Perovskite solar cells have electrified the solar cell research community with astonishing performance and surprising material properties. However, the widespread commercialization of perovskites in solar cells and other optoelectronic applications still requires a more detailed knowledge about fundamental material properties. My group is specialized in the investigation of these properties on nanometer length scales using scanning force microscopy.
We recently discovered a distinct nanoscale stripe domain structure in MaPbI₃ perovskite crystals using piezoresponse force microscopy (PFM). The pattern is characteristic for ferro-elastic twin domains. Using a combination of PFM and photoluminescence microscopy, we found that this domain structure leads to an anisotropic charge transport across the crystal. To visualize the functionality of different layers, we developed a method to prepare smooth cuts through a solar cell device. We subsequently map the potential distribution across the device using time-resolved Kelvin probe force microscopy (tr-KPFM). We could show that the formation and release of ionic interface charges determine the time scales for current-voltage hysteresis in perovskite solar cells. Our results highlight that precise control over interfaces in perovskite solar cells is the key, not only for controlling and suppressing hysteresis but also for their long-term stability in perovskite solar cells.

Visualization of the anisotropic diffusion along ferroelastic domain walls in MaPbI<sub>3</sub> perovskite. The structure in the background is a 3D rendered image of the perovskite grain overlaid with the domain pattern as observed by PFM.

Visualization of the anisotropic diffusion along ferroelastic domain walls in MaPbI₃ perovskite. The structure in the background is a 3D rendered image of the perovskite grain overlaid with the domain pattern as observed by PFM.

Stefan A.L. Weber

Prof. Dr., MPI for Polymer Research Mainz, Germany

Appearances