Guodong Zhang

Abstract The relatively low resistivity and severe ion migration in CsPbBr 3 significantly degrade the performance of X‐ray detectors due to their high detection limit and current drift. The electrical properties and X‐ray detection performances of CsPbBr 3 −nIn single crystals are investigated by doping the iodine atoms into the melt‐grown CsPbBr 3 . The resistivity of CsPbBr 3 −nIn single crystals increases from 3.6 × 10 9 (CsPbBr 3 ) to 2.2 × 10 11 (CsPbBr 2 I) Ω cm, restraining the leak current and decreasing the detection limit of the detector. Additionally, CsPbBr 3 −nIn single crystals exhibit stable dark currents, arising from their high ion migration activation energy. A record sensitivity of 6.3 × 104 µC Gy −1 cm −2 (CsPbBr 2.9 I 0.1 ) and a low detection limit of 54 nGy s −1 (CsPbBr 2 I) are achieved by CsPbBr 3 −nIn single crystals for the 120 keV hard X‐ray detection under a 5000 V cm −1 electrical field. The CsPbBr 2.9 I 0.1 detector shows a stable current response with a dark current density of 0.58 µA cm −2 for 30 days and clear imaging for 120 keV Xrays at ambient conditions. The effective iodine atom doping strategy makes the CsPbBr 3 −nIn single crystals promising for reproducible high‐energy hard X‐ray imaging systems.

This work demonstrates a novel photovoltaic application in which graphdiyne (GD) can be employed as a host material in a perovskite active layer for the first time. In the device fabrication, the best molar ratio for active materials is verified as PbI2/MAI/GD being 1:1:0.25, yielding a peak power-conversion efficiency of 21.01%. We find that graphdiyne, as the host material, exerts significant influence on the crystallization, film morphology, and a series of optoelectronic properties of the perovskite active layer. A uniform MAPbI3 film with highly crystalline qualities, large domain sizes, and few grain boundaries was realized with the introduction of graphdiyne. Moreover, the current–voltage hysteresis was negligible, and device stability was significantly improved as well. The results indicate that graphdiyne as the host active material presents great potential for the enhancement of the performance of perovskite solar cells.

All-inorganic perovskite CsPbBr3 has been considered as one of the star semiconductors due to its inspiring optoelectronic properties and higher stability than the organic–inorganic hybrid counterparts. The preparation of large-size single crystals with low trap density and the performance optimization on the devices still challenge the commercial application of this material. Here the large transparent CsPbBr3 single crystal (ϕ 24 mm × 90 mm) was grown by a modified Bridgman method. With the determination of crystallographic directions, the anisotropic optoelectronic properties were investigated for the first time. The result shows a high electron mobility (11.61 cm2/(V s)) along the b axis, one order of magnitude higher than that along the c axis. Moreover, the photoresponse measurement yields a high responsivity (5.83 A/W) and external quantum efficiency (1360%) on the (001) plane irradiated by the 532 nm laser diode with 1 mW/cm2 under 10 V bias, which is a 305% enhancement compared with the (010) plane. Our study on anisotropic optoelectronic properties of CsPbBr3 will provide a significant approach to enhance the performance of single-crystalline devices.

The hybrid perovskites with special optoelectronic properties have attracted more attention to the scientific and industrial applications. However, because of the toxicity and instability of lead complexes, there is interest in finding a nontoxic substitute for the lead in the halides perovskites and solving the ambiguous crystal structures and phase transition of NH(CH3)3SnX3 (X = Cl, Br). Here, we report the bulk crystal growths and different crystal morphologies of orthorhombic hybrid perovskites NH(CH3)3SnX3 (X = Cl, Br) in an ambient atmosphere by bottom-seeded solution growth (BSSG) method. More importantly, detailed structural determination and refinements, phase transition, band gap, band structure calculations, nonlinear optical (NLO) properties, XPS, thermal properties, and stability of NH(CH3)3SnX3 (X = Cl, Br) single crystals are demonstrated. NH(CH3)3SnCl3 single crystal undergoes reversible structural transformation from orthorhombic space group Cmc21 (no. 36) to monoclinic space group Cc (no. 9) and NH(CH3)3SnBr3 belongs to the orthorhombic space group Pna21 (no. 33) by DSC, single-crystal X-ray diffraction and temperature-dependent SHG measurements, which clarify the former results. These results should pave the way for further studies of these materials in optoelectronics.

We consider the problem of resource allocation (in terms of subcarrier, bit and corresponding power) for QoS provisioning to real-time services in multiuser OFDM systems. A novel dynamic subcarrier and bit allocation algorithm is proposed for real-time services in multiuser OFDM systems. The proposed algorithm takes advantage of the instantaneous channel gain in subcarrier and bit allocation properly without relying on the nonlinear optimization technique, which is usually used in subcarrier and bit allocation when the instantaneous channel gain is considered. Therefore it avoids the corresponding computational complexity of the nonlinear optimization. The performance of the proposed algorithm is compared to other existing algorithms.