Meidan Auditorium and by Zoom
Double perovskite (elpasolite) structures with Cs2AgBiBr6 composition were suggested as an emerging inorganic semiconductor for solar energy conversion. We show how colloidal synthesis provides a methodological basis for investigating these materials and their transformation from a single monolayer into a bilayer structure (by Cs addition), and finally to thicker nanoplatelets (by heating). In our work, we study each derivative’s structural, compositional, and morphological properties to elucidate the common growing mechanism. The monolayer and bilayer’s thermal stability are investigated, and thermal expansion coefficients are extracted using in-situ temperature-dependent XRD measurement (up to 290°C). Our methodology enables the use of HRTEM and, specifically, a non-trivial Moiré pattern visualization STEM (scanning transmission electron microscopy) technique, which magnifies structural defects and allows their detection. We will discuss a typical structural defect of these nanoplatelets in the form of voids accompanied by stacking faults. We hypothesize these defects are reminiscent of an oriented attachments formation step accentuated in the final annealing step of the synthesis. Our findings will bring these materials one step closer to the application by suggesting rational engineering techniques for controlling electronic properties of bismuth-based lead-free double perovskites.
Supervisor: Dr. Yehonadav Bekenstein