The recent discovery of hybrid organic-inorganic metal halide perovskites led to a renaissance of thin film photovoltaics. The great diversity of hybrid perovskite compositions and preparation pathways makes them an excellent candidate for novel photovoltaic materials with unique combination of properties, the potential for low cost and easy processing along with relatively high power conversion efficiencies. In the last few years, perovskite solar cells have leapt from 10% to a certified value of 22.7%. This spectacular rise in cell performance attracted intense attention from the scientific community. The promise of perovskites in accessing these technologies is on account of their unique properties, which can be tuned on the nanoscale. Crystallinity, density of defects and impurities are key factors for optoelectronic properties, and are also highly dependent on the materials formation processes for most inorganic semiconductors. Understanding this behaviour and the structure/property relationship is crucial for fundamental understanding of perovskite materials, and for extending their properties to other process-tolerant systems.
The overall objectives of MatchForSolar project fit squarely into current trends in photovoltaic research. More specifically, the developed mechanochemical approach relying on simple grinding of the precursors has emerged as a straightforward and reliable method for preparing large quantities of perovskites. Mechanosynthesis of perovskites allows the introduction of inorganic (A-site cations, B-site metals, X-site anions) as well as organic (passivation agents) species in a controllable manner, both on molecular and nanoparticulate level. Developing a novel, solvent-free synthetic procedure based on grinding in the solid state provides a faster, cleaner and more robust alternative to the solution-based method. The mechanochemical approach also provides an efficient general method for incorporating poorly soluble salts into multi-component perovskite crystal lattices. These studies give an evident possibility for a more in-depth understanding of mechanochemical processes occurring in the solid state.
In addition, mechanochemistry allows the facile synthesis of large quantities of polycrystalline materials that is particularly well-suited for solid-state NMR studies, which can provide direct information about cation dynamics and atomic level phase compositions. For example, 133Cs, 87Rb, 39K, 13C, 2H and 14N solid-state MAS NMR was used to directly probe microscopic composition of Cs-, Rb-, K-, MA-, and FA-containing phases in double-, triple-, and quadruple-cation lead halides in bulk and in thin films. Notably, it has been shown that the structure of bulk mechanochemical perovskites is indistinguishable from that of thin films, making them a good benchmark for structural studies with high sensitivity. These studies highlight the essential need for atomic-level characterization of photovoltaic perovskite materials and provide fundamental understanding of photovoltaic parameters in these systems and their superior stability.
The subjects proposed in MatchForSolar project also include fabrication and photovoltaic characterization of perovskite solar cells. The obtained results demonstrate that the direct thin film crystallization from the lead-based mechanoperovskite is a promising method for achieving solar cells with less hysteresis. This study also opens up new possibilities for the efficient and sustainable synthesis of other lead and lead-free hybrid halide perovskites.
