Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 116, Issue 1, Pages 58-66Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1811006115
Keywords
layered compounds; homologous series; Ruddlesden-Popper halide perovskites; formation enthalpy; photovoltaics
Categories
Funding
- Office of Naval Research [N00014-17-1-2231]
- Center for Light Energy Activated Redox Processes (LEAP), an Energy Frontier Research Center - US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0001059]
- Department of Energy, Office of Basic Energy Sciences [08SPCE973]
- LANL Laboratory Directed Research and Development Program
- Agence Nationale pour la Recherche (TRANSHYPERO Project)
- Institut Universitaire de France
- US Department of Energy [DE-FG02-03ER46053]
- International Institute for Nanotechnology, Materials Research Science and Engineering Center (National Science Foundation Grant) [DMR-1121262]
- Keck Foundation
- State of Illinois
- Northwestern University
- US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]
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In the fast-evolving field of halide perovskite semiconductors, the 2D perovskites (A')(2)(A)(n-1)MnX3n+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)(2)NH3)(2)(CH3NH3)(5)Pb6I19 (n = 6) and (CH3(CH2)(2)NH3)(2)(CH3NH3)(6)Pb7I22 (n = 7), and confirm the crystal structure with single-crystal X-ray diffraction, and provide indirect evidence for (CH3(CH2)(2)NH3)(2)(CH3NH3)(8)Pb9I28 (n = 9). Direct HCl solution calorimetric measurements show the compounds with n > 7 have unfavorable enthalpies of formation (Delta H-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.
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