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A Combined Theoretical and Experimental Study of CH3NH3PbI3 Containing AVAI Films Prepared via an Intramolecular Exchange Process C

Prajongtat, Pongthep, Hannongbua, Supa
Journal of physical chemistry 2018 v.122 no.34 pp. 19705-19711
X-ray diffraction, density functional theory, dimethyl sulfoxide, electrostatic interactions, iodides, organoiodine compounds, physical chemistry, scanning electron microscopy, solar cells, spectroscopy, valeric acid
Methylammonium lead iodide (CH₃NH₃PbI₃) has emerged as a superior light-absorbing material for perovskite solar cells, mainly because of its excellent optical and electronic properties. However, insufficient long-term stability of CH₃NH₃PbI₃ has severely hindered its practical applications. The direct addition of 5-ammonium valeric acid iodide (HOOC(CH₂)₄NH₃I or AVAI) to perovskite precursors, such as CH₃NH₃I and PbI₂, was found to improve the stability of CH₃NH₃PbI₃, but can limit the incorporation of AVA⁺ into the CH₃NH₃PbI₃ structure because of strong competitive interactions between AVA⁺ and CH₃NH₃⁺ with PbI₂ through the same electrostatic interactions. Here, we present an alternative approach to prepare high-quality CH₃NH₃PbI₃ containing AVAI films via an intramolecular exchange process. The films were prepared from precursor complexes, that is, organic lead iodide complexes, by the intramolecular exchange of dimethyl sulfoxide intercalated in the complexes with CH₃NH₃⁺. Scanning electron microscopy, grazing-incidence X-ray diffraction, and modulated surface photovoltage spectroscopy were employed to characterize morphological and electronic properties of the prepared materials. To gain a deeper understanding of the formation and stability of organic lead iodide complexes and perovskite, the structures, binding strength, and formation energies of these materials were investigated by density functional theory calculations.