Track and Trace: Unravelling the formation mechanism and charge carrier dynamics in AgBi-elpasolites

Abstract

In this PhD thesis we set out to understand the photoconversion performance of known and new halide-elpasolites semiconductors. Halide-elpasolites have been proposed as more stable and less-toxic alternatives for the remarkable performing lead-halide perovskites. The wide chemical variety and therefore highly tunable optoelectronic properties of this material class, provide a great platform for designing novel photoconversion materials. Cs2AgBiBr6 is one of the better-studied elpasolite compositions, which have resulted in various promising demonstrations in conversion applications. Compared to lead-halide perovskites, however, the effective conversion efficiency of Cs2AgBiBr6 falls short. In order to unravel the photoconversion efficiency of Cs2AgBiBr6 we tracked a journey of charge carriers through time. To achieve this, we combined different time-resolved spectroscopic techniques to trace the charge carrier population density and its mobility on timescales ranging from a trillionth of a second to several hours. To further improve the material design, we explored the mechanochemical formation mechanism and mechanical properties of alloyed AgBi-elpasolites. We identify the formation mechanism of new elpasolite compositions, such as Cs2AgBi1−y FeyBr6. The systematic exchange of the B’-site cation, provides an interesting approach to increase visible light absorption. In all, the insights presented in this PhD thesis will contribute to the synthesis and optimization of (new) elpasolites and inform on application design.