Understanding the Solution Chemistry of Lead Halide Perovskites Precursors

Abstract

Identifying the composition of the solvated iodoplumbate complexes that are involved in the synthesis of perovskites in different solution environments is of great relevance in order to link the type and quantity of precursors to the final optoelectronic properties of the material. In this paper we clarify the nature of these species and the involved solution equilibria by combining experimental analysis and high-level theoretical calculations, focusing in particular on the DMSO and DMF solvents, largely employed in the perovskites synthesis. The specific molecular interactions between the iodoplumbate complexes, [PbIm] 2-m , and the solvent molecules, X, were analyzed by identifying the most thermodynamically stable structures in various solvent solutions and characterizing their optical properties trough DFT and TD-DFT calculations. A comparison with the experimental UV-Vis absorption spectra allows for the first time the definition of the number of iodide and solvent ligands bonded to the Pb 2+ ion and of the complex formation constants of the involved species.3

Room‐Temperature Partial Conversion of α‐FAPbI3Perovskite Phase via PbI2Solvation Enables High‐Performance Solar Cells

“…The four states of PbI 2 revealed in our previous investigation are summarized in Figure 1b The solution‐casting of PbI 2 from a DMF solution results in the sequential formation of different solvated states during solution drying in the PbI 2 sol‐gel process in DMF, as revealed by in situ GIWAXS measurements. A disordered colloidal state (P 0 ) without a diffraction signature is observed for t < 20 s. A metastable solvated phase (P 1 ) is observed for 20 s < t < 60 s. This metastable phase transitions to a second metastable solvated phase (P 2 ) for 50 s < t < 300 s, which subsequently converts into crystalline PbI 2 as of t > 300 s. Determining the exact structure of those intermediate crystalline complexes, however have been very challenging since the solvate phases feature only a very limited number of reflections in GIWAXS, which is not sufficient for a structure determination . Representative GIWAXS snapshots taken immediately after FAI loading and spin‐off (Figure 1c and after the IPA wash (Figure 1d for the four scenarios reveal the formation of 3D powder rings corresponding to the (110) reflection of the perovskite α‐FAPbI 3 phase ( q ≈ 10 nm −1 ) in all cases.…”

“…A disordered colloidal state (P 0 ) without a diffraction signature is observed for t < 20 s. A metastable solvated phase (P 1 ) is observed for 20 s < t < 60 s. This metastable phase transitions to a second metastable solvated phase (P 2 ) for 50 s < t < 300 s, which subsequently converts into crystalline PbI 2 as of t > 300 s. Determining the exact structure of those intermediate crystalline complexes, however have been very challenging since the solvate phases feature only a very limited number of reflections in GIWAXS, which is not sufficient for a structure determination. [72,73] Representative GIWAXS snapshots taken immediately after FAI loading and spin-off ( Figure 1c and after the IPA wash ( Figure 1d for the four scenarios reveal the formation of 3D powder rings corresponding to the (110) reflection of the perovskite α-FAPbI 3 phase (q ≈ 10 nm −1 ) in all cases. However, the (010) reflection of the yellow nonperovskite δ-FAPbI 3 phase (q ≈ 8.6 nm −1 ) is prominent for P 1 and c-PbI 2 and weakly formed for P 0 and P 2 , and almost disappears after the IPA wash step for the P 2 case (the intensity is negligible in comparison with the perovskite intensity), while only weakening for P 1 and PbI 2 cases.…”

The nature of the lead-iodine bond in PbI2: A case study for the modelling of lead halide perovskites

“…Upon solvent evaporation, a polycrystalline MAPbI3 film is generated. It is well established that the chemical interactions between the organic and the inorganic components, both in the precursor solution and in the solid state, strongly affect the formation, the optoelectronic properties and the stability of the perovskite materials, that final influence the solar cell efficiency and stability [9].…”

Investigating the effect of solvent vapours on crystallinity, phase, and optical, morphological and structural properties of organolead halide perovskite films

“…Radicchi et al have investigated the chemistry of typical precursor solutions employed for lead halide perovskite synthesis by a combined experimental and computational approach. 20 Many groups have studied the effect of humidity and oxygen on the perovskites. [20][21][22] Hao Xiong et al have studied solvent vapour annealing of oriented PbI 2 lms for improved crystallization of perovskite lms in the air.…”

“…20 Many groups have studied the effect of humidity and oxygen on the perovskites. [20][21][22] Hao Xiong et al have studied solvent vapour annealing of oriented PbI 2 lms for improved crystallization of perovskite lms in the air. 23 Jun Luo et al studied the mechanism and effect of g-butyrolactone solvent vapour post-annealing on the perovskite of a mesoporous solar cell structure.…”