Iodide vs Chloride: The Impact of Different Lead Halides on the Solution Chemistry of Perovskite Precursors

Abstract

Controlled perovskite growth from solution is crucial for efficient optoelectronic applications and requires a deep understanding of the perovskite precursor chemistry. The so-called “chlorine route” to lead–iodide perovskite, using PbCl2 or MACl additive as a precursor, is frequently employed to form homogeneous perovskite layers by retarding perovskite crystallization. To understand the role of chlorine-containing lead precursors in solution, we analyze the chemical interaction of PbCl2 and PbI2 precursors with commonly employed solvents (γ-butyrolactone (GBL), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO)) by combining first-principles simulations and experimental UV–vis spectroscopy in diluted precursor solutions. Ab initio molecular dynamics simulations reveal reduced solvation and an increased free energy barrier of lead-halide bond dissociation of PbCl2 compared to PbI2 with chlorine acting as a stronger ligand, which, in turn, limits the solvent coordination. In contrast to PbI2, PbCl2 absorption spectra lack signatures of high-valent [PbCl n ]2–n complexes and show low sensitivity on the employed solvent, as confirmed by combined UV–vis and excited-state time-dependent density functional theory (TD-DFT) analysis. Altogether, our data suggest the presence of residual chlorine coordinated to Pb even in the presence of high iodine excess, which may retard the perovskite growth and could also lead to chlorine incorporation within the lead–iodide perovskite crystal.

Challenges, Opportunities, and Prospects in Metal Halide Perovskites from Theoretical and Machine Learning Perspectives

“…[ 5 ] Cl and I showed different solvation interactions with solvents according to first‐principles simulations. [ 111 ]…”

“…However, recent studies show that solvents have a significant influence over MHPs film formation and oxidation. [5,30,111,112] For instance, in an Snbased halide perovskite whose PCE is now 14.6 %, [113] a hidden role of DMSO solvent was revealed that DMSO facilitates the oxidation of Sn 2 + to Sn 4 + , [30] which deteriorates solar cell performances. This study provides a valuable insight into that the solvent effects are directly related to the film formation and stability.…”

Investigation of the Solution Chemistry of Hybrid Organic–Inorganic Indium Halides for New Material Discovery

“…Despite the simplicity of these synthetic methods, there has been a myriad of other reported synthesis methods, ,− for example, using other solvents and various additives, which altogether suggest that much of this work has been done without an in-depth understanding of the impacts of solvents, solvent–solute interactions, and various additives. Recently, several computational studies have attempted to characterize metal halide precursor solutions with a particular focus on lead halide perovskites. − Investigations and understanding of the precursor solution chemistry are expected to result in optimized syntheses of high-quality lead halide perovskites.…”

Prospects for Tin-Containing Halide Perovskite Photovoltaics

“…Absorption spectroscopy on Pb solutions has revealed more highly coordinating solvents inhibit the formation of higher valency solvated polyiodide plumbates (PbI m 2– m + ) . These may exist as isolated complexes, as bridged chains, or within the colloidal species. , Moving to strongly coordinating halide ligands (Cl – > Br – > I – ), the absorption from more highly valent polyhalide plumbates is reduced . As there are few reports presenting absorption spectra of Sn perovskite solutions, and most being only SnI 2 , ,, the effect of solvents and halides on halogenostannate complexes (SnX m 2– m + ) in solution is yet to be understood, although undoubtedly impacts the crystallization.…”