Precipitation of CH₃NH₃PbCl₃ in\nCH₃NH₃PbI₃ and Its Impact on Modulated\nCharge Separation

Abstract

A precipitation\nof CH₃NH₃PbCl₃ (MAPbCl₃) in CH₃NH₃PbI₃ (MAPbI₃) has been observed for deposition from solutions containing CH₃NH₃I (MAI), PbCl₂ and small amounts\nof ammoniumvaleric acid iodide (HOOC­(CH₂)₄NH₃I or AVAI) in <i><i>N</i></i>,<i><i>N</i></i>-dimethylformamide. The influence of the\nprecipitation of MAPbCl₃ on the electronic properties of\nthe free perovskite layer and of the nanoporous TiO₂/perovskite\nnanocomposite has been investigated by modulated surface photovoltage\nspectroscopy. The lowest characteristic energy of exponentially distributed\ndefect states below the band gap was found for the highest amount\nof AVAI in the solution (2.6% for the given experiments). Stabilization\nof MACl by AVA and the role of coadsorption of ions on TiO₂ surfaces for charge separation and layer formation are discussed\non the basis of interaction and adsorption energies obtained by molecular\nmodeling.