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Despite the fascinating optoelectronic properties of graphene, the power conversion efficiency (PCE) of graphene based solar cells remains to be lifted up. Herein, it is experimentally shown that the graphene/quantum wells/GaAs heterostructure solar cell can reach a PCE of 20.2% and an open-circuit voltage (V

Summary The static PN junction is the foundation of integrated circuits. Herein, we pioneer a high current density generation by mechanically moving N-type semiconductor over P-type semiconductor, named as the dynamic PN junction. The establishment and destruction of the depletion layer causes the redistribution and rebounding of diffusing carriers by the built-in field, similar to a capacitive charge/discharge process of PN junction capacitance during the movement. Through inserting dielectric layer at the interface of the dynamic PN junction, output voltage can be improved and designed numerically according to the energy level difference between the valence band of semiconductor and conduction band of dielectric layer. Especially, the dynamic MoS2/AlN/Si generator with open-circuit voltage of 5.1 V, short-circuit current density of 112.0 A/m2, power density of 130.0 W/m2, and power-conversion efficiency of 32.5% has been achieved, which can light up light-emitting diode timely and directly. This generator can continuously work for 1 h, demonstrating its great potential applications., Graphical Abstract, Highlights • High current density direct-current generator based on dynamic PN junctions • Dynamic equilibrium between establishment and destruction of the depletion layer • Capacitive discharge of PN junction capacitance caused by hot carriers rebounding • Enhance and design voltage numerically by inserting dielectric layer at the interface, Electrical Engineering; Energy Materials; Mechanical Engineering; Tribology

Summary Although perovskite has been widely explored in optoelectronic devices, it has been rarely explored as a Schottky junction. Here, we demonstrate a light- and mechanical-energy co-harvesting generator based on a dynamic metal/perovskite Schottky junction. In dark conditions, by moving Al over perovskite film (conductivity: 70.0 S/cm), output voltage and current density of −0.70 V and −41.1 A/m2, respectively, are achieved. As defects eliminate the photo-generated carriers in the static metal/perovskite junction under light illumination, the photoresponse is negligible. Strikingly, the output current of dynamic metal/perovskite junction under light illumination is enhanced by 3-fold compared with the dynamic junction in the dark condition. This nonlinear photo-enhanced effect is proposed as a result of strong interaction between the photo-generated and bound back carriers in the dynamic Schottky junction as well as the high light-absorption coefficient of perovskite. A flexible Al/perovskite generator has been demonstrated as a wearable energy-harvesting device.

The realization of p-type conduction in GaN and commercialized GaN light-emitting diodes (LED) is accepted as an advance in the development of human society. Conventionally, LED is based on PN junction and the quantum wells are introduced for confining electrons and holes, which improves the external quantum efficiency (EQE). Herein, we realized a graphene/AlGaN/GaN LED emitting double peaks at 430 nm and 560 nm. The blue peak at 430 nm is originated from the recombination process between holes injected from graphene/AlGaN heterostructure and electron produced from the tunnelling and avalanche multiplication process in p-type AlGaN/p-type GaN interface. Compared with the bare p-type AlGaN/GaN heterostructure without blue light emission, the graphene/p-AlGaN enhances the hole injection process through the band gap alignment and the mediate thickness of p-AlGaN is important taking the hole transport in AlGaN into consideration. The AlGaN/GaN interface confines the produced electrons and thus result in a high EQE of 55.8% under 5 mA current after intercalating an Al2O3 barrier at the interface between graphene and AlGaN/GaN. Moreover, the tunable graphene/AlGaN/GaN LED with different intensity of 430 nm has been demonstrated through changing the Fermi level of graphene by gating effect. The graphene/AlGaN heterostructure induced confinement effect can bring a novel type of LED, which can be optimized for special applications.

There is a rising prospective in harvesting energy from the environment, as in situ energy is required for the distributed sensors in the interconnected information society, among which the water flow energy is the most potential candidate as a clean and abundant mechanical source. However, for microscale and unordered movement of water, achieving a sustainable direct-current generating device with high output to drive the load element is still challenging, which requires for further exploration. Herein, we propose a dynamic PN water junction generator with moving water sandwiched between two semiconductors, which outputs a sustainable direct-current voltage of 0.3 V and a current of 0.64 μ A. The mechanism can be attributed to the dynamic polarization process of water as moving dielectric medium in the dynamic PN water junction, under the Fermi level difference of two semiconductors. We further demonstrate an encapsulated portable power-generating device with simple structure and continuous direct-current voltage output of 0.11 V, which exhibits its promising potential application in the field of wearable devices and the IoTs.

Silicon-based light emitting diodes (LED) are indispensable elements for the rapidly growing field of silicon compatible photonic integration platforms. In the present study, graphene has been utilized as an interfacial layer to realize a unique illumination mechanism for the silicon-based LEDs. We designed a Si/thick dielectric layer/graphene/AlGaN heterostructured LED via the van der Waals integration method. In forward bias, the Si/thick dielectric (HfO2-50 nm or SiO2-90 nm) heterostructure accumulates numerous hot electrons at the interface. At sufficient operational voltages, the hot electrons from the interface of the Si/dielectric can cross the thick dielectric barrier via the electron-impact ionization mechanism, which results in the emission of more electrons that can be injected into graphene. The injected hot electrons in graphene can ignite the multiplication exciton effect, and the created electrons can transfer into p-type AlGaN and recombine with holes resulting a broadband yellow-color electroluminescence (EL) with a center peak at 580 nm. In comparison, the n-Si/thick dielectric/p-AlGaN LED without graphene result in a negligible blue color EL at 430 nm in forward bias. This work demonstrates the key role of graphene as a hot electron active layer that enables the intense EL from silicon-based compound semiconductor LEDs. Such a simple LED structure may find applications in silicon compatible electronics and optoelectronics.

Since the discovery of two dimensional (2D) materials, there has been a gold rush for van der Waals integrated 2D material heterostructure based optoelectronic devices. Van der Waals integration involves the physical assembly of the components of the device. In the present work, we extended van der Waals integration from 2D materials to three-dimensional (3D) materials, and herein we uniquely designed a van der Waals contacted light emitting diode based on MoO

Recharging the batteries by wireless energy facilitates the long-term running of the batteries, which will save numerous works of battery maintenance and replacement. Thus, harvesting energy form radio frequency (RF) waves has become the most promising solution for providing the micropower needed for wireless sensor applications, especially in a widely distributed 4G/5G wireless network. However, the current research on rectenna is mainly focused on the integrated antenna coupled with metal-insulator-metal tunneling diodes. Herein, by adopting the plasmon excitation of graphene and quantum tunneling process between graphene and GaAs or GaN, we demonstrated the feasibility of harvesting energy from the 915 MHz wireless source belonging to 5G in the FR1 range (450 MHz–6 GHz) which is also known as sub-6G. The generated current and voltage can be observed continuously, with the direction defined by the built-in field between graphene and GaAs and the incident electromagnetic waves treated as the quantum energy source. Under the RF illumination, the generated current increases rapidly and the value can reach in the order of 10 -8 –10 -7 A. The harvester can work under the multiple channel mode, harvesting energy simultaneously from different flows of wireless energy in the air. This research will open a new avenue for wireless harvesting by using the ultrafast process of quantum tunneling and unique physical properties of graphene.

As the fast development of internet of things (IoTs), distributed sensors have been frequently used and the small and portable power sources are highly demanded. However, the present portable power source such as lithium battery has low capacity and need to be replaced or recharged frequently. A portable power source which can continuously generate electrical power in situ will be an idea solution. Herein, we demonstrate a wind driven semiconductor electricity generator based on a dynamic Schottky junction, which can output a continuous direct current with an average value of 4.4 mA (the maximum value of 8.4 mA) over 360 seconds. Compared with the previous metal/semiconductor generator, the output current is one thousand times higher. Furthermore, this wind driven generator has been explored to function as a turn counter due to its stable output and also to drive a graphene ultraviolet photodetector, which shows a responsivity of 35.8 A/W under the 365 nm ultraviolet light. Our research provides a feasible method to achieve wind power generation and power supply for distributed sensors in the future.

Searching for light and miniaturized functional device structures for sustainable energy gathering from the environment is the focus of energy society with the development of the internet of things. The proposal of a dynamic heterojunction-based direct current generator builds up new platforms for developing in situ energy. However, the requirement of different semiconductors in dynamic heterojunction is too complex to wide applications, generating energy loss for crystal structure mismatch. Herein, dynamic homojunction generators are explored, with the same semiconductor and majority carrier type. Systematic experiments reveal that the majority of carrier directional separation originates from the breaking symmetry between carrier distribution, leading to the rebounding effect of carriers by the interfacial electric field. Strikingly, NN Si homojunction with different Fermi levels can also output the electricity with higher current density than PP/PN homojunction, attributing to higher carrier mobility. The current density is as high as 214.0 A/m 2 , and internal impedance is as low as 3.6 k Ω , matching well with the impedance of electron components. Furthermore, the N-i-N structure is explored, whose output voltage can be further improved to 1.3 V in the case of the N-Si/Al 2 O 3 /N-Si structure, attributing to the enhanced interfacial barrier. This approach provides a simple and feasible way of converting low-frequency disordered mechanical motion into electricity.

related fabrication and measurement of devices

A type of broadband (325−980 nm) self-powered photodetector based on graphene/GaAs van der Waals heterojunction is reported. By simply spinning a layer of Ag nano-particles (Ag NPs) onto graphene/GaAs heterostructure, the responsivity and detectivity of our devices for the whole spectrum range are enhanced significantly. The maximum photocurrent responsivity of 210 mA W−1 (increased by 38%) and detectivity of 2.98 × 1013 Jones (increased by 202%) are achieved at 405 nm, which is about two or three orders of magnitude larger than other graphene based self-powered photodetectors. The mechanism of the improvement originates from the overlap the depletion region of graphene/GaAs heterostructure, the surface plasmon enhanced light field region below the surface and the light absorption region of the GaAs layer. The external quantum efficiency (EQE) measurement, transient photoluminescence (PL) test and the comparative theoretical simulation show that the surface plasmon enhancement should only be applicable for graphene/direct band gap semiconductor heterostructure, where the semiconductor should have a high optical absorption coefficient. The obtained high performance broadband photodetector with excellent detectivity is a promising candidate for many important optoelectronic applications, such as ultrasensitive image sensor in charge coupled displayer field, which requires colour sensors not only with high photo responsivity but also in a wide spectral range.

Near-infrared photodetectors (NIRPDs) have attracted great attention because of their wide range of applications in many fields. Herein, a novel self-driven NIRPD at the wavelength of 980 nm is reported based on the graphene/GaAs heterostructure. Extraordinarily, its sensitivity to light illumination (980 nm) is far beyond the absorption limitation of GaAs (874 nm). This means that the photocurrent originates from the separation of photo-induced carriers in graphene, which is caused by the vertically built-in electric field formed through the high quality van der Waals contact between graphene and GaAs. Moreover, after introducing NaYF4:Yb3+/Er3+ upconversion nanoparticles (UCNPs) onto the graphene/GaAs heterojunction, the responsivity increases to be as superior as 5.97 mA W-1 and the corresponding detectivity is 1.1 × 1011 cm Hz0.5 W-1 under self-driven conditions. This dramatic improvement is mainly ascribed to the radiative energy transfer from UCNPs to the graphene/GaAs heterostructure. The high-quality and self-driven UCNPs/graphene/GaAs heterostructure NIRPD holds significant potential for practical application in low-consumption and large-scale optoelectronic devices.

As a typical two-dimensional (2D) atomic thin material, the massless Dirac Fermions in graphene promise many unique physical properties, such as high carrier mobility and high light transmission. However, after a decade of research and a huge number of papers focusing on graphene, high performance graphene based optoelectronic devices is still lacked, which should be achieved for realizing competitive industrial graphene product. In this review, we point out high performance optoelectronic devices such as solar cells, photodetector and light emitting diodes can be demonstrated by properly marrying graphene with semiconductor. The fundamental physics of graphene/semiconductor heterostructure as well as its optoelectronic properties are comprehensively addressed. We suggest six strategies of improving the performance of graphene/semiconductor based optoelectronic devices. The outstanding light harvesting enhancement characteristic of surface plasmon is detailed represented to highlight its importance and potential. Especially, we indicate that graphene/semiconductor heterostructure solar cell can reach a power conversion efficiency of 30%.

A viable approach to enhance the photovoltaic performance of graphene (Gr)/semiconductor solar cells has been demonstrated. In order to take full advantage of the solar energy in the range of visible and ultraviolet light, InP and ZnO quantum dots (QDs) with band gaps of 2.4 eV and 3.3 eV, respectively, are simultaneously introduced to dope Gr by a photo-induced doping mechanism. Raman and photoluminescence measurements indicate that the photo-induced holes diffuse into Gr, leading to p-doping of Gr. As a result, the power conversion efficiency (PCE) of the Gr/GaAs heterostructure solar cell with good stability can be improved from 8.57% to 11.50%. Although this process is simple and feasible, we emphasize that the mixed semiconductor QDs enhanced Gr/semiconductor heterostructure solar cell is similar to the band gap engineering of traditional multi-junction bulk semiconductor solar cells.

Static heterojunction-based electronic devices have been widely applied because carrier dynamic processes between semiconductors can be designed through band gap engineering. Herein, we demonstrate a tunable direct-current generator based on the dynamic heterojunction, whose mechanism is based on breaking the symmetry of drift and diffusion currents and rebounding hot carrier transport in dynamic heterojunctions. Furthermore, the output voltage can be delicately adjusted and enhanced with the interface energy level engineering of inserting dielectric layers. Under the ultrahigh interface electric field, hot electrons will still transfer across the interface through the tunneling and hopping effect. In particular, the intrinsic anisotropy of black phosphorus arising from the lattice structure produces extraordinary electronic, transport, and mechanical properties exploited in our dynamic heterojunction generator. Herein, the voltage of 6.1 V, current density of 124.0 A/m 2 , power density of 201.0 W/m 2 , and energy-conversion efficiency of 31.4% have been achieved based on the dynamic black phosphorus/AlN/Si heterojunction, which can be used to directly and synchronously light up light-emitting diodes. This direct-current generator has the potential to convert ubiquitous mechanical energy into electric energy and is a promising candidate for novel portable and miniaturized power sources in the in situ energy acquisition field.

Putting a piece of graphene over p-GaN can form shallow P-N junction near the surface, which can act as light emitting diodes (LEDs) and promise many kinds of light manipulation methods. Herein, we introduce high performance surface plasmon enhanced graphene/p-GaN LEDs by inserting Ag nano-particles (Ag NPs) into the graphene/p-GaN interface. Bidirectional LEDs have been realized with a broad band emission from 550 nm to 650 nm at a forward bias of graphene side and a sharp emission of ~400 nm at a reversed bias of graphene. The emission intensity of graphene/Ag NPs/p-GaN is largely enhanced in both forward and reverse bias situation when compared with the bare graphene/p-GaN heterostructure, which is attributed to the surface plasmon resonance of Ag NPs. These results indicate that graphene/Ag NPs/p-GaN heterojunction is a promising candidate for high brightness LEDs.

Traditionally, Schottky diodes are used statically in the electronic information industry while dynamic or moving Schottky diode-based applications are rarely explored. Herein, a novel Schottky diode named "moving Schottky diode generator" is designed, which can convert mechanical energy into electrical energy by means of lateral movement between the graphene/metal film and semiconductor. The mechanism is based on the built-in electric field separation of the diffusing carriers in moving Schottky diode. A current-density output up of 40.0 A m-2 is achieved through minimizing the contact distance between metal and semiconductor, which is 100-1000 times higher than former piezoelectric and triboelectric nanogenerators. The power density and power conversion efficiency of the heterostructure-based generator can reach 5.25 W m-2 and 20.8%, which can be further enhanced by Schottky junction interface design. Moreover, the graphene film/semiconductor moving Schottky diode-based generator behaves better flexibility and stability, which does not show obvious degradation after 10 000 times of running, indicating its great potential in the usage of portable energy source. This moving Schottky diode direct-current generator can light up a blue light-emitting diode and a flexible graphene wristband is demonstrated for wearable energy source.

The overloaded energy cost has become the main concern of the now fast developing society, which make novel energy devices with high power density of critical importance to the sustainable development of human society. Herein, a dynamic Schottky diode based generator with ultrahigh power density of 1262.0 W m−2 for sliding Fe tip on rough p‐type silicon is reported. Intriguingly, the increased surface states after rough treatment lead to an extremely enhanced current density up to 2.7 × 105 A m−2, as the charged surface states can effectively accelerate the carriers through large atomic electric field, while the reflecting directions are regulated by the built‐in electric field of the Schottky barrier. This research provides an open avenue for utilizing the surface states in semiconductors in a subversive way, which can co‐utilize the atomic electric field and built‐in electric field to harvest energy from the mechanical movements, especially for achieving an ultrahigh current density power source.

By combining the surface plasmon enhancement technique with gating effect, a tunable blue lighting emitting diode (LED) based on graphene/Ag nanoparticles (NPs)-polymethyl methacrylate (PMMA)/graphene/p-GaN heterostructure has been achieved. The surface plasmon enhancement is introduced through spin-coating Ag nanoparticles on graphene/p-GaN heterostructure while the gating effect is demonstrated through a graphene/PMMA/graphene sandwich structure, where the top graphene layer acts as the gate electrode. Compared with initial graphene/p-GaN heterostructure LEDs, the electroluminescence (EL) emission intensity of Ag NPs/graphene/p-GaN heterostructure LEDs has been largely enhanced, attributing to the surface plasmon resonance (SPR) of Ag nanoparticles. The EL emission intensity of graphene/Ag NPs-PMMA/graphene/p-GaN heterostructure LEDs can further be gate-tunable effectively through exerting a static voltage between the sandwich structure, which tunes the Fermi level of graphene contacting with p-GaN. These results indicate that through sophisticated design, graphene/Ag NPs-PMMA/graphene/p-GaN heterostructure LEDs can be a potential candidate for many essential electronic and optoelectronic applications.

2D materials hold great potential for designing novel electronic and optoelectronic devices. However, 2D material can only absorb limited incident light. As a representative 2D semiconductor, monolayer MoS2 can only absorb up to 10% of the incident light in the visible, which is not sufficient to achieve a high optical-to-electrical conversion efficiency. To overcome this shortcoming, a "gap-mode" plasmon-enhanced monolayer MoS2 fluorescent emitter and photodetector is designed by squeezing the light-field into Ag shell-isolated nanoparticles-Au film gap, where the confined electromagnetic field can interact with monolayer MoS2 . With this gap-mode plasmon-enhanced configuration, a 110-fold enhancement of photoluminescence intensity is achieved, exceeding values reached by other plasmon-enhanced MoS2 fluorescent emitters. In addition, a gap-mode plasmon-enhanced monolayer MoS2 photodetector with an 880% enhancement in photocurrent and a responsivity of 287.5 A W-1 is demonstrated, exceeding previously reported plasmon-enhanced monolayer MoS2 photodetectors.

Y 2 O 2 S co-doped with Bi 3+ ,Eu 3+ phosphors were prepared and their luminescence properties under vacuum ultraviolet (VUV) excitation were investigated. Much stronger red emission for Y 2 O 2 S:Eu 3+ ,Bi 3+ were observed under 147 nm excitation than that for Y 2 O 2 S:Eu 3+ . Investigation on photoluminescence and calculation of electronic structure of Y 2 O 2 S:Eu 3+ ,Bi 3+ revealed that the Bi 3+ acts as a medium in energy transfer process and the great VUV luminescence enhancement of Y 2 O 2 S:Eu 3+ by doping Bi 3+ is due to effective energy transfer process: charge transfer (CT) transition of Y 3+ –O 2− → Bi 3+ → Eu 3+ . The Y 2 O 2 S:Eu 3+ ,Bi 3+ showed excellent optical properties when compared with the commercial (Y,Gd)BO 3 :Eu 3+ . Thus, the Y 2 O 2 S:Eu 3+ ,Bi 3+ would be a promising VUV-excited red phosphor.

Undoped and RE ions doped SrB2Si2O8 were successfully synthesized. After the application of UV and VUV spectroscopy measurements, we made a novel discovery that the emission of SrB2Si2O8:Eu prepared in air can be switched between red and blue by the different excitations. The information is that quite a part of Eu3+ was spontaneously reduced to Eu2+ in air. The PL properties of Eu2+ in VUV and Eu3+, Ce3+ and Tb3+ in UV–VUV region in SrB2Si2O8 were evaluated for the first time. The excitation mechanisms of the O2−–Eu3+ CT, Ce3+ f–d and Tb3+ f–d transitions in UV region as well as the Eu3+ f–d, O2−–Ce3+ CT, O2−–Tb3+ CT transitions and the host lattice absorption in VUV region were established. In addition, first principles calculation within the LDA of the DFT was applied to calculate the electronic structure and linear optical properties of SrB2Si2O8 and the results were compared with the experimental data.

Two dimensional material/semiconductor heterostructures offer alternative platforms for optoelectronic devices other than conventional Schottky and p–n junction devices. Herein, we use MoS 2 /GaAs heterojunction as a self-driven photodetector with wide response band width from ultraviolet to visible light, which exhibits high sensitivity to the incident light of 635 nm with responsivity as 321 mA/W and detectivity as 3.5×10 13 Jones (Jones=cm Hz 1/2 W −1 ), respectively. Employing interface design by inserting h-BN and photo-induced doping by covering Si quantum dots on the device, the responsivity is increased to 419 mA/W for incident light of 635 nm. Distinctly, attributing to the low dark current of the MoS 2 /h-BN/GaAs sandwich structure based on the self-driven operation condition, the detectivity shows extremely high value of 1.9×10 14 Jones for incident light of 635 nm, which is higher than all the reported values of the MoS 2 based photodetectors. Further investigations reveal that the MoS 2 /GaAs based photodetectors have response speed with the typical rise/fall time as 17/31 μs. The photodetectors are stable while sealed with polymethyl methacrylate after storage in air for one month. These results imply that monolayer MoS 2 /GaAs heterojunction may have great potential for practical applications as high performance self-driven photodetectors.

A ZnO quantum dot photo-doped graphene/h-BN/GaN-heterostructure ultraviolet photodetector with extremely high responsivity of more than 1915 A W−1 and detectivity of more than 1.02 × 1013 Jones (Jones = cm Hz1/2 W−1) has been demonstrated. The interfaced h-BN layer increases the barrier height at the graphene/GaN heterojunction, which decreases the dark current and improves the on/off current ratio of the device. The photo-doping effect increases the barrier height and carrier concentration at the graphene/h-BN/GaN heterojunction, thus the responsivity is improved from 1473 A W−1 to 1915 A W−1 and the detectivity is improved from 5.8 × 1012 to 1.0 × 1013 Jones. Moreover, all of the responsivity and detectivity values are the highest values among all the graphene-based ultraviolet photodetectors.

We demonstrate significantly improved photovoltaic response of monolayer molybdenum disulfide (MoS2)/indium phosphide (InP) van der Waals heterostructure induced by graphene quantum dots (GQDs). Raman and photoluminescence measurements indicate that effective charge transfer takes place between GQDs and MoS2, which results in n-type doping of MoS2. The doping effect increases the barrier height at the MoS2/InP heterojunction, thus the averaged power conversion efficiency of MoS2/InP solar cells is improved from 2.1% to 4.1%. The light induced doping by GQD provides a feasible way for developing more efficient MoS2 based heterostructure solar cells.

While the concept of responsible leadership has attracted scholarly interests for many years, there is no universally recognized definition. The current study represents the first attempt to understand the concept of responsible leadership, and forms a theoretical framework of responsible leadership for managers in the Chinese organizational context, from the perspective of Corporate Social Responsibility (CSR). Through a review of the literature, we constructed a theoretical framework of responsible leadership from the perspective of corporate social responsibility. The study creates a good start for the research on responsible leadership in Chinese organizational context, and has some important practical implication for management selection, assessment and training in China today.

The green phosphor BaAl11.9O19:0.1Mn2+ (BHA) was prepared by flux assisted solid-state reaction method. The effect of H3BO3 and the fire conditions on the crystal structure and luminescent properties under vacuum ultraviolet region (VUV) excitation of the phosphor were studied. Results of XRD patterns indicated that a pure phase BaAl12O19 could be achieved at the firing temperature above 1300 °C doping H3BO3 of 7.0 wt% as flux. The additions of flux H3BO3 promoted the solid reaction and reduced the temperature forming BaAl12O19:Mn2+ phosphor. Photoluminescent measurements under VUV excitation indicated that the luminescent intensity of the BaAl11.9O19:0.1Mn2+ enhanced by solid-state reaction adding appropriate amounts of H3BO3 as a flux.