Yongtao Tian

Strategy of Solution-Processed All-Inorganic Heterostructure for Humidity/Temperature-Stable Perovskite Quantum Dot Light-Emitting Diodes

Recently, a pressing requirement of solid-state lighting sources with high performance and low cost has motivated increasing research in metal halide perovskites. However, the relatively low emission efficiency and poor operation stability of perovskite light-emitting diodes (LEDs) are still critical drawbacks. In this study, a strategy of solution-processed all-inorganic heterostructure was proposed to overcome the emission efficiency and operation stability issues facing the challenges of perovskite LEDs. Solution-processed n-ZnO nanoparticles and p-NiO are used as the carrier injectors to fabricate all-inorganic heterostructured CsPbBr3 quantum dot LEDs, and a high-efficiency green emission is achieved with maximum luminance of 6093.2 cd/m2, external quantum efficiency of 3.79%, and current efficiency of 7.96 cd/A. More importantly, the studied perovskite LEDs possess a good operation stability after a long test time in air ambient. Typically, the devices can endure a high humidity (75%, 12 h) and a high working temperature (393 K, three heating/cooling cycles) even without encapsulation, and the operation stability is better than any previous reports. It is anticipated that this work will provide an effective strategy for the fabrication of high-performance perovskite LEDs with good stability under ambient and harsh conditions, making practical applications of such LEDs a real possibility.

High-performance perovskite photodetectors based on solution-processed all-inorganic CsPbBr3 thin films

Halide perovskites have attracted increasing attention in recent years as promising materials for optoelectronic devices. Herein, we report the use of a one-step spin-coating method for the preparation of all-inorganic CsPbBr3 perovskite thin film photodetectors. For the preparation of devices, the all-inorganic CsPbBr3 perovskite thin films were applied onto the interdigitated (IDT) patterned Au electrodes, and symmetrically structured photoconductive detectors were obtained. Photoresponse analysis reveals that a high photoresponsivity of 55 A W−1, an on/off photocurrent ratio of 1.06 × 105, a specific detectivity of up to 0.9 × 1013 Jones, an external quantum efficiency (EQE) of 16 700%, and a fast response speed of 430/318 μs were achieved in the fabricated CsPbBr3 photodetectors. Such performances are much better than those of most perovskite photodetectors from CsPbBr3 nanocrystals, and comparable with the highest results reported on organic–inorganic perovskite photodetectors. This work opens up an exciting opportunity for using all-inorganic perovskites for high-performance and low-cost photodetection applications.

Construction of MoS2/Si nanowire array heterojunction for ultrahigh-sensitivity gas sensor

Few-layer MoS2 thin films were synthesized by a two-step thermal decomposition process. In addition, MoS2/Si nanowire array (SiNWA) heterojunctions exhibiting excellent gas sensing properties were constructed and investigated. Further analysis reveals that such MoS2/SiNWA heterojunction devices are highly sensitive to nitric oxide (NO) gas under reverse voltages at room temperature (RT). The gas sensor demonstrated a minimum detection limit of 10 ppb, which represents the lowest value obtained for MoS2-based sensors, as well as an ultrahigh response of 3518% (50 ppm NO, ∼50% RH), with good repeatability and selectivity of the MoS2/SiNWA heterojunction. The sensing mechanisms were also discussed. The performance of the MoS2/SiNWA heterojunction gas sensors is superior to previous results, revealing that they have great potential in applications relating to highly sensitive gas sensors.

High-performance self-powered deep ultraviolet photodetector based on MoS2/GaN p–n heterojunction

High-performances deep-ultraviolet (DUV) photodetectors (PDs) are highly desired due to their great importance in numerous fields. In this study, self-powered MoS2/GaN p–n heterojunction PDs were constructed, which exhibited high sensitivity to DUV light illumination and pronounced photovoltaic behaviours. Photoresponse analysis revealed a high responsivity of 187 mA W−1, a high specific detectivity of 2.34 × 1013 Jones, a high linear dynamic range of 97.3 dB and fast response speeds of 46.4/114.1 μs (5 kHz) under a DUV light of 265 nm at zero bias voltage without an external power supply. Moreover, the MoS2/GaN p–n heterojunction PD could operate with excellent stability and repeatability in a wide frequency range over 10 kHz. The high performance could be attributed to the enhancment by the built-in electric field in the heterojunction. It is expected that such high-performance self-powered DUV PDs will have great potential applications in the future.

Polarized emission effect realized in CH3NH3PbI3 perovskite nanocrystals

In this study, we present a detailed investigation of the optical properties of organic–inorganic hybrid perovskite CH3NH3PbI3 nanocrystals (NCs). Temperature-dependent steady-state and time-resolved photoluminescence (PL) measurements were employed to understand the optical transition mechanisms and carrier recombination dynamics of CH3NH3PbI3 NCs. X-ray diffraction results showed a structural phase transition from the tetragonal to orthorhombic phase states during a cooling process although the PL results at low temperature revealed no signs of orthorhombic phase related emission. We analyzed in detail the possible reasons from three perspectives. In addition to the exciton related emission, two trap-mediated exciton emissions appear at low temperatures of 180 and 100 K because of the smaller binding energies of trapped excitons than that of free excitons. The corresponding exciton binding energy, optical phonon energy, and temperature sensitivity coefficient of the bandgap for CH3NH3PbI3 NCs were extracted from the experimental data. More importantly, we demonstrated the linearly polarized emission from the as-synthesized CH3NH3PbI3 NCs, and a linear polarization degree of 0.28 was obtained. It is reasonably believed that our obtained results open up possibilities for the development of new generation displays by using novel perovskite NCs with a high polarization property.

A room-temperature near-infrared photodetector based on a MoS2/CdTe p–n heterojunction with a broadband response up to 1700 nm

High-performance infrared photodetectors (PDs) have attracted much attention due to their great significance in military and industrial applications. The improvement of two-dimensional (2D) materials offers an open platform for designing various high-performance PDs, especially in the infrared region, which can overcome the drawbacks of the traditional epitaxial thin film based PDs, such as the complicated preparation processes, low-temperature operating conditions and inability to be miniaturized. In this work, a high-performance infrared PD based on a MoS2/CdTe p–n heterojunction with type-II band alignment was constructed and investigated. This PD showed a broadband photoresponse from 200 nm to 1700 nm, which is far beyond the band-gaps of MoS2 and CdTe. Moreover, a high responsivity, specific detectivity and fast response speed were achieved. These results demonstrate that the MoS2/CdTe p–n heterojunction has great potential in room-temperature infrared detection, and provide a way to design high-performance infrared PDs for other 2D materials.

In-situ fabrication of PtSe2/GaN heterojunction for self-powered deep ultraviolet photodetector with ultrahigh current on/off ratio and detectivity

The research of ultraviolet photodetectors (UV PDs) have been attracting extensive attention, due to their important applications in many areas. In this study, PtSe2/GaN heterojunction is in-situ fabricated by synthesis of large-area vertically standing two-dimensional (2D) PtSe2 film on n-GaN substrate. The PtSe2/GaN heterojunction device demonstrates excellent photoresponse properties under illumination by deep UV light of 265 nm at zero bias voltage. Further analysis reveals that a high responsivity of 193 mA·W–1, an ultrahigh specific detectivity of 3.8 × 1014 Jones, linear dynamic range of 155 dB and current on/off ratio of ~ 108, as well as fast response speeds of 45/102 μs were obtained at zero bias voltage. Moreover, this device response quickly to the pulse laser of 266 nm with a rise time of 172 ns. Such high-performance PtSe2/GaN heterojunction UV PD demonstrated in this work is far superior to previously reported results, suggesting that it has great potential for deep UV detection.

Self-powered solar-blind photodetector based on MoS2/β-Ga2O3 heterojunction

High-performance solar-blind photodetectors have attracted significant attention due to their great significance in military and industrial applications. In this work, a high-performance self-powered solar-blind photodetector based on a MoS2/β-Ga2O3 heterojunction was demonstrated. The photodetector exhibits a remarkable rectifying characteristic with a rectification ratio over 105 and excellent solar-blind photoresponse properties with a cut-off wavelength of 260 nm and a high rejection ratio of 1.6 × 103. Under light illumination of 245 nm (20.1 μW cm−2), the MoS2/β-Ga2O3 heterojunction photodetector shows a responsivity of 2.05 mA W−1 and a specific detectivity of 1.21 × 1011 Jones at zero bias voltage. Such high-performances of this photodetector are superior to other previously reported β-Ga2O3 based photodetectors, and provide a guideline to design high-performance self-powered solar-blind photodetectors.

High-efficiency and air-stable photodetectors based on lead-free double perovskite Cs2AgBiBr6 thin films

Halide perovskite-based photodetectors, because of their fundamental scientific importance and practical applications in the military and civil fields, have drawn worldwide attention in recent years. However, the toxicity and instability issues are major challenges for their mass production and commercialization. In this study, for the first time, we report the use of the one-step spin-coating method for the preparation of lead-free double perovskite Cs2AgBiBr6 thin films for photodetector applications. The morphology, crystallinity, and optical properties of the as-grown Cs2AgBiBr6 thin films were first investigated. Further, symmetrically structured photoconductive detectors were fabricated and characterized. The device performance was remarkable in terms of a high responsivity of 7.01 A W−1, an on/off photocurrent ratio of 2.16 × 104, a specific detectivity of 5.66 × 1011 Jones, an external quantum efficiency of 2146%, and a fast response speed of 956/995 μs. More importantly, the unencapsulated photodetectors demonstrate remarkable operational stability over the aging test (36 h, 35–45% humidity), and the photodetection ability can be almost maintained. Moreover, after storage for two weeks in ambient air, the proposed photodetectors can be efficiently sustained, demonstrating remarkable stability against water and oxygen degradation. Our results indicate that lead-free double perovskite Cs2AgBiBr6 is potentially an environmentally friendly alternative to fabricate high-efficiency and stable perovskite photodetectors for practical applications.

Hole-Injection Layer-Free Perovskite Light-Emitting Diodes

In this study, a dual-source vapor evaporation method was employed to fabricate the high-quality CsPbBr3 thin films with a good crystalline and high surface coverage. Temperature-dependent and excitation power-dependent photoluminescence measurements were performed to study the optical properties of the CsPbBr3 material. Further, based on the experimental data, the temperature sensitivity coefficient of band gap and exciton binding energy were estimated. More importantly, for the first time, we designed and prepared a hole-injection layer-free perovskite light-emitting diode (LED) based on the Au/MgO/CsPbBr3/n-MgZnO/n+-GaN structure, producing an intense green emission (∼538 nm) with a high purity. Besides, the device demonstrated a high luminance of 5025 cd/m2, an external quantum efficiency of 1.46%, a current efficiency of 1.92 cd/A, and a power efficiency of 1.76 lm/W. We studied in detail the current-voltage and electroluminescence properties of the prepared device and proposed the hole generation models and the carrier transport/recombination mechanisms to make these interesting characteristics certain. The results obtained would provide a new and effective strategy for the design and preparation of perovskite LEDs.