The intrinsic properties of FA_(1-:X)MA_xPbI₃ perovskite single crystals

Organic-inorganic hybrid perovskites with mixed organic cations and/or halides have attracted increasing attention due to their superior optoelectronic properties, which are tailorable for different applications. To obtain a deeper understanding of materials properties, single crystals are regarded as the best platform among various building blocks for fundamental study. Here, we synthesized a series of perovskite single crystals with mixed organic cations (APbI₃, A = CH₃NH₃⁺, MA⁺; or CH(NH₂)₂⁺, FA⁺) along the compositional space, and conducted a systematic investigation to correlate the carrier behavior with the organic cations. The single crystals were synthesized via inverse temperature crystallization assisted by hydroiodic acid, where the quality of the crystals could be judiciously controlled by the thermodynamic process. It is found that the substitution of 15% MA⁺ in FAPbI₃ single crystals stabilizes the phase with the best charge transport characteristics. Both photodetector and J-V measurements suggested that FA_0.85MA_0.15PbI₃ single crystal exhibits suppressed ion migration compared with the counterpart FA_0.15MA_0.85PbI₃ single crystal. These results represent an important step to highlight the role of organic cations in hybrid perovskite materials, which will further benefit fundamental understanding of materials and device optimization.