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

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 116; no. 1; pp. 58 - 66
• Main Authors: Soe, Chan Myae Myae, Nagabhushana, G. P., Shivaramaiah, Radha, Tsai, Hsinhan, Nie, Wanyi, Blancon, Jean-Christophe, Melkonyan, Ferdinand, Cao, Duyen H., Traoré, Boubacar, Pedesseau, Laurent, Kepenekian, Mikaël, Katan, Claudine, Even, Jacky, Marks, Tobin J., Navrotsky, Alexandra, Mohitee, Aditya D., Stoumpos, Constantinos C., Kanatzidis, Mercouri G.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 02.01.2019
• Series: PNAS Plus
• Subjects: Ammonium; bio-inspired; catalysis (heterogeneous); catalysis (homogeneous); charge transport; Chemical composition; Chemical Sciences; Condensed Matter; Cristallography; Crystal structure; Electronics industry; Energy Sciences; Enthalpy; Homology; hydrogen and fuel cells; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Iodides; Lead; magnetism and spin physics; Material chemistry; Material Science; materials and chemistry by design; Materials Science; mesostructured materials; Optical properties; optics; Optoelectronic devices; or physical chemistry; Organic chemistry; Perovskite; Perovskites; phonons; photosynthesis (natural and artificial); Photovoltaic cells; Physical properties; Physical Sciences; Physics; PNAS Plus; Quantum wells; Semiconductors; Service life assessment; Single crystals; solar (fuels); solar (photovoltaic); Solar cells; Structure-function relationships; synthesis (novel materials); synthesis (scalable processing); synthesis (self-assembly); Theoretical and; Thermodynamics; Thickness; X-ray diffraction; formation enthalpy; layered compounds; Ruddlesden–Popper halide perovskites; homologous series; photovoltaics; calorimetry; Layered compounds; Ruddlesden-Popper halide perovskites; quantum confinement; light emitting diodes
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1811006115

In the fast-evolving field of halide perovskite semiconductors, the 2D perovskites (A′)₂(A)n−1M n X3n+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 (ΔH f), 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.