Combined Computational and Experimental Investigation on the Nature of Hydrated Iodoplumbate Complexes: Insights into the Dual Role of Water in Perovskite Precursor Solutions

Abstract

Water is generally considered an enemy of metal halide perovskites, being responsible for their rapid degradation and, consequently, undermining the long-term stability of perovskite-based solar cells. However, beneficial effects of liquid water have been surprisingly observed, and synthetic routes including water treatments have shown to improve the quality of perovskite films. This suggests that the interactions of water with perovskites and their precursors are far from being completely understood, as water appears to play a puzzling dual role in perovskite precursor solutions. In this context, studying the basic interactions between perovskite precursors in the aqueous environment can provide a deeper comprehension of this conundrum. In this context, it is fundamental to understand how water impacts the chemistry of iodoplumbate perovskite precursor species, PbI x 2– x . Here, we investigate the chemistry of these complexes using a combined experimental and theoretical strategy to unveil their peculiar structural and optical properties and eventually to assign the species present in the solution. Our study indicates that iodide-rich iodoplumbates, which are generally key to the formation of lead halide perovskites, are not easily formed in aqueous solutions because of the competition between iodide and solvent molecules in coordinating Pb 2+ ions, explaining the difficulty of depositing lead iodide perovskites from aqueous solutions. We postulate that the beneficial effect of water when used as an additive is then motivated by its behavior being similar to high coordinative polar aprotic solvents usually employed as additives in one-step perovskite depositions.

Lead-Free Metal Halide Perovskites for Hydrogen Evolution from Aqueous Solutions

“…The nature of the organic cation but, also, the strength of the bond between the central bivalent cation and the halide, have therefore a huge impact on these degradation path. Logically hydrophobic cations could protect the structure from the water entrance and strong metal halide bonds could offer superior resistance to the attack [52].…”

Formation of Lead Halide Perovskite Precursors in Solution: Insight from Electronic‐Structure Theory

“…The ability of in silico experiments to decouple the various effects in play has been exploited to interpret experimental data on the formation and the optical response of these systems. [21,[37][38][39][40] In addition, high-throughput screening has been proven as a reliable and cost-effective method to explore large configurational spaces in view of the synthesis and characterization of these complex materials. [21,41] Motivated by these successful contributions from theory, in this work, we want to further explore the formation of LHP solution precursors adopting a physicists' perspective.…”

The Challenge of Ambient Air–Processed Organometallic Halide Perovskite: Technology Transfer From Spin Coating to Meniscus Blade Coating of Perovskite Thin Films

“…Because of the chemical complexity of the precursor solution, the presence of oxygen and moisture in ambient air results in an uncertainty of the precursor recipe developed for the glovebox process to be transferred to the ambient process. Water molecules attack the perovskite film by forming the (CH 3 NH 3 ) 4 PbI 6 di-hydrated phase and PbI 2 via the chemical reaction (Radicchi et al, 2020)…”

“…The release of two water molecules provides the self-sustainability of the chemical reaction process, resulting in the degradation of the complete perovskite film. Computational studies also showed that aqueous solutions inhabited the formation process of perovskites, but small amount of water could be added as an additive for the deposition of perovskite materials (Radicchi et al, 2020). A study has been conducted recently to provide a comprehensive understanding of the improvement of PSC stability against water molecules through compositional engineering (Li et al, 2021).…”