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Nano Lett. 2015 Dec 9;15(12):8114-21. doi: 10.1021/acs.nanolett.5b03556. Epub 2015 Nov 5.

Chloride Incorporation Process in CH₃NH₃PbI(3-x)Cl(x) Perovskites via Nanoscale Bandgap Maps.

Author information

1
Center for Nanoscale Science and Technology, National Institute of Standards and Technology , 100 Bureau Drive, Gaithersburg, Maryland 20899, United States.
2
Maryland Nanocenter, University of Maryland , College Park, Maryland 20742 United States.
3
Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0656, United States.

Abstract

CH3NH3PbI(3-x)Cl(x) perovskites enable fabrication of highly efficient solar cells. Chloride ions benefit the morphology, carrier diffusion length, and stability of perovskite films; however, whether those benefits stem from the presence of Cl(-) in the precursor solution or from their incorporation in annealed films is debated. In this work, the photothermal-induced resonance, an in situ technique with nanoscale resolution, is leveraged to measure the bandgap of CH3NH3PbI(3-x)Cl(x) films obtained by a multicycle coating process that produces high efficiency (∼16%) solar cells. Because chloride ions modify the perovskite lattice, thereby widening the bandgap, measuring the bandgap locally yields the local chloride content. After a mild annealing (60 min, 60 °C) the films consist of Cl-rich (x < 0.3) and Cl-poor phases that upon further annealing (110 °C) evolve into a homogeneous Cl-poorer (x < 0.06) phase, suggesting that methylammonium-chrloride is progressively expelled from the film. Despite the small chloride content, CH3NH3PbI(3-x)Cl(x) films show better thermal stability up to 140 °C with respect CH3NH3PbI3 films fabricated with the same methodology.

KEYWORDS:

Mixed-halide organolead perovskites; PTIR; bandgap; nanoscale mapping; solar cells

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