A strategy for phase-selective growth of FAPbI3 single crystals across a wide temperature range

The feature of metastable α -phase for FAPbI 3 at room temperature results in a relatively high growth temperature required for a pure α -phase FAPbI 3 single crystal. Here, we demonstrate a general strategy to selectively control the α - and δ -phase formation of FAPbI 3 single crystals over a wide temperature range (from 70 to 110 ℃) via inverse temperature crystallization. Phase selection is governed by solution saturation and seed type, while the introduction of formic acid can further lower the crystallization temperature without affecting this seed-mediated control. For improved stability during characterization, most structural and optoelectronic measurements were performed on FA 0.93 Cs 0.07 PbI 3 single crystals, while control experiments on undoped FAPbI 3 showed the same overall phase-selection trend. The resulting α -phase crystals exhibit good crystallinity (XRC FWHM = 0.041°) and long average carrier lifetimes (∼10 μs), demonstrating that the proposed strategy enables stable phase-selective growth and low-temperature single-crystal growth in the present system.