Understanding halide perovskite solution chemistry

Solution synthesis is one of the most commonly employed method to prepare metal-halide perovskites for optoelectronic applications. A controlled perovskite growth from solution is crucial to obtain high quality materials and requires a deep understanding of the perovskite precursors chemistry. In fact, the choice of the starting materials (salts, solvents, additives) dictates the final morphology and crystallinity of the perovskite itself.

Identifying the composition of solvated iodoplumbates (i.e., lead-iodide complexes), which are formed during perovskite solution preparation, is then of great relevance to link solution and material properties. Particularly, uncovering the effect of solvents and additives on the iodoplumbates equilibria would let us go a step further in understanding the behavior of these materials.

To meet this goal, researchers at the University of Perugia and CNR-SCITEC, developed a combined experimental and computational framework, which comprises UV/Vis absorption spectroscopy and Density Functional Theory (DFT) simulations. Static calculations and molecular dynamics were used to unveil the structural properties of modeled solvated iodoplumbates, that were then taken as starting points for Time Dependent DFT calculations featuring spin-orbit coupling (SOC) effects (SOC-TDDFT) for the accurate simulation of their optical behavior.

The excellent agreement between theoretical and experimental absorption spectra led the researchers to uncover the plausible solvated perovskite species with coordinating solvents. In a series of papers, the solvated structures in such as dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), [1] and γ-butyrolactone (GBL), [2] have been reported. The effect of water [3] and the PbCl2 lead salt precursor [4] on the iodoplumbates equilibria have also been studied by comparing experimental spectra with calculated ones. These studies shed light on how the nature of solvated complexes is influenced by the different components of perovskite precursors solutions, which have direct consequences on the way perovskites grow, the morphology, and the type of defects that will be found in the final material, affecting its performance in solar cells.

Solvated perovskite TDDFT input examples: GUI, run file

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[1] Radicchi, E.; Mosconi, E.; Elisei, F.; Nunzi, F.; De Angelis, F. Understanding the Solution Chemistry of Lead Halide Perovskites Precursors. ACS Appl. Energy Mater. 2019, 2, 3400–3409.

[2] Radicchi, E.; Kachmar, A.; Mosconi, E.; Bizzarri, B.; Nunzi, F.; De Angelis, F. Structural and Optical Properties of Solvated PbI2 in γ-Butyrolactone: Insight into the Solution Chemistry of Lead Halide Perovskite Precursors. J. Phys. Chem. Lett. 2020, 11, 6139–6145.

[3] Radicchi, E.; Ambrosio, F.; Mosconi, E.; Alasmari, A. A.; Alasmary, F. A. S.; De Angelis, F. Combined Computational and Experimental Investigation on the Nature of Hydrated Iodoplumbates Complexes: Insights on the Dual Role of Water in Perovskite Precursor Solutions. J. Phys. Chem. B, 2020, 124, 11481–11490.

[4] Kaiser, W.; Radicchi, E.; Mosconi, E.; Kachmar, A.; De Angelis, F. Iodide vs Chloride: The Impact of Different Lead Halides on the Solution Chemistry of Perovskite Precursors. ACS Appl. Energy Mater. 2021, 4, 9827–9835.

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