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Hot-Paper Hillebrecht in CHEMISTRY: Perovskites

Tailoring the Band Gap in 3D Hybrid Perovskites by Substitution of the Organic Cations

Abstract: Tuning the optical properties of MAPbI3 (MA=methylammonium) is a key requirement to increase the efficiency of perovskite solar cells (PSCs). Simple precipitation from solution allows the partial substitution of MA in MAPbI3 by H3NCH2CH2NH3 (H2en). Surprisingly, there is 1:1 exchange of the monovalent cation MA by the dication H2en. The charge compensation results from a deficit of Pb2+, leading to a series MA1@2y(H2en)2yPb1@yI3 with 0,y0.25. This model has been supported by single-crystal measurements and NMR investigations. The substitution results in a continuous shift of the band gap from 1.51 to 2.1 eV and a color change from black to orange-red. The H2en content stabilizes the cubic high-temperature (HT) form of MAPbI3. There is a linear correlation between band gap and unit cell volume. The substitution enables controlled band gap tuning because the extent of substitution is closely related to the applied MA:H2en ratio in solution.

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DOI: 10.1002/chem.201800244