Chengxue Huo’s research while affiliated with Nanjing University of Science and Technology and other places

All-inorganic halide perovskites have made significant achievements in electronics, optoelectronics, and other fields due to their unique physical and chemical properties. However, the researchers focus on the traditional planar field-effect transistors, which have limited electrical performance and applications due to their planar structure with a long channel length. Here, we report a vertical field-effect transistor (VFET) based on the CsPbBr3 microplatelet grown by van der Waals epitaxial growth. The VFET is achieved by a direct evaporation method utilizing a height difference between the CsPbBr3 single-crystal and graphene substrate. Compared with the traditional planar structure transistors, the device exhibits more excellent performance, such as high carrier mobility of 7.3 cm2 V-1 s-1 at room temperature and high on/off radio over 106. The trap-state density of CsPbBr3 single-crystal is calculated to be as lower as 2.3×1015 cm-3 by space-charge-limited currents, which further proves its excellent crystallinity. Also, we have firstly fabricated a MoS2/CsPbBr3 heterostructure inverter with the vertical structure, which could implement the "No" function in logic operations. This work opens a new pathway for the practical application of all-inorganic halide perovskites in future electronics.

Downsizing alloy anode materials are demonstrated as an efficient strategy to alleviate the volume expansion and prolong the cycling performance for lithium-ion storage. However, the dimension and size dependent Li-ion diffusion and battery performances have scarcely explored. This work has been conducted to determine the tailoring engineering for a natural layered material, β-phase Sb and identify the dimension and size effects on the lithium-ion storage performance, which is of particular case with respect to alloy anode materials at present. Two kinds of tailoring engineering, respectively in vertical direction and omnidirection, are adopted to produce few layer antimonene and Sb nanoparticles (NPs) by regulating ultrasonication. In absence of helpful fluoroethylcarbonate additives, the tailoring engineering can still improve the cycling stability and the reversible capacity, lateral size dominated 2D antimonene exhibits higher rate performance than Sb NPs. In-situ electron microscopy analysis reveals the limited expansion of lateral size for 2D antimonene upon lithiation. Theoretical simulation reveals that the in-plane diffusion energy barrier (0.25 eV) for layered β-phase Sb is much smaller than the diffusion energy barrier across its interlayers (1.14 eV). Therefore, the unique 2D antimonene with large lateral size can achieve better high-rate performance than Sb NPs, also stable capacity for lithium-ion storage.

Combining halide perovskites and 2D materials to form heterojunctions is a potential excellent strategy to design high‐performance phototransistors. However, a standard perovskite/2D material heterojunction is not fully realized, because either of the active material usually directly bridges across the opposite metal electrodes in the transistor platform. Here, phototransistors are fabricated based on high‐quality van der Waals grown CsPbBr3 and MoS2, in which CsPbBr3 and MoS2 are overlapped only within the transistor channel. The phototransistors based on this standard CsPbBr3/MoS2 heterojunction exhibit excellent optical detection ability and field‐effect characteristics at a drain–source voltage as small as 0.5 V. The rise and fall times of the phototransistor are 2.5 and 1.8 ms, respectively. The hole mobility is calculated to be 0.08 cm2 V−1 s−1 in darkness, and 0.28 cm2 V−1 s−1 under the 442 nm laser illumination. All of the measurements are conducted at room temperature in ambient air, indicating the excellent robustness of the CsPbBr3/MoS2 heterojunction. This work provides a new strategy to minimize the device size by using low‐voltage‐driven, air‐stable perovskite/2D material heterojunctions. Van‐der‐Waals heterojunctions based on two‐dimensional (2D) materials and thin halide perovskite single crystals can effectively combine the advantages of both 2D materials and halide perovskites. The optimized optical and electrical tuning of CsPbBr3/MoS2 band alignment can effectively separate the holes and electrons excited by photons, which leads to a low‐voltage‐operated phototransistor.

Halide perovskite microplatelets (HPeMs) with ultrahigh crystallinity and large lateral dimension provide a good potential for realizing new micrometer‐scale light sources. However, the difficulty of obtaining uniform microplatelet thin films imposes the impediment for getting light sources in the conventional vertical configuration. Here, bright electroluminescence (EL) from a light‐emitting device based on solution‐processed large HPeMs is obtained using alternating current (AC) voltage in a planar device configuration. The bright and stable EL driven by 50 Hz demonstrates that this AC‐driven light‐emitting device can directly couple with household power supplies, thereby simplifying the electrical circuit modulation. The low‐frequency‐driven capability can be originated from the high charge carrier mobility and long carrier lifetime in perovskites, i.e., the hole accumulation can be reduced near the metal electrode to allow more hole injection, and more long‐lifetime holes can wait for injected electrons to recombine. Moreover, the shift of peak position and full‐wavelength‐at‐half‐maximum in the temperature‐dependent EL spectra reveals that the electric‐induced ionized scattering centers and related ion migration might have been neglected in the widely studied temperature‐dependent photoluminescence measurements. This work demonstrates an alternative operating mechanism and light‐emitting device configuration for obtaining EL from perovskites, offering a new manner to get novel micrometer‐scale perovskite light sources. Electroluminescence (EL) is obtained from a light‐emitting device based on solution‐processed large CsPbBr3 microplatelets using alternating current (AC) voltage. The EL driven by 50 Hz suggests that this AC‐driven light‐emitting device can directly couple with household power supplies, thereby simplifying the electrical circuit modulation. The light emission at 50 Hz is still tunable after storing the device for nearly three months.

Two-dimensional (2D) antimonene is a promising anode material in sodium-ion batteries (SIBs) because of its high theoretical capacity of 660 mAh g⁻¹ and enlarged surface active sites. However, its Na storage properties and sodiation/desodiation mechanism have not been fully explored. Herein, we propose the sodiation/desodiation reaction mechanism of 2D few-layer antimonene (FLA) based on results acquired by in situ synchrotron X-ray diffraction, ex situ selected-area electron diffraction and theoretical simulations. Our study shows that the FLA undergoes anisotropic volume expansion along the a/b plane and exhibits reversible crystalline phase evolution (Sb ⇋ NaSb ⇋ Na3Sb) during cycling. Density-functional theory calculations demonstrate that the FLA has a small Na ion diffusion barrier of 0.14 eV. The FLA delivers a larger capacity of 642 mAh g⁻¹ at 0.1 C (1 C = 660 mA g⁻¹) and a high rate capability of 429 mAh g⁻¹ at 5 C, and maintains a stable capacity of 620 mA g⁻¹ at 0.5 C with 99.7% capacity retention from 10th to 150 th cycle. Considering the 660 mAh g⁻¹ theoretical capacity of Sb, the electrochemical utilization of Sb atoms of FLA is as high as 93.9% at a rate of 0.5 C for over 150 cycles, which is the highest capacity and Sb utilization ratio reported so far. Our study discloses the Na storage mechanism of 2D FLA, boosting promising applications of 2D materials for advanced SIBs.

Inorganic halide perovskites (IHPs) exhibited promising potentials for high-performance wide-band photodetectors (PDs) due to their high light absorption coefficients, long carrier diffusion length and wide light absorption ranges. Here, we report two-dimensional (2D) CsPbBr3/PCBM heterojunctions for sensitive, fast and flexible photodetectors, whose performances can be greatly boosted by the charge transfer through the energy-aligned interface. The 2D CsPbBr3 nanosheets (NSs) with high crystallinity were fabricated via a simple solution-process at room temperature, and then assembled into flexible heterojunctions films with polymerphenyl-C61-butyric acid methyl ester (PCBM). Significantly, the efficient and fast charge transfer at the heterojunctions interface was evidenced by the obvious photoluminescence quenching and variation of recombination dynamics. Subsequently, such heterojunctions PD exhibited an enhanced responsivity of 10.85 A/W and an ultrahigh detectivity of 3.06 × 1013 Jones. In addition, the PD shows a broad linear dynamic range (LDR) of 73 dB, a fast response speed with rise time of 44 μs and decay time of 390 μs, respectively. Moreover, the PD lying on polyethylene terephthalate (PET) substrates exhibited an outstanding mechanical flexibility and a robust electrical stability. These results could provide a new avenue for integration of 2D perovskites and organic functional materials and for high-performance flexible PDs.

Transition metal dichalcogenides (TMDs) are promising candidates for flexible optoelectronic devices due to their special structures and excellent properties, but the low optical absorption of the ultrathin layers greatly limits the generation of photocarriers and restricts the performance. Here, we integrate the all-inorganic perovskite CsPbBr3 nanosheets with MoS2 atomic layers, and take the advantage of the large absorption coefficient and high quantum efficiency of the perovskites, to achieve excellent performance of the TMDs based photodetector. Significantly, the interfacial charge transfer from the CsPbBr3 to MoS2 layer has been evidenced by the observed photoluminescence quenching and shortened decay time of the hybrid MoS2/CsPbBr3. Resultantly, such hybrid MoS2/CsPbBr3 photodetector exhibits a high photoresponsivity of 4.4 A/W, an external quantum efficiency of 302%, and a detectivity of 2.5×1010 Jones due to the high efficient photoexcited carrier separation at the interface of MoS2 and CsPbBr3. The photoresponsivity of this hybrid device presents an improvement of three orders of magnitude compared with a MoS2 device without CsPbBr3. The response time of the device is also shortened from 65.2 ms to 0.72 ms after coupling with MoS2 layers. The combination of the all-inorganic perovskite layer with high photon absorption and the carrier transport TMD layer may pave the way for novel high performance optoelectronic devices.

Nowdays, the research on perovskite transistors is still in its infancy, despite that perovskite based solar cells and light emitting diodes have been widely investigated. Two major hurdles exist before obtaining reliable perovskite based transistors: the processing difficulty for their sensitivity to polar solvents, and unsatisfactory perovskite quality on the transistor platform. Here, for the first time, we report on high-performance all-inorganic perovskite FETs profited from both van-der-Waals epitaxial boundary-free ultrathin single-crystals and completely dry-processed transfer technique without chemical contaminant. These two crucial factors ensure the unprecedented high-quality perovskite channels. The achieved FET hole mobility and on-off ratio reach 0.32 cm2V-1s-1 and 6.7×10^3, respectively. Moreover, at the low temperature, the mobility and on-off ratio can be enhanced to be 1.04 cm2V-1s-1 and 1.3×10^4. This work could open the door for the FET applications based on perovskite single crystals.

Recently, both light-to-electricity and electricity-to-light conversion efficiencies of perovskite achieved breakthrough, e.g. 22.1% for solar cells and 11.7% for light-emitting diodes (LEDs), so the next fatal problem towards practical application, the device stability, became the key issue in this field. Here, for the first time, we report the all-inorganic LEDs including inorganic perovskite emitters (CsPbBr3) and inorganic charge transport layers (CTLs) with emphasis on the significantly improved device stability. The quantum dot LEDs (QLEDs) were fabricated according to ITO/NiO/CsPbBr3 QDs/ZnO/Al device confriguration. On the one hand, the all-inorganic LED lifetime under 65% humidity corresponding to 70% electroluminescence (EL) conservation rate can be improved up to 3.5 times when compared with LEDs adopting conventional organic CTLs due to the intrinsic chemical stability of these inorganic CTLs and their hydrophobic surfaces. Furthermore, as a surprise, the bare all-inorganic LED without encapsulation can work in water for about 20 seconds, which is over 10 times more sustainable than the organic-inorganic LED, which proves the excellent water-isolation ability. On the other hand, the all-inorganic QLEDs show the lowest turn-on voltage of 2.4 V among all the reported CsPbBr3 QLEDs because the inorganic CTLs possess well-matched energy band alignments with CsPbBr3, and hence resulting in efficient carrier injection. This work paves a way, constructing all-inorganic devices, for the stable perovskite photovoltaic and light-emitting devices.