Advent calendar - December 7th - Sander Heester

In the Zernike Institute Advent Calendar, we are presenting 24 short spotlights in December. In these specials, we highlight PhD students, postdocs, support staff and technicians of our research groups and team - providing a glimpse into their typical day at work. In Episode 7 meet Sander Heester, PhD researcher in the Physics of Novel Semiconductors and Devices of Prof. Jan Anton Koster.

I am a PhD student in the group of Jan Anton Koster, currently entering the final year of my PhD. My research focuses on numerical modelling of charge transport in semiconductors using the drift-diffusion model, with a special focus on perovskite solar cells. These materials are rising stars in the solar-energy world, yet many challenges remain to be solved. With our modelling work, we aim to deepen the understanding of the electrical processes inside these devices and identify how to overcome their current limitations.

A key part of my work is bridging the gap between numerical simulations and experiments. I strongly believe that the greatest progress happens when both perspectives come together, which is also why we often collaborate with several European partners to develop ever better and more durable perovskite solar cells. During my PhD, I work on a wide range of topics: developing a new experimental technique, extending and improving our own model SIMsalabim, translating experiments into numerical implementations, and increasingly using machine-learning models and algorithms. One of my favourite projects has been building a graphical user interface that allows anyone to run the complex simulations directly from their browser, all running on a server just in our office!

Most of my days are spent sitting behind my computer: running simulations, analysing devices, and, lately, as any PhD student writing a lot. Occasionally I get to enjoy sharing our expertise and experiences by teaching and supervising students. All this often comes with a well-deserved coffee break, a casual lunch, or a (not so) scientific discussion with my fellow PhDs or Jan Anton. Outside the office, I love travelling, reading fantasy book series, and I’m always up for a good board game.

See all Advent Calendar items 2025 here!