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Compared with the widely reported MAPbBr 3 single crystals, formamidinium-based (FA-based) hybrid perovskites FAPbBr 3 (FPB) with superior chemical and structure stability are expected to be more efficient and perform as more reliable radiation detectors at room temperature. Here, we employ an improved inverse temperature crystallization method to grow FPB bulk single crystals, where issues associated with the retrograde solubility behavior are resolved. A crystal growth phase diagram has been proposed, and accordingly, growth parameters are optimized to avoid the formation of NH 4 Pb 2 Br 5 secondary phase. The resulting FPB crystals exhibit a high resistivity of 2.8 × 10 9 Ω·cm and high electron and hole mobility-lifetime products (μτ) of 8.0 × 10 -4 and 1.1 × 10 -3 cm 2 ·V -1 , respectively. Simultaneously, the electron and hole mobilities (μ) are evaluated to be 22.2 and 66.1 cm 2 ·V -1 ·s -1 , respectively, based on the time-of-flight technique. Furthermore, a Au/FPB SC/Au detector is constructed that demonstrates a resolvable gamma peak from 59.5 keV 241 Am γ-rays at room temperature for the first time. An energy resolution of 40.1% is obtained at 30 V by collecting the hole signals. These results demonstrate the great potential of FAPbBr 3 as a hybrid material for γ-ray spectroscopy and imaging.

The metal halide perovskite CsPbBr 3 bulk crystals present electrical and optical performance discrepancy since the grown-in defects. Here, we first report the well-defined secondary phase (SP) particles of CsPb 2 Br 5 with polyhedral morphology in CsPbBr 3 crystals grown by the vertical Bridgman method. The resulting polyhedral morphology of CsPb 2 Br 5 particles associated with the trapping of PbBr 2 -rich droplets have been discussed on the basis of the "matrix-controlled" growth. Two morphological evolution paths are proposed, which result in a regular cube SP particle comprised by {100} facets for the final equilibrium. Furthermore, the wafer with superior optical transmittance exhibits a higher photoelectric response on-off ratio (∼2000) in contrast to ∼80 for the wafer with high density SP particles. The corresponding hole mobility (μ h ) is calculated with the values 289.99 and 26.91 cm -2 ·V -1 ·s -1 , respectively. The variation of μ h is attributed to the carrier transport trajectory affected by SP induced trapping defects and the weak combination.