*ZOOM* [PhD Thesis Presentation] - Mr. Andrew Justin Winchester "Spatially and temporally resolved microscopy of traps in hybrid organic-inorganic perovskites"
Presenter: Mr. Andrew Justin Wichester
Supervisor: Professor Keshav Dani
Unit: Femtosecond Spectroscopy Unit
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Title: Spatially and temporally resolved microscopy of traps in hybrid organic-inorganic perovskites
In recent years the class of materials known as hybrid organic-inorganic perovskite (HOIP) have received notable attention for use in photovoltaic applications, with record solar conversion efficiencies reaching other established thin film systems. Despite their rapid development, there are still ongoing issues related to heterogeneous film properties which limit device performance. It has been suggested that sites which capture charge carriers (traps) could be localized on a micrometer or smaller size scale, leading to regions of poor efficiency. Understanding the electronic properties of such regions, in particular on how they influence carrier recombination, will therefore provide crucial information about the carrier loss pathways in HOIP films, which will be essential for developing new strategies to minimize losses and create more efficient devices. In order to gain information about the ultrafast charge carrier recombination dynamics on nanoscale length scales, specialized techniques which can provide information with both high spatial and temporal resolution will be necessary. Here, we utilize time resolved photoemission electron microscopy (TR-PEEM) as a novel technique to study the nanoscale ultrafast properties of photo excited carriers and their relation to heterogeneous film properties in HOIP thin film materials. Following this overall theme, the work in this thesis will address several nanoscale properties and phenomenon. First, we will uncover the nanoscale distribution of carrier traps in a HOIP film which result in non-radiative losses. We then will describe in depth the ultrafast carrier trapping processes happening at nanoscale trap clusters. Following this, we will then discuss other novel information and studies on the traps in HOIP which can be realized using TR-PEEM, namely on effects of light treatments and morphological information. By gaining a deeper understanding in these directions, we hope to contribute to the broader goal of improving HOIP photovoltaic device efficiency and showcase TR-PEEM as a novel technique for studying photocarrier dynamics in semiconductor materials.