Metal halide perovskite materials are among the most exciting materials for optoelectronic applications, with solar cells being a particularly promising area of research. One of the most attractive features of these materials is the convenient solution processing at mild temperatures, which can be applied to the most diffuse printing techniques. The perovskite precursor solutions consist of a colloidal suspension of ionic species, whose reactivity and complexation, together with the viscosity and surface tension of the inks, all contribute to the formation of a perovskite film with the desired properties. The study and control of the perovskite precursor inks is therefore fundamental to master the formation of the material, which occurs through an inherently disordered self-assembly process, and thus the optoelectronic quality of the resulting perovskite films.
This talk will first give an overview of the evolution of the precursors to the final perovskite film formation, correlating the solution chemistry of the inks and the final film structure. Particular emphasis will be placed on the formation of intermediate species during solution aging and how these species can affect final film formation and photovoltaic device properties. Additive engineering will then be proposed as an effective strategy to control the nano/microscale morphology and optoelectronic quality of the perovskite material via wet processing. It will be shown that weak interactions established by molecular or macromolecular additives and the organic cations already in the precursor mother solutions can interfere with the nucleation and growth processes of the perovskite polycrystalline films, ultimately affecting their optoelectronic, mechanical, structure and stability.