Reversible Halide Exchange Reaction of Organometal Trihalide Perovskite Colloidal Nanocrystals for Full-Range Band Gap Tuning

• Published in: Nano letters Vol. 15; no. 8; pp. 5191 - 5199
• Main Authors: Jang, Dong Myung, Park, Kidong, Kim, Duk Hwan, Park, Jeunghee, Shojaei, Fazel, Kang, Hong Seok, Ahn, Jae-Pyung, Lee, Jong Woon, Song, Jae Kyu
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 12.08.2015
• Subjects: Computational efficiency; Computing time; Exchange; Halides; Nanocrystals; Perovskites; Synthesis (chemistry); Tuning; Perovskite; composition tuning; photodetectors; anion exchange reaction; nanocrystals
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.5b01430

In recent years, methylammonium lead halide (MAPbX3, where X = Cl, Br, and I) perovskites have attracted tremendous interest caused by their outstanding photovoltaic performance. Mixed halides have been frequently used as the active layer of solar cells, as a result of their superior physical properties as compared to those of traditionally used pure iodide. Herein, we report a remarkable finding of reversible halide-exchange reactions of MAPbX3, which facilitates the synthesis of a series of mixed halide perovskites. We synthesized MAPbBr3 plate-type nanocrystals (NCs) as a starting material by a novel solution reaction using octylamine as the capping ligand. The synthesis of MAPbBr3–x Cl x and MAPbBr3–x I x NCs was achieved by the halide exchange reaction of MAPbBr3 with MACl and MAI, respectively, in an isopropyl alcohol solution, demonstrating full-range band gap tuning over a wide range (1.6–3 eV). Moreover, photodetectors were fabricated using these composition-tuned NCs; a strong correlation was observed between the photocurrent and photoluminescence decay time. Among the two mixed halide perovskite series, those with I-rich composition (x = 2), where a sole tetragonal phase exists without the incorporation of a cubic phase, exhibited the highest photoconversion efficiency. To understand the composition-dependent photoconversion efficiency, first-principles density-functional theory calculations were carried out, which predicted many plausible configurations for cubic and tetragonal phase mixed halides.