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The understanding and tailoring of crystalline defects have been important factors in the technological deployment of established semiconductors. Here, we report the secondary phase (SP) defects of CsPb2Br5 in CsPbBr3 crystals grown by inverse temperature crystallization. The micron-scale SP defects are found to possess a well-defined polyhedral morphology, illustrated by the 14-hedron model. A heterogeneous nucleation mechanism of SP defects on the step-like surface of CsPbBr3 associated with the deviation of the chemical state of the precursor solution is proposed. The spatial inhomogeneity distribution of SP defects is highlighted along the CsPbBr3 crystal growth direction. The SP defects area density at the subsurface is about 6.3%, but it exponentially decreases to 0.51% after thinning for 0.2 mm. Correspondingly, the hole mobility increases from 41.79 to 74.54 cm−2 V−1 s−1. Moreover the infrared transmittance, bulk resistivity and photoresponse ON/OFF ratio are significantly elevated. We emphasize that the lattice distortion region in the near-surface induced by the high density of SP defects severely deteriorates carrier transport due to the formed trapping centers, interface transport barrier and intrinsically poor transmission along the c axis. Therefore, understanding and eliminating SP defects is a preferred alternative for achieving high-performance CsPbBr3-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) organic–inorganic hybrid halide perovskites have recently attracted extensive attention for electronic and optoelectronic applications due to their tunable properties and superior stability compared with their three-dimensional (3D) counterparts. Here, we report two kinds of organic cation (linear butylamine (BA) and branched isobutylamine (i-BA)) tailored CsPbBr3 crystals, namely (BA)2CsPb2Br7 and (i-BA)2CsPb2Br7, grown by the temperature-cooling method. The organic cations' adjustable anisotropic structure, optoelectronic properties and X-ray detection performance have been systematically investigated. By shortening the spacer cation from BA to i-BA, the degree of anisotropy in 2D perovskite crystals is decreased, which may be ascribed to the reduced interlayer distance and barrier height resulting from the enhanced electronic coupling between neighboring organic cations. In particular, the device based on the (BA)2CsPb2Br7 crystal along the ab plane exhibits superior X-ray sensitivity up to 13.26 mC Gy−1 cm−2 at a relatively low electric field of 2.53 V mm−1, owing to the multiple quantum well structure that restricts the charge carrier transport within the ab plane resulting in efficient charge collection. Simultaneously, a superior long-term working stability is obtained under a high X-ray dose rate of 278.4 μGy s−1. We anticipate that these findings will be helpful for the development of Ruddlesden–Popper perovskites for future research and applications. [ABSTRACT FROM AUTHOR]

The "self-trap state" in low demensional halide perovskites usually induces highly efficient below-gap broadband luminescence, which makes them promising fluorescence emitting materials. However, the luminescence mechanism based on the "self-trap state" is not well understood as yet. In this work, solution-grown quasi-one-dimensional RbPbI3 crystals reveal a large Stokes shift of ∼0.57 eV, wide and strong luminescence, and a linear power-dependent luminescence, whose luminescence mechanism was attributed to the formation of a "self-trap state" in RbPbI3. Furthermore, Cs substitutional counterpart (RbxCs1−x)PbI3 crystals were found to adjust the distortions of the PbI6 octahedron and the self-trap-state-induced luminescence properties. Our work provides a new strategy to control the "self-trap-state"-induced luminescence in low demensional halide perovskite materials. [ABSTRACT FROM AUTHOR]

Herein, we report the details of the synthesis and crystal growth of a lead-free perovskite derivative Cs2TeI6 crystal, which reveals long-term environmental stability. The synthesis process is optimized to obtain pure Cs2TeI6 polycrystals, and to eliminate the formation of residual CsI resulting from high vapor pressure. Subsequently, the Cs2TeI6 single crystal with dimensions of Φ10 mm × 55 mm is grown by the vertical Bridgman method. The as-grown 0-D structural Cs2TeI6 crystal exhibits a high resistivity of 9.92 × 1011 Ω cm, and resulting mobilities of 4.03 ± 0.33 cm2 V−1 s−1 and 9.40 ± 0.45 cm2 V−1 s−1 for electrons and holes, respectively. The Au/Cs2TeI6/Au device shows a good response for optoelectronic and X-ray detection, with a relatively high X-ray sensitivity of 27.8 μC Gy−1 cm−2 and a low detection limit of 72.5 nGy s−1. [ABSTRACT FROM AUTHOR]

Ion migration in halide perovskite materials usually brings an intractable problem in the working stability of solar cells and photoelectrical detectors. The mechanism of ion migration and its impact on physical properties are still open questions. In this work, the ion migration behavior in solution-grown CsPbBr3 crystals was observed by the hysteresis in current–voltage curves and the temperature dependent reversed current–time measurements. Defect proliferation phenomena (new defects of [VCs]− and [PbBr]2+) originating from ion migration were verified by thermally stimulated current spectroscopy. Our results also give evidence that Cs+ ions also participate in the process of ion migration except the widely considered Br− ions. Furthermore, the photoelectric properties of the CsPbBr3 device were found to be seriously deteriorated after the ion migration. Our work demonstrates the strong correlation between the ion migration and physical properties in halide perovskites. [ABSTRACT FROM AUTHOR]

X-ray detection is of great significance for medical diagnostics, industrial non-destructive inspection, nuclear plants and scientific research. However, high sensitivity is needed for X-ray detectors to reduce the radiation dose applied to human bodies for the applications of medical imaging and security checks. Here, we reported sensitive X-ray detectors made of solution-grown inorganic lead perovskite CsPbBr3 single crystals and the synthesis of high-quality inorganic lead perovskite CsPbBr3 single crystals using an improved low temperature solution method, which exhibited high transmittance, mobility and mobility–lifetime products. By designing the detector in an asymmetric electrode configuration, ion migration was effectively suppressed under a high voltage with a low dark current and an outstanding photoresponse. The optimized detector exhibited high sensitivity of 1256 μC Gy−1 cm−2 for 80 kVp X-ray detection under a relatively low electric field of 20 V mm−1, which was 60 times higher than that of commercially used α-Se detectors. Due to its facile synthesis, low cost, long-term stability, and high detection sensitivity, CsPbBr3 is expected to be an outstanding candidate for commercialized sensitive X-ray detectors. [ABSTRACT FROM AUTHOR]

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.