of solar energy
Commercial solar cells are getting better in efficiency all the time. The team will produce tandem cells in the coming years to continue this trend. The solar cells investigated in Prof. Susanne Siebentritt’s team can become the tandem partner for conventional solar cells in the future. They are particularly interesting because they maintain their efficiency under real world conditions for decades.
Prof. Susanne Siebentritt and her team are also exploring designs without compositional gradients. These innovations have already led to record efficiencies, which is very promising for the future. “These record efficiencies and our tools to understand the losses in solar cells are very helpful to develop stable tandem solar cells. We are all very excited to contribute to the future of solar cells” says Prof. Susanne Siebentritt.
Looking ahead, Prof. Siebentritt aims to optimise alternative cell designs. New projects also aim to make the back layer of the solar cell see-through. This design allows the cell to capture light from the backside. Additionally, this lets the team use light-based measurements to see exactly where energy is lost inside the cell, helping them improve performance even further.
The scientific journal PRX Energy recently published this study. The solar cell has also been included in the recognised efficiency tables for photovoltaic devices.