Structural and thermodynamic limits of layer thickness in 2D halide perovskites

Chan Myae Myae Soe, G. P. Nagabhushana, Radha Shivaramaiah, Hsinhan Tsai, Wanyi Nie, Jean Christophe Blancon, Ferdinand Melkonyan, Duyen H. Cao, Boubacar Traoré, Laurent Pedesseau, Mikaël Kepenekian, Claudine Katan, Jacky Even, Tobin J. Marks, Alexandra Navrotsky, Aditya D. Mohite, Constantinos C. Stoumpos, Mercouri G. Kanatzidis

Research output: Contribution to journalArticlepeer-review

165 Scopus citations


In the fast-evolving field of halide perovskite semiconductors, the 2D perovskites (A′)2(A)n1MnX3n+1 [where A = Cs+, CH3NH3+, HC(NH2)2+; A′ = ammonium cation acting as spacer; M = Ge2+, Sn2+, Pb2+; and X = Cl, Br, I] have recently made a critical entry. The n value defines the thickness of the 2D layers, which controls the optical and electronic properties. The 2D perovskites have demonstrated preliminary optoelectronic device lifetime superior to their 3D counterparts. They have also attracted fundamental interest as solution-processed quantum wells with structural and physical properties tunable via chemical composition, notably by the n value defining the perovskite layer thickness. The higher members (n > 5) have not been documented, and there are important scientific questions underlying fundamental limits for n. To develop and utilize these materials in technology, it is imperative to understand their thermodynamic stability, fundamental synthetic limitations, and the derived structure–function relationships. We report the effective synthesis of the highest iodide n-members yet, namely (CH3(CH2)2NH3)2(CH3NH3)5Pb6I19 (n = 6) and (CH3(CH2)2NH3)2(CH3NH3)6Pb7I22 (n = 7), and confirm the crystal structure with single-crystal X-ray diffraction, and provide indirect evidence for “(CH3(CH2)2NH3)2(CH3NH3)8Pb9I28” (“n = 9”). Direct HCl solution calorimetric measurements show the compounds with n > 7 have unfavorable enthalpies of formation (ΔHf), suggesting the formation of higher homologs to be challenging. Finally, we report preliminary n-dependent solar cell efficiency in the range of 9–12.6% in these higher n-members, highlighting the strong promise of these materials for high-performance devices.

Original languageEnglish (US)
Pages (from-to)58-66
Number of pages9
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number1
StatePublished - Jan 2 2019
Externally publishedYes


  • Formation enthalpy
  • Homologous series
  • Layered compounds
  • Perovskites
  • Photovoltaics
  • Ruddlesden–Popper halide

ASJC Scopus subject areas

  • General


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