For a chemistry undergraduate focused on synthesis, pivoting to a PhD in physics is a bold move. But that’s exactly what Sascha Feldmann did—unlocking a research career that fuses materials science, photonics, and quantum physics.

Feldmann’s group at the Swiss Federal Institute of Technology, Lausanne (EPFL), probes the fundamentals of light, charge, and symmetry to boost solar photovoltaics, build energy-efficient electronics, and develop quantum information technologies.

Feldmann, who grew up in a sleepy village in northern Germany, had a childhood passion for baking that transferred seamlessly to the synthesis lab during his undergraduate studies at Heidelberg University. This led him to a 9-month exchange program in 2015–16 making air-sensitive phosphorus compounds in the chemistry department at the University of Cambridge.

But he was intrigued by the work in the physics labs next door: “I got a bit jealous that they had all the fun of playing with the materials we were making,” Feldmann says.

“He was curious about the physics aspects of materials and was able to connect his chemistry background with all the new things he had to learn about physics,” recalls Felix Deschler, who supervised Feldmann’s PhD at Cambridge and is now at Heidelberg University. “That curiosity, and the ability to combine these two fields, made him stand out.”

Feldmann returned to Cambridge in 2017 for a PhD studying the semiconductor physics of perovskites—the light-absorbing material in thin-film solar cells that are just starting to come to market. Perovskites can also serve as the active materials in light-emitting diodes (LEDs), and Feldmann’s research helped show that the materials’ disordered structures can actually make them more efficient. Feldmann continued working with what he calls “messy” perovskites at the Rowland Institute at Harvard before moving to EPFL in 2024.

One of Feldmann’s goals is to improve the efficiency of solar cells. When light hits a photovoltaic material, it frees electrons and positive “holes” that must travel to opposing electrodes to generate a current. If the charges recombine before reaching their destinations, the energy they carry is squandered.

But these electrons and holes don’t have just opposite charges but also opposite spins. Introducing asymmetry into the perovskite’s structure can make spin-up and spin-down charges flow through the material in different ways. Physicists call that approach symmetry breaking, “but for an organic chemist, that means chirality,” Feldmann explains. So he is using chiral components in perovskites or adjacent layers to control electrons and holes via their spins. “If we could improve the way charges are being removed from each other—electrons one way and holes the other—that would be really beneficial for device efficiency,” he says.

Symmetry breaking could also help LEDs, which bring electrons and holes together to generate light. Feldmann has found that seeding metal ions in perovskite nanocrystals can boost the nanocrystals’ luminescence—not via chemical or electronic effects but by introducing asymmetries that help the charges come together.

To enable more-efficient electronic displays, Feldmann’s team is now trying to create LED materials that emit circularly polarized light, whose waves spiral like a left- or right-handed corkscrew. Conventional LEDs emit nonpolarized light, half of which is typically absorbed by antiglare filters used on the screens of laptops, smartphones, and TVs. Using suitably polarized light instead could cut those losses at a stroke, Feldmann says. “We would double the efficiency of existing displays, just by making this a chiral emission of light.”

Meanwhile, he’s using polarized light to control spins in perovskites, creating regions enriched in either spin-up or spin-down electrons. If Feldmann’s team can manipulate these regions, it could enable a fresh approach to spintronics—an emerging quantum IT that encodes and processes data using spin rather than charge to cut the energy consumption of computing.

It’s all a long way from baking cakes, and Feldmann recognizes that working across multiple disciplines can throw up language barriers as colleagues wrestle with unfamiliar jargon. But he relishes the communication challenge: “If I'm not able to convey what I'm working on and why it's interesting, then I'm doing something wrong.”