Over the past ten years, interest in metal halide ABX3 perovskites has skyrocketed, with lead halide perovskites (LHPs) dominating application development in cutting-edge photovoltaics (PVs). The best-performing perovskite solar cells (PSCs) recently exceeded 25% photoconversion efficiency (PCE) while a tandem LHP/c-Si solar cell demonstrated &gt;29% PCE demonstrating tailorable optoelectronic properties. LHPs nevertheless come with toxicity issues due to the presence of Pb in these materials and their byproducts, which has prompted researchers to look for substitute materials that perform equally well. Germanium-based perovskites could emerge as promising candidates for LHP substitutes. The optical bandgap of CsGeI3 (1.6 eV) in particular is ideally suited for solar spectrum absorption in the visible range. However, the development of germanium halide-based PV applications has so far been slower than that of other perovskites, with only modest PCEs (as high as 7.9%) documented. Understanding these compounds in detail is essential for maximizing the potential of novel materials in solar applications and raising PCEs even further. This objective can only be achieved with a thorough understanding of the functions that atomic structure, defects, and dynamics play in the bulk properties of these lead-free solar materials. Although there have been theoretical investigations on CsGeX3, experimentally probing the electronic structures of these materials is essential to reach the goal of matching LHP devices. Photoemission spectroscopy (PES), an experimental technique based on the photoelectric effect, could be one the most powerful methods in this regard. However, we require microcrystals (&gt;100 mm) rather than nanocrystals to conduct PES on these solids. This study aims to advance our previously reported synthesis of CsGeX3 nanocrystals to microcrystals to acquire further experimental insight into their electrical structures.

Towards experimental investigation of the electronic structure of germanium-based perovskites

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