Preparation of Single-Phase Films of CH3NH3Pb(I1–x Br x )3 with Sharp Optical Band Edges

• Published in: The journal of physical chemistry letters Vol. 5; no. 15; pp. 2501 - 2505
• Main Authors: Sadhanala, Aditya, Deschler, Felix, Thomas, Tudor H, Dutton, Siân E, Goedel, Karl C, Hanusch, Fabian C, Lai, May L, Steiner, Ullrich, Bein, Thomas, Docampo, Pablo, Cahen, David, Friend, Richard H
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 07.08.2014
• Subjects: Energy Conversion and Storage; Energy and Charge Transport; iodide-bromide perovskite; organometallic lead halide perovskite; Urbach energy; PDS
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/jz501332v

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(I1–x Br x )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 CH3NH3PbI1.2Br1.8. We demonstrate a bromide–iodide lead perovskite film (CH3NH3PbI1.2Br1.8) with an optical bandgap of 1.94 eV, which is optimal for tandem cells of these materials with crystalline silicon devices.