Metal halide perovskites: from microstructure to optical properties
Metal halide perovskites are semiconductors that hold great potential for a variety of different optoelectronic applications. By changing the ions that make up the perovskite lattice, the properties of these materials can be adjusted to fit specific applications, such as solar cells or light-emitting diodes. Besides, these materials can be processed directly from solution, which enables the use of large scale and cost-effective deposition techniques.
In this thesis, the microstructure and optical properties of metal halide perovskites are studied using optical spectroscopy and structural characterization techniques. First, we demonstrate that defects at the surface of single crystals of methylammonium lead tribromide can be permanently passivated by benzylamine, and that this procedure is accompanied by an unintended cation exchange reaction. Secondly, we assess the quality of films cast using a scalable blade coating procedure. 2D perovskites cast in this way are highly crystalline in nature, but suffer from heterogeneous properties on a microscopic scale. Attempts to control the crystallization of mixed 2D/3D perovskite films furthermore underline the complex energetic landscape posed by these material systems. The effectiveness of two different methods to obtain high-quality 2D/3D perovskite films with desired optical and crystallographic properties are assessed and recommendations concerning their processing are put forth. Finally, fundamental material parameters of layered 2D perovskites based on lead and tin are accurately determined using magneto-absorption measurements. The obtained values for the exciton binding energy, bandgap and reduced effective mass of charge carriers serve as a reference for the perovskite field.
See also: Treating Solar Cell Materials Reveals Formation of Unexpected Microstructures