Preparation of single-phase films of CH3NH3Pb(I 1- xBrx)3 with sharp optical band edges

Aditya Sadhanala, Felix Deschler, Tudor H. Thomas, Siân E. Dutton, Karl C. Goedel, Fabian C. Hanusch, May L. Lai, Ullrich Steiner, Thomas Bein, Pablo Docampo, David Cahen, Richard H. Friend

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378 Scopus citations


Organometallic lead-halide perovskite-based solar cells now approach 18% efficiency. Introducing a mixture of bromide and iodide in the halide composition allows tuning of the optical bandgap. We prepare mixed bromide-iodide lead perovskite films CH3NH3Pb(I 1-xBrx)3 (0 ≤ x ≤ 1) by spin-coating from solution and obtain films with monotonically varying bandgaps across the full composition range. Photothermal deflection spectroscopy, photoluminescence, and X-ray diffraction show that following suitable fabrication protocols these mixed lead-halide perovskite films form a single phase. The optical absorption edge of the pure triiodide and tribromide perovskites is sharp with Urbach energies of 15 and 23 meV, respectively, and reaches a maximum of 90 meV for CH 3NH3PbI1.2Br1.8. We demonstrate a bromide-iodide lead perovskite film (CH3NH3PbI 1.2Br1.8) with an optical bandgap of 1.94 eV, which is optimal for tandem cells of these materials with crystalline silicon devices.

Original languageEnglish
Pages (from-to)2501-2505
Number of pages5
JournalJournal of Physical Chemistry Letters
Issue number15
StatePublished - 7 Aug 2014
Externally publishedYes


  • PDS
  • Urbach energy
  • iodide-bromide perovskite
  • organometallic lead halide perovskite


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