Fiona Treber: Ternary Metal Sulphide Nanocrystals for Photovoltaic Applications

Abstract

Semiconducting nanocrystals (NCs) have attracted a significant amount of attention for optoelectronic applications in general and photovoltaics in particular over the last decades, due to the tunability of their properties. However, many high-performing and well-studied materials contain toxic elements, such as lead or cadmium. As a result, efforts were made in finding other more environmentally friendly compounds. Two promising candidates that were identified are AgBiS2 and NaBiS2, which are at the centre of the research summarized in this thesis.

The main aspect studied herein with respect to both compounds is their passivation, which has a significant impact on the material properties and device characteristics. For AgBiS2, investigations into ligand treatments containing different halides are presented and their effect on the solar cell performance is discussed. Findings from photoelectron spectroscopy (PES) measurements show that ligand incorporation into the fabricated thin films drops off significantly from iodide to bromide and chloride, but still the bromide-capped NCs result in the best working devices. Furthermore, when considering both iodide- and thiol-treated AgBiS2 particles, significant differences in charge carrier separation across the interfaces with the adjacent charge transport layers can be observed. In addition to these passivation-focused studies, AgBiS2 NCs are also tested with respect to applications beyond the classical solar cells, with a particular focus on lower temperature black body radiation in a hypothetical photon glow battery setup. Lastly, prospects and challenges of implementing NaBiS2 NCs in solar cells are discussed. Device testing coupled with PES studies showed that this material requires not only surface but extended passivation throughout the particle to realise functional devices.

Overall, this work provides new insights into the how these passivation effects impact the device performance, while also taking a brief look at new concepts for combined energy conversion and storage.