Applications brief: Chloride incorporation process in CH3NH3PbI3-xClx perovskites via nanoscale bandgap maps

Key results


  • CH3NH3PbI3-xClx perovskites enable the creation of highly efficient solar cells
  • PTIR was used in this study to measure the bandgap of CH3NH3PbI3-xClx films and determine local chloride content
  • Despite small chloride content, CH3NH3PbI3-xClx films showed better thermal stability than CH3NH3PbI3 films fabricated by the same method

Key words

mixed-halide organolead perovskites | PTIR | bandgap | nanoscale mapping | solar cells

Authors

J. Chae, Q. Dong, J. Huang, A. Centrone

Abstract

CH3NH3PbI3-xClx 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 (PTIR), an in situ technique with nanoscale resolution, is leveraged to measure the bandgap of CH3NH3PbI3-xClx 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 homogenous Cl-poorer (x < 0.06) phase, suggesting that methylammonium-chrloride is progressively expelled from the film.Despite the small chloride content, CH3NH3PbI3-xClx films show better thermal stability up to 140 °C with respect CH3NH3PbI3 films fabricated with the same methodology.


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PTIR image ratios close to the absorption band gap in MAPbI3-xClx mirroring the Cl- distribution. The above images show PTIR absorption ratio maps recorded by illuminating the sample at 702 nm (a), at 678 nm (b) and at 645 nm (c).
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