Perovskites for optoelectronic applications: new synthetic approaches and properties modulation routes

The development and the increasing application of renewable sources are two pivotal points of the solutions set for the huge climatic challenge that all the world is facing nowadays. Apart from the classical silicon-based photovoltaic panels, one of the most flourishing fields is that of metal halide perovskites (MHPs). The enormous attractiveness of MHPs relies on their outstanding optoelectronic properties and their applicability in many different fields. Their extreme tunability is due to their structure, and consequently their properties' ease of modification. All MHPs are constituted by a network of octahedra: when they share 6, 4, 2, and 0 corners the structure is respectively called 3D, 2D, 1D, and 0D perovskite, with 3D being the most efficient. However, even though only limited amounts of Pb are implemented in solar cells, there is a potential risk of harm to humans and the environment. Therefore, researchers are currently trying to substitute Pb with other suitable elements to develop novel, low-cost, non-toxic, and environment-friendly perovskite materials, that could be possibly capable of various applications with superior performances and long-term stability. In almost all the devices, the perovskite is present in form of thin film, therefore in literature many different growing methods can be found, either solution or vapor-based. Solution based ones are the most applied, but even the optimized techniques are affected by many shortcomings, such as: a lack of control over the low-temperature crystallization process, which is affected by many factors and often leads to poor reproducibility in properties; the solvent employed in depositing a perovskite layer washes away the underlying ones, so the sequential film deposition and the deriving perovskite-perovskite heterostructures are very difficult to realize; the complex fluid dynamics during the scale-up of solution methods do not permit the growth of uniform thin films in panel-size substrates due to the many intermediate phases that coexist during the crystallization process; the common wet-chemistry protocols used for hybrid phases do not assure good results in totally inorganic perovskite deposition, mainly because of the poor solubility in polar solvents of many halide precursors. The main aims of this thesis are: the realization of new approaches to tune, in a stable way, the optical and structural properties of perovskites in order to extend their range of applications; the development of different environmental-friendly scale up methods suitable to prepare perovskite phases for optoelectronic devices and to stabilize metastable phases. For these purposes, we focused on industrial types of equipment and techniques that could fit our scopes. The first part of this work is about employing and optimizing a vapor-based technique to deposit metal halide perovskites thin films. The most employed physical vapor deposition method consists of different variations of thermal evaporation, therefore we decided to explore radio-frequency magnetron sputtering because of the advantages of simple equipment, easy control, large coating area, and strong adhesion. By means of this technique, a large number of thin films can be prepared at relatively high purity, high speed, low temperature, and low cost. The second section focuses on preliminary in-situ high-pressure studies of metal halide perovskites at large facilities. This investigation of MHPs is relatively recent and, while studies of temperature dependence modification and chemical tuning strategies exist, the knowledge of pressure-induced effects remains scarce. These studies could allow us to more precisely tune the properties through compression and also permit the discovery of new phases that subsequently could be stabilized at ambient conditions. The last part of this work is focused on the tuning of MHPs by the means of two industrial physical modulation techniques: spark plasma sintering and ball-milling.