Symmetrization of the Crystal Lattice of MAPbI₃ Boosts the Performance and Stability of Metal-Perovskite Photodiodes.

Abstract

Semiconducting lead triiodide perovskites (APbI₃ ) have shown remarkable performance in applications including photovoltaics and electroluminescence. Despite many theoretical possibilities for A⁺ in APbI₃ , the current experimental knowledge is largely limited to two of these materials: methylammonium (MA⁺ ) and formamidinium (FA⁺ ) lead triiodides, neither of which adopts the ideal, cubic perovskite structure at room temperature. Here, a volume-based criterion is proposed for cubic APbI₃ to be stable, and two perovskite materials MA_1-_x EA_x PbI₃ (MEPI, EA⁺ = ethylammonium) and MA_1-_y DMA_y PbI₃ (MDPI, DMA⁺ = dimethylammonium) are introduced. Powder and single-crystal X-ray diffraction (XRD) results reveal that MEPI and MDPI are solid solutions possessing the cubic perovskite structure, and the EA⁺ and DMA⁺ cations play similar roles in the symmetrization of the crystal lattice of MAPbI₃ . Single crystals of MEPI and MDPI are grown and made into plates of a range of thicknesses, and then into metal-perovskite photodiodes. These devices exhibit tripled diffusion lengths and about tenfold enhancement in stability against moisture, both relative to the current benchmark MAPbI₃ . In this study, the systematic approach to materials design and device fabrication greatly expands the candidate pool of perovskite semiconductors, and paves the way for high-performance, single-crystal perovskite devices including solar cells and light emitters.