Influence of Annealing and Composition on the Crystal Structure of Mixed-Halide, Ruddlesden-Popper Perovskites

Journal Article (Journal Article)

Mixed-halide two-dimensional (2D) hybrid organic-inorganic perovskites offer an important opportunity to control the band gap for applications in optoelectronic devices. This study focuses on phenethylammonium lead halide [(PEA)2Pb(I1-xBrx)4] films, the pure iodide form of which is one of the most widely studied optically active 2D perovskite systems. Resonant infrared, matrix-assisted pulsed laser evaporation is used to grow films to explore the effects of post-growth annealing and mixed-halide composition. The composition, crystal structure, and optical properties are studied for as-grown and annealed films of (PEA)2Pb(I1-xBrx)4 for x = 0, 0.25, 0.5, 0.75, and 1. First-principles calculations are used in conjunction with the experimental data to explain the mixed-halide behavior that does not trend monotonically with the bromide content. Important results of this work are as follows: (i) X-ray diffraction reveals evidence for halide phase separation around x = 0.25, consistent with first-principles calculations, whereas no phase separation is observed for x = 0.5 and above and (ii) a unique photoluminescence (PL) peak splitting is observed for x = 0.75, a composition for which no compositional phase separation is observed. The PL splitting is tentatively explained by the coexistence of two distinct types of halide short-range ordering at x = 0.75. Overall, this study demonstrates that mixed-halide n = 1 Ruddlesden-Popper perovskites are not simple random alloys but that instead, they display distinct sites and ordering preferences of the different halide anions. These preferences are critical to understand and rationally tune the properties of the materials.

Full Text

Duke Authors

Cited Authors

  • Wright, NE; Qin, X; Xu, J; Kelly, LL; Harvey, SP; Toney, MF; Blum, V; Stiff-Roberts, AD

Published Date

  • April 12, 2022

Published In

Volume / Issue

  • 34 / 7

Start / End Page

  • 3109 - 3122

Electronic International Standard Serial Number (EISSN)

  • 1520-5002

International Standard Serial Number (ISSN)

  • 0897-4756

Digital Object Identifier (DOI)

  • 10.1021/acs.chemmater.1c04213

Citation Source

  • Scopus