Living on the edge: what is the nature of the bandgap in metal halide perovskites?


Metal halide perovskite (MHP) semiconductors, such as methylammonium lead iodide (MAPbI3), have recently received tremendous attention in materials science, as these have yielded high efficiency solar cells, X-ray detectors and LEDs. However, one of the most fundamental material properties of MHPs still remains unclear: whether their bandgap is direct or slightly indirect. The nature of the bandgap determines the charge carrier lifetime, which influences important properties of MHP-based devices such as the voltage of solar cells and the light emission properties of LEDs. This project aims to reveal the nature of the bandgap and investigate whether this can be manipulated, which will be crucial for rational design of MHP-based devices. To study the nature of the bandgap, I will develop a unique pressure- and temperature-dependent photothermal deflection spectroscopy (pt-PDS) set-up. This is the most suitable technique to probe the band-edge absorption in MHPs as it ignores reflection and hence measures about four orders of magnitude more sensitive than regularly used UV-VIS transmission measurements. These pt-PDS measurements will enable me to disentangle an indirect bandgap from contributions of excitons and trap states, since these all evolve differently with temperature and pressure. This project will result in the first demonstration of the temperature- and pressure-dependent band-edge absorption in MHPs. Hence, I will find either the presence or the absence of a slightly indirect bandgap, which cannot be exclusively determined using conventional absorption techniques. Additionally, I will contribute to a deeper understanding of the band-edge absorption as function of temperature, pressure and composition, which will be vital for rationally optimizing MHPs for each envisioned application. Finally, this project not only addresses an important research question, but also yields a unique experimental set-up, which I expect to be valuable for studying other fundamental properties of semiconductor materials.





Dr. E.M. Hutter

Verbonden aan

NWO-institutenorganisatie, AMOLF, Hybrid Solar Cells


01/09/2019 tot 01/09/2022