Humboldt Fellow will explore flexible semiconductors for energy harvesting

Alexander von Humboldt Foundation awards Kyuseon Jang

At a glance:

• Award: Humboldt Research Fellowship for Dr Kyuseon Jang, postdoctoral researcher at the Max Planck Institute for Sustainable Materials.
• Research topic: Conventional inorganic semiconductors are brittle, limiting their use in flexible and mechanically demanding applications. The aim is to understand why some inorganic semiconductors remain ductile at room temperature to develop flexible semiconductors for energy harvesting.
• Approach: Advanced electron microscopy, in-situ mechanical testing and atom probe tomography will be combined to directly observe how atoms and crystal defects move during deformation.
• Potential impact: The findings could enable more durable thermoelectric materials that convert waste heat into electricity while also reshaping our understanding of plasticity in inorganic semiconductors.

Most inorganic semiconductors are brittle and crack under mechanical stress. Yet, a recently discovered class of inorganic semiconductors can bend, stretch, and deform without breaking. The Alexander von Humboldt Foundation awarded Dr Kyuseon Jang, postdoctoral researcher at the Max Planck Institute for Sustainable Materials, a Humboldt Research Fellowship that supports his stay at the institute to reveal the atomic-scale mechanisms behind this unusual behaviour. The project aims to establish design principles for flexible and mechanically robust materials for future energy technologies.

When semiconductors behave like metals

Most engineering materials need to be able to deform without breaking. Metals achieve this through the movement of crystal defects, allowing them to bend or stretch while remaining intact. Semiconductors, by contrast, are usually much more brittle because their atomic bonds are stronger and more directional.

Over the past decade, researchers have discovered that some materials such as silver sulphide (Ag₂S) show an unexpected ability to deform plastically at room temperature. Silver sulphide is particularly promising because it is also a thermoelectric material, capable of converting waste heat directly into electricity. Flexible thermoelectric materials could one day power wearable electronics or recover waste heat from industrial processes.

Watching atoms move in real time

“Why do some semiconductors bend instead of breaking? Understanding this could open the door to more robust materials for sustainable energy harvesting. That’s the question I’m excited to explore during my Humboldt Fellowship”, says Jang. During the Humboldt Fellowship, Jang will investigate how plastic deformation occurs in silver sulphide and related materials. Using in-situ electron microscopy, he will directly observe the motion and interaction of crystal defects while the material is being mechanically deformed. Complementary techniques, including nanoindentation, micropillar compression, electron backscatter diffraction and atom probe tomography, will provide atomic-scale information about crystal defects, grain boundaries and local chemical changes.

The project will also examine how alloying silver sulphide with selenium or tellurium changes both its mechanical properties and deformation mechanism.

About the researcher and the fellowship

Dr Kyuseon Jang completed his PhD at the Korea Advanced Institute of Science and Technology (Korea). His doctoral research focused on revealing how microstructural heterogeneity influences thermoelectric performance. After a short postdoctoral phase at the same institute, he joined MPI-SusMat in March 2025, supported by a Max Planck Postdoctoral Scholarship, followed by a grant of the National Research Foundation of Korea and now receiving the Humboldt Research Fellowship.

The Humboldt Foundation fosters academic collaboration between exceptional international scientists and researchers in Germany. Its fellowships are awarded to individuals with outstanding qualifications and distinctive research profiles. The freedom for recipients to select any host institution in Germany makes this award a significant honour for both, the researcher and the hosting institute.