Hidden polymorphism of FAPbI3 discovered by Raman spectroscopy. Issue 15 (12th April 2021)

• Record Type: Journal Article
• Authors: Ibaceta-Jaña, Josefa; Muydinov, Ruslan; Rosado, Pamela; Vinoth Kumar, Sri Hari Bharath; Gunder, Rene; Hoffmann, Axel; Szyszka, Bernd; Wagner, Markus R.
• Is Part Of: Physical chemistry chemical physics. Volume 23:Issue 15(2021)
• Page Start: 9476
• Page End: 9482
• Publication Date: 2021-04-12
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d1cp00102g
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Formamidinium lead iodide (FAPbI3 ) can exhibit polymorphism at ambient conductions. Three different structural configurations and their thermally activated phase transitions are identified by temperature dependent micro-Raman spectroscopy. Abstract : Formamidinium lead iodide (FAPbI3 ) can be used in its cubic, black form as a light absorber material in single-junction solar cells. It has a band-gap (1.5 eV) close to the maximum of the Shockley–Queisser limit, and reveals a high absorption coefficient. Its high thermal stability up to 320 °C has also a downside, which is the instability of the photo-active form at room temperature (RT). Thus, the black α-phase transforms at RT with time into a yellow non-photo-active δ-phase. The black phase can be recovered by annealing of the yellow state. In this work, a polymorphism of the α-phase at room temperature was found: as-synthesized (αi ), degraded (αδ ) and thermally recovered (αrec ). They differ in the Raman spectra and PL signal, but not in the XRD patterns. Using temperature-dependent Raman spectroscopy, we identified a structural change in the αi -polymorph at ca. 110 °C. Above 110 °C, the FAPbI3 structure has undoubtedly cubic Pm 3̄ m symmetry (high-temperature phase: αHT ). Below that temperature, the αi -phase was suggested to have a distorted perovskite structure with Im 3̄ symmetry. Thermally recovered FAPbI3 (αrec ) also demonstrated the structural transition to αHT at the same temperature ( ca. 110 °C) during its heating. The understanding of hybrid perovskites may bring additional assets in the development of new and stable structures.