Understanding the "Molten Salt" Synthesis of MAPbI3 – Characterization of New Lead(II)‐Ammine Complexes as Intermediates. Issue 15 (7th March 2021)

• Record Type: Journal Article
• Authors: Daub, Michael; Hillebrecht, Harald
• Is Part Of: European journal of inorganic chemistry. Issue 15(2021)
• Page Start: 1490
• Page End: 1497
• Publication Date: 2021-03-07
• Subjects: Coordination compounds -- Isolated intermediates -- Lead -- Methylamine ligands -- Precursors -- Structure elucidation; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.202100077
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract: The so‐called "molten salt process" is used to enhance the properties of perovskite‐based solar cells using CH3 NH3 PbI3 (MAPbI3 ) as an absorber. We have characterized intermediates of the reaction of CH3 NH2 with both PbI2 and MAPbI3 . The reaction of PbI2 or MAPbI3 in liquid CH3 NH2 yields white [Pb(CH3 NH2 )6 ]I2 (cubic K2 PtCl6 type), representing a typical coordination compound and the first homoleptic ammine Pb(II)‐complex. Reducing the CH3 NH2 vapor pressure and/or increasing the temperature gives pale‐yellow platelets of the neutral complex Pb(CH3 NH2 )4 I. The coordination of Pb 2+ consists of four neutral CH3 NH2 ligands and two iodide anions with quite different distances, so the complex could also be written as [Pb(CH3 NH2 )4 I] + I − . Traces of humidity in the molten salt process result in the formation of Pb(OH)I and a new compound, namely (CH3 NH3 )5 (CH3 NH2 )2 Pb2 I9 with isolated [Pb2 I9 ] 5− di‐octahedra. Charge compensation takes place by CH3 NH3 + cations and novel dimers [CH3 NH3 ⋅⋅⋅NH2 CH3 ] +, where a cation and neutral molecule are connected via a N−H⋅⋅⋅N hydrogen bond. Abstract : Two intermediates, [Pb(CH3 NH2 )6 ]I2 and Pb(CH3 NH2 )4 I2, were isolated from the reaction of gaseous CH3 NH2 with black MAPbI3, where CH3 NH2 acts as a sigma donor ligand to Pb 2+ . The release of CH3 NH2 yields pristine MAPbI3 and PbI2, respectively. Traces of water during this "molten salt approach" reveal Pb(OH)I and the new compound (CH3 NH3 )5 (CH3 NH2 )2 Pb2 I9 as byproducts. These reactions are important for understanding defect healing in MAPbI3 absorber materials in perovskite solar cells.