Organic-inorganic hybrid two-dimensional (2D) perovskites have recently attracted great attention in optical and optoelectronic applications due to their inherent natural quantum-well structure. We report the growth of high-quality millimeter-sized single crystals belonging to homologous two-dimensional (2D) hybrid organic-inorganic Ruddelsden-Popper perovskites (RPPs) of (BA)(MA) PbI ( n = 1, 2, and 3) by a slow evaporation at a constant-temperature (SECT) solution-growth strategy. The as-grown 2D hybrid perovskite single crystals exhibit excellent crystallinity, phase purity, and spectral uniformity. Low-threshold lasing behaviors with different emission wavelengths at room temperature have been observed from the homologous 2D hybrid RPP single crystals. Our result demonstrates that solution-growth homologous organic-inorganic hybrid 2D perovskite single crystals open up a new window as a promising candidate for optical gain media.

of more than 20% in the last few years. [1,2] Hybrid lead halide perov skites typically have a 3D ABX 3 (where, A = CH 3 NH 3 + (MA), B = Pb, and X = Cl, Br, and I) crystal structure con sisting of [PbI 6 ] and MA + units in their lattice framework and their band gaps can be tuned by halide engineering. [3][4][5] However, the key challenge in commer cializing 3D organic-inorganic hybrid perovskite photovoltaics is related to well known issues with longterm instability of devices under ambient conditions. [6,7] Recently, another class of 2D organicinorganic hybrid perovskite counterparts have attracted attention owing to their superior ambient stability and prom ising optoelectronic properties. [8][9][10][11][12][13][14] There is now considerable interest in 2D hybrid perovskite compounds, typi cally represented by the generic for mula (Aʹ) 2 (MA) n−1 M n X 3n+1 , where Aʹ is a longchain organic spacer, MA is small organic cation, M is a divalent metal, and n is the number of perovskite layers per unit cell. [15,16] These 2D hybrid halide perovskites exhibit a characteristic quantum well (QW)like structure owing to the selfassembled periodic array of perovskite [PbI 6 ] This work reveals the intrinsic carrier transport behavior of 2D organolead halide perovskites based on phase-pure homologous (n = 1, 2, and 3) Ruddelsden-Popper perovskite (RPP) (BA) 2 (MA) n−1 Pb n I 3n+1 single crystals. The 2D perovskite field effect transistors with high-quality exfoliated 2D perovskite bulk crystals are fabricated, and characteristic output and transfer curves are measured from individual single-crystal flakes with various n values under different temperatures. Unipolar n-type transport dominated the electrical properties of all these 2D RPP single crystals. The transport behavior of the 2D organolead halide hybrid perovskites exhibits a strong dependence on the n value and the mobility substantially increases as the ratio of the number of inorganic perovskite slabs per organic spacer increases. By extracting the effect of contact resistances, the corrected mobility values for n = 1, 2, and 3 are 2 × 10 −3 , 8.3 × 10 −2 , and 1.25 cm 2 V −1 s −1 at 77 K, respectively. Furthermore, by combining temperature-dependent electrical transport and optical measurements, it is found that the origin of the carrier mobility dependence on the phase transition for 2D organolead halide perovskites is very different from that of their 3D counterparts. Our findings offer insight into fundamental carrier transport behavior of 2D organic-inorganic hybrid perovskites based on phase-pure homologous single crystals. Field Effect Transistors

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In this study, a facile, fast, and cost-effective method for the synthesis of high-quality reduced graphene oxide sheets is reported by a microwave-assisted chemical reduction using hydroiodic acid/acetic acid as reducing agent. Exposure of graphene oxide (GO) with microwave irradiation (4 and 7 h) was found to be more rapid and sustainable reduction as compared to that of the conventional chemical reduction process (48 h). Formation of high-quality microwave-assisted reduced GO (mrGO) was ensured by means of electron microscopies, Raman, and infrared spectroscope studies. Furthermore, the antibacterial activity was evaluated for the mrGO, which showed good inhibitory effect against both Gram positive and Gram negative bacteria.

However, such photodetectors are still limited in practical application due to the lack of broadband absorption and slow response. Layered 2D materials of nano-thickness have been shown to possess good optoelectronic characteristics leading to great potential in overcoming the major obstacles of effective broadband and sensitivity. [5,6] For example, graphene as the first reported 2D material has drawn much attention due to its unique electrical and mechanical properties. [7,8] However, graphene exhibits major limitations on the optoelectronic application, such as the weak light absorbance, large dark current, and fast carrier recombination due to zero bandgap. [9,10] There are many alternative layered 2D materials that have been tested and reported since, including transition-metal dichalcogenides (TMDC), [11-15] indium selenide (InSe), [16] hexagonal boron nitride (h-BN), [17] and black phosphorus. [18] In the class of layered 2D materials, TMDC holds great promise because of their direct band gap, strong absorption, and atomic-scale thickness with favorable electronic and mechanical properties. 2D transition-metal dichalcogenides have attracted significant interest in recent years due to their multiple degrees of freedom, allowing for tuning their physical properties via band engineering and dimensionality adjustment. The study of ternary 2D hafnium selenosulfide HfSSe (HSS) high-quality single crystals grown with the chemical vapor transport (CVT) technique is reported. An as-grown HSS single crystal exhibits excellent phototransistor performance from the visible to the near-infrared with outstanding stability. A giant photoresponsivity (≈6.4 × 10 4 A W −1 at 488 nm) and high specific detectivity (≈10 14 Jones) are exhibited by a device fabricated by exfoliating singlecrystal HSS of nano-thickness on a rigid Si/SiO 2 substrate. The application of HSS single crystal is extended to yield a sensible flexible photodetector of photoresponsivity up to ≈1.3 A W −1 at 980 nm. The photoresponsivity of CVT-grown HSS single crystal is significantly larger than those fabricated with other existing Hf-based chalcogenides. The results suggest that the layered multi-elemental 2D chalcogenide single crystals hold great promise for future wearable electronics and integrated optoelectronic circuits.