Build-in Electric Field Research Articles

Strain-Manipulated Photovoltaic and Photoelectric Effects of the MAPbBr3 Single Crystal.

Lead halide perovskite materials, such as MAPbBr3 and MAPbI3, show excellent semiconductor properties, and thus, they have attracted a lot of attention for applications in solar cells, photodetectors, etc. Here, a periodic strain can dynamically manipulate the build-in electric field (Ebi) of the depletion region with piezoelectricity at the Au/MAPbBr3 interface. As a result, the photovoltaic short-circuit current density (Jsc) and the open-circuit voltage (Voc) are increased by 670 and 82%, respectively, by applying an external strain upon an asymmetric solar-cell-like Au/MAPbBr3/Ga structure. Furthermore, the equivalent piezoelectric d33 values of ∼3.5 pC/N are confirmed in the Au/MAPbBr3/Au structure with both the sinusoidal strain and the 405 nm light illumination with 220 mW/cm2 upon one semitransparent Au electrode. This study not only proves that pressure can effectively enhance the energy conversion efficiency of the halide perovskite-based solar cells and light detectors but also supposes a multifunctional sensor, which can detect light intensity, sense dynamic pressure, explore accelerated speed, etc. simultaneously.

Enhanced photocatalytic hydrogen evolution by piezoelectric effects based on MoSe2/Se-decorated CdS nanowire edge-on heterostructure

The build-in electric field by the construction of heterojunction is one of the most promising strategies to suppress the recombination of photogenerated carriers. Here, we reported a piezo-photocatalytic system composed of Se-decorated CdS nanowires and few-layered edge-on MoSe2 nanosheets for efficient H2 generation by two-pot hydrothermal synthesis. The few-layered MoSe2 exposed abundant edge sites for hydrogen evolution reaction (HER). The activity of 20-MoSe2/CdS0.95Se0.05 (20-MS/CSS, with 20 mol% of MoSe2 loading) nanocomposite casted a remarkable photocatalytic HER performance, with a rate of 47.3 mmol h−1 g−1. Moreover, MoSe2 nanosheets deformed to generate the piezoelectric polarization field under magnetic stirring, which rendered efficient separation of photogenerated carriers, resulting in a piezo-photocatalytic synergistic effect. As a result, the HER of 20-MS/CSS at 900 rpm for piezo-photocatalysis was 59.1 mmol h−1 g−1, which was 1.25 times that of 20-MS/CSS for photocatalysis. Meanwhile, the photoelectrochemical measurements further visualized the piezo-photoelectric synergy. This study exposes a new way for utilizing mechanical energy to improve photocatalytic performance, and achieving high piezo-photocatalysis.

Preparation of high performance Ga2O3 based ultraviolet photodetector by CVD

Here, β-Ga2O3 films have been grown on c-Al2O3 and p-GaN substrates by chemical vapor deposition method to fabricate solar-blind ultraviolet photodetectors with MSM-type planar structure and pn-junction vertical structure respectively. The β-Ga2O3 films grown with domain growth mode exhibit high crystallinity and flat surface, so the fabricated MSM-type photodetector shows spectral peak responsivity of 1.83 A/W at 254 ​nm and photo-to-dark current ratio of 104 under 25 ​V bias with 20% oxygen fraction and 120 sccm flow rate. On this basis, the constructed vertical structured β-Ga2O3/p-GaN heterojunction photodetector shows peak responsivity of 1.99 A/W under 25 ​V for the junction effect between β-Ga2O3 and p-GaN. Meanwhile, spectral responsivity peak of 1.36 ​× ​10−4 A/W at 0V claims significant self-powered effect induced by build-in electric field between β-Ga2O3 and p-GaN. These results confirm that high performance β-Ga2O3 solar-blind ultraviolet photodetectors can be obtained by simple chemical vapor deposition method.

Controllable oxygen-doping of two-dimensional heterostructure as diode-type gas sensor with high performance

To meet the low energy consumption requirement of the Internet of things, there is an eagerness for 2D gas sensors to realize the ultralow-power or self-powered sensing at room temperature. Here, we demonstrate the controllable Oxygen-doping of SnS2/G heterostructure as a diode-type gas sensor with excellent and robust performances. The oxygen substitution controlled by ion irradiation modifies the homogeneous SnS2/G heterostructure into a heterogeneous SnS2-0.22O0.22/G-SnS2/G. The boundary of SnS2-0.22O0.22/G-SnS2/G forms a lateral Schottky junction, which outputs a stable open-circuit voltage of 1.5 V under the indoor light illumination. Adsorbed with gas molecules, the SnS2-0.22O0.22/G-SnS2/G junction has the variation of the photoconductance instead of the build-in electric field, ensuring the linear response to the gas concentration. This diode-type gas sensor exhibits long-term stability for at least 50 days (50th−100th day) and has an ultrafast gas-sensing performance with a response/recovery time of ∼54 s/9.2 s. Besides, it exhibits high selectivity to NO2 (42.8%) compared to gas species of H2S (0.6%), SO2 (7.8%), and NH3 (0%), based on different sensitivities. This work presents controllable oxygen doping as a novel avenue for preparing extremely energy-efficient sensors with fast response/recovery, linear response, and robust performances catering to future ubiquitous and real-time sensing requirements.

Blue phosphorene/MoSi2N4 van der Waals type-II heterostructure: Highly efficient bifunctional materials for photocatalytics and photovoltaics

Converting solar energy into electric power or hydrogen fuel is a promising means to obtain renewable green energy. Here, we design a two-dimensional blue phosphorene (BlueP)/MoSi2N4 van der Waals heterostructure (vdWH) and investigate its potential application in photocatalysis and photovoltaics using first-principles calculations. We find that the BlueP/MoSi2N4 vdWH possesses type-II band structure with a large build-in electric field, thus endowing it with a potential ability to separate photogenerated electron–hole pairs. The calculated band-edge positions show that the heterostructure is a very promising water-splitting photocatalyst. Its solar-to-hydrogen efficiency (η STH) can reach up to 15.8%, which is quite promising for commercial applications. Furthermore, the BlueP/MoSi2N4 vdWH shows remarkably light absorption capacity and distinguished maximum power conversion efficiency (η PCE) up to 10.61%. Remarkably, its η PCE can be further enhanced by the external strain: the η PCE of 21.20% can be obtained under a 4% tensile strain. Finally, we determine that adjusting the number of the BlueP sublayer is another effective method to modulate the band gaps and band alignments of the heterostructures. These theoretical findings indicate that BlueP/MoSi2N4 vdWH is a promising candidate for photocatalyst and photovoltaic device.

Tunable electronic properties of two-dimensional C3N/antimonene van der Waals heterostructure

In this work, we construct a C3N/antimonene van der Waals heterostructure to investigate its structural and electronic properties using first-principles calculations. The C3N/antimonene heterostructure exhibits an indirect band gap of 0.143 eV with a type-II band alignment. Electrons transferring from C3N to antimonene layer introduce a build-in electric field which can be used to prevent recombination of the photoexited electron–hole pairs. By applying vertical strain, band gap value of the heterostructure can be tuned in a range from 0 to 0.318 eV. A type-II to type-I band alignment transition occurs at a interlayer distance of sim3.2 Å, and the heterostructure experiences a semiconductor to metal transition with a interlayer distance of sim3.7 Å. Moreover, structural and electronic properties of C3N/antimonene heterostructure show modulation under in-plane biaxial strain. A semiconductor to metal transition takes place when strain reaches −2.0%. Moreover, with the increase of compressive strain, buckling degree of the heterostructure increases, and band gap of the heterostructure increases to 0.645 eV at strain of −5.0%. In addition, band gap value of the heterostructure varies almost linearly with vertical electric field of −0.2–0.2 V Å−1, and type-II band alignment can be maintained in this range. Thus, these results indicate that C3N/antimonene heterostructure has great potential in the field of multifunctional optoelectronic devices.

Hybrid heterostructure of transition metal dichalcogenides as potential photocatalyst for hydrogen evolution

Transition metal dichalcogenides (TMDCs) heterostructure with property diversity is of scientific and technological interest for nanoelectronics and photoelectronic devices. Herein, we investigate electronic properties of TMDCs hybrid heterostructures, i.e., (WS2-MoS2)/WS2, (WS2-MoS2)/MoS2 and WS2/(WS2-MoS2)/WS2 heterostructures. From analyses of energetics, charge transfer and interaction strength, we find there is a synergistic effect, i.e., strong intralayer and moderate interlayer interaction, in these hybrid heterostructures. Electrostatic potential analysis implies there is a build-in electric field at interfaces of these hybrid heterostructures, which would influence the migration of photoinduced carriers. Combination of build-in electric field with band offset calculations, separation mechanism of photoinduced carriers is discussed. Our calculated results show that (WS2-MoS2)/WS2 and WS2/(WS2-MoS2)/WS2 hybrid heterostructures are potential type-II photocatalyst for hydrogen evolution. (WS2-MoS2)/MoS2 heterostructure is a candidate material for infrared laser light emitting devices due to its type-I band alignment. Finally, the influence of strain on band gap of (WS2-MoS2)/WS2 hybrid heterostructure is also investigated. We believe our study suggests potential direction for fabrication of novel electronic and photoelectric devices based on TMDCs heterostructures.

Enhanced visible light-driven photocatalytic destruction of decontaminants over Bi2O3/BiVO4 heterojunctions with rich oxygen vacancies

Bi2O3/BiVO4 heterojunctions with enriched oxygen vacancies (OVs) were prepared by a hydrothermal method. High-resolution transmission electron microscope (HRTEM), electron paramagnetic resonance (EPR), surface photovoltage spectra (SPS) and photoelectrochemical measurements confirm that the construction of Bi2O3/BiVO4 heterojunctions, and the build-in electric field between Bi2O3 and BiVO4 facilitates transfer of charge pairs and increases the lifetime of carriers, the existence of oxygen vacancies (OVs) plays a leading role in the improvement of photocatalytic performance. Photocatalytic activity of the constructed catalysts was systematically assessed by destruction of tetracycline (TC) and rhodamine B (RhB). According to experimental results, photogenerated carrier transfer mechanism was proposed.

Effects of conjugated structure on electronic and transport properties in organic–inorganic hybrid superlattices Cd2Se2(C2H4N2)1/2

By inducing π-conjugated organic molecule C2H4N2 in group II–VI based CdSe network structure materials, the band structures and carrier transport of organic–inorganic hybrid superlattices Cd2Se2(C2H4N2)1/2 were investigated via first-principles calculations based on the density functional theory. With different stacking patterns, it is found that the carrier mobility can be modulated by 5–6 orders of magnitude. The physical mechanism of the high carrier mobility in the hybrid structures has been revealed, which means dipole organic layers realize electron delocalization via electrostatic potential difference and build-in electric field. Our calculations shown that the dipole organic layers originate from asymmetric π-conjugated organic molecules and the charges movement between molecules, while symmetric organic molecules tend to electrostatic balance. And although the electronic transport properties were highly restrained by the flat bands of organic layers around Fermi energy in most structures, we found that the collective electrostatic effect can lead to very high electron mobility in AA1 and AA2 stacking systems, which might be attributed to the superposition of molecule electrostatic potential along with electrons transfer between molecules. Furthermore, it is also found that the anisotropy of electron mobility can be modulated via the difference directions of dipole layers.

Design of a two-dimensional interplanar heterojunction for catalytic cancer therapy

Limited substrates content is a major hurdle dampening the antitumor effect of catalytic therapy. Herein, a two-dimensional interplanar heterojunction (FeOCl/FeOOH NSs) with ·OH generation under ultrasound irradiation is fabricated and utilized for catalytic cancer therapy. This interplanar heterojunction is prepared through replacing chlorine from iron oxychloride with hydroxyl. Benefiting from the longer hydroxyl bond length and enhanced affinity with water, the alkali replacement treatment integrates interplanar heterojunction synthesis and exfoliation in one step. In particular, a build-in electric field facilitated Z-scheme interplanar heterojunction is formed due to the aligning Fermi levels. The holes on the valence band of FeOCl have great ability to catalyze O2 evolution from H2O, meanwhile, the generated O2 is immediately and directly reduced to H2O2 by the electrons on the conductive band of FeOOH. The self-supplying H2O2 ability guarantees efficient ·OH generation via the Fenton-like reaction catalyzed by FeOCl/FeOOH NSs, which exhibits excellent anti-tumor performance.

Grating Perovskite Enhanced Polarization-Sensitive GaAs-Based Photodetector

In this work, we demonstrate the fabrication of GaAs photodetector with grating perovskite (G-PVK) for a broadband enhanced ultraviolet (UV)-near-infrared (NIR) photodetection. The device shows a peak photoresponse under 530-nm illumination, presenting a responsivity of 0.3 A/W, a specific detectivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.24\,\,\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> Jones, and 0.6/0.56 ms for rise/fall time, respectively. Compared to the device without PVK, the dark current was suppressed by two orders of magnitude and the photoresponse was enhanced up to 215%. This should be ascribed to the effective spatial separation of the vertical build-in electric field between GaAs and G-PVK and the enhanced light trapping arising from the diffraction grating. The well-aligned grating also shows a high sensitivity to the polarized light, giving rise to a peak-to-valley ratio <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{{\mathrm {max}}} / {I}_{{\mathrm {min}}}$ </tex-math></inline-formula> of about 2.14. This suggests the potential application of the device in the polarization-sensitive imaging system.

Interfacial and build-in electric fields rooting in gradient polyelectrolyte hydrogel boosted heavy metal removal

With the aggravation of pollutants damage to the environment, it is crucial yet rather challenging to design powerful matrixes for nanomaterials with high ions permeability and migration, as well as multiple exposed active sites. However, most of the current nanomaterial matrixes just act as carrier supporters with introduced invalid mass. Here, a gradient natural polycation electrolyte (chitosan) hydrogel was engineered as nanomaterials matrix to boost anionic heavy metals removal such as antimonate (Sb(V)) and arsenate (As(V)) for the first time, based on the generated interfacial and build-in electric potentials due to the diffusion of counterions. The resulting dual electric potentials allow for rapid diffusion and removal efficiency of heavy metal ions. Exemplified by Sb(V) removal, the chitosan gradient hydrogel matrixes with embedded UiO-66 MOFs exhibited a 3-fold higher removal velocity than the homogeneous hydrogel matrix, and their removal efficiencies were also promoted by gathering on the high charge density side of hydrogels. In contrast to the other reported matrix materials without driving force, the gradient polyelectrolyte hydrogel can greatly boost the removal efficiency and shorten the treatment times. This study offers inspirations on eliminating heavy metal contaminations based on self-driving forces stemming from the heterogeneous structure of materials.

Rapid dual-channel electrons transfer via synergistic effect of LSPR effect and build-in electric field in Z-scheme W18O49/BiOBr heterojunction for organic pollutants degradation

The development of Z-scheme heterojunction is a frequently-used way to boost photogenerated electrons separation and migration for obtaining excellent photocatalytic performance. Hence W18O49/BiOBr Z-scheme heterojunction photocatalyst was macroscopically synthesized via high-production mechanical ball milling method. Attributed to the synergistic effect of Z-scheme heterojunction and LSPR effect, W18O49/BiOBr composites possessed remarkably strengthened visible light absorption and rapid photogenerated electrons migration performance. In comparison with pure BiOBr, 2 wt% W18O49/BiOBr composites possessed highly photocatalytic degradation performance for methyl orange (MO), tetracycline hydrochloride (TC) and good stability. Consequently, this work extends the application of ball milling method in photocatalyst preparation and contaminant treatment field.

Preparation of Ag@CuFe2O4@TiO2 nanocomposite films and its performance of photoelectrochemical cathodic protection

• Ag@CuFe 2 O 4 @TiO 2 nanocomposite has excellent photochemical cathodic protection performance for 304 stainless steel. • The protective potential of Ag@CuFe 2 O 4 @TiO 2 is 14.8 times that of pure TiO 2 nanowires. • Ag@CuFe 2 O 4 @TiO 2 can also provide cathodic protection for 304 stainless steel in dark conditions. • The heterojunction electric field of Ag@CuFe 2 O 4 @TiO 2 enhances the separation ability of photogenerated electrons and holes. A Ag@CuFe 2 O 4 @TiO 2 nanocomposite film with high performance of photogenerated cathodic protection was prepared by hydrothermal and photoreduction methods. The results showed that when the CuFe 2 O 4 hydrothermal reaction time was 6 h and the AgNO 3 concentration was 0.1 M, the Ag@CuFe 2 O 4 @TiO 2 nanocomposite material performed the best cathodic protection capability for 304 stainless steel (304SS). In this case, the protective potential achieved −930 mV (versus SCE) associated with the photocurrent density of 475 μA/cm 2 , which was 14.8 times that of pure TiO 2 nanowires. In the dark, the nanocomposite provided cathodic protection of up to 485 mV for 304SS. Due to the heterogeneous junctions at the two interfaces among the three kinds of nanocomposite materials, the build-in electric field was fabricated, which promoted the separation efficiency of photogenerated electrons and holes and effectively improved the photochemical cathodic protection of 304SS. Proposed mechanism for the enhanced photoelectric activity of Ag@CuFe 2 O 4 @TiO 2 nanocomposite for photoelectric cathodic protection on 304SS under visible light illumination.

Crystal regulation of BiVO4 for efficient photocatalytic degradation in g-C3N4/BiVO4 heterojunction

The radicals generated by photocatalysis are widely used in environmental pollution treatment due to their super oxidizing ability and non-polluting characteristics, and are controlled through band potential and electron transfer types. Herein, through crystal engineering, we developed a novel g-C3N4/BiVO4 containing BiVO4 with different crystal structures, which can generate superoxide radicals and hydroxyl radicals under light irradiation. The (110) and (010) of BiVO4 crystal face showed different electron transfer paths, which proves that the existence of the build-in electric field is the internal driving force of S-scheme electron transfer. S-scheme electron transfer can reduce the recombination of electrons and holes, and promote the photocurrent density, and type Ⅱ electron transfer can reduce the decomposition of active oxides. By adjusting the ratio of S-scheme and type Ⅱ electron transfer, the addition of 1 % g-C3N4 could increase the photocatalytic activity of organic pollutants by 2.3 times. And the gap between the interfaces of g-C3N4 and BiVO4 also increases the adsorption capacity of pollutants. This research provides a theoretical basis for the regulation of the crystal structure and interface electron transfer in photocatalysis.

Substrate depended chemical composition segregation and electrical property of perovskite films

Morphology and chemical composition of the CH3NH3PbI3 films on bare glass and indium tin oxide (ITO) are investigated. The film on bare glass is smoother with a narrow grain size distribution, while the one on ITO is rougher with a large grain size distribution. Energy-dispersive X-ray and X-ray photoelectron spectra reveal that there is a superstoichiometric ratio of CH3NH3+ cations in the upper part of the CH3NH3PbI3 film deposited on ITO. Such a chemical composition segregation originates from the higher affinity of PbI2 to ITO. It is demonstrated that the CH3NH3+ cations can migrate to cathode under applied positive bias, which forms an ionic conductivity and increases the current of the device. Thus the device is in a high conductivity state. A large number of CH3NH3+ cations accumulated near the cathode forms a build-in electric field with a direction opposite to the external field. This restricts further migration of the CH3NH3+ cations and the device turns to a low conductivity state. The migration and accumulation of the CH3NH3+ cations manipulate the device to switch between the high and low conductivity states, endowing the device working as a memristor.

Enhanced photocatalytic activity of Z-scheme CeO2/CexBi2−xWO6 heterojunction induced by Ce doping and build-in electric field

Enhanced photocatalytic activity of Z-scheme CeO2/CexBi2−xWO6 heterojunction induced by Ce doping and build-in electric field

ZnO/MgZnO heterostructure membrane with type II band alignment for ceramic fuel cells

Semiconductor membrane fuel cells are a new promising R&amp;D for solid oxide fuel cells and proton ceramic fuel cells. There is a challenge of the electronic short circuit issue by using semiconductor to replace conventional electrolyte membrane. In this work, type II band alignment of the semiconductor heterostructure based on Mg-doped ZnO and ZnO can, on one hand, block electrons passing through the junction, and on the other hand, trigger the ionic properties of membrane to boost the fuel cell performance. The Mg doping into ZnO creates more oxygen vacancies at the surface of ZnO, leading to enhanced ionic transport, and meaningful fuel cell performance of 673 mW/cm2; while the Mg-doped ZnO/ZnO heterostructure fuel cell has delivered 997 mW/cm2 and OCV 1.04 V at 520 oC. It is worth highlighting that the constructed heterostructure interface, especially the band bending and constituted build-in electric field, plays a pivotal role in enhancing the ionic transport and suppressing the electron passing through the internal device. First principal calculations using density functional theory confirmed the doping of Mg and the formation of heterostructure with ZnO to help for enhancing charge carriers and separations. This work suggests that the constructed type II band alignment or the semiconductor heterostructure is useful for developing advanced fuel cells.

Dual Interfacial Build-In Electric Field Effect Induced by Sandwich-Type Heterojunction for Propelling Photocatalytic Fuel Extraction from Co2 in Water

Dual Interfacial Build-In Electric Field Effect Induced by Sandwich-Type Heterojunction for Propelling Photocatalytic Fuel Extraction from Co2 in Water

Fully-depleted dual P–N heterojunction with type-II band alignment and matched build-in electric field for high-efficient photocatalytic hydrogen production

In this work, a dual p-n heterojunction of Cu2O/Ni(OH)2/TiO2 with type-II band alignment and matched build-in electric field was fabricated. This dual p-n heterojunction promoted the separation and transfer of charge carriers, which is much more efficient than individual p-n heterojunction. Photocatalytic hydrogen evolution under the simulated sunlight shows a high rate of 6145 μmol g−1 h−1 for Cu2O/Ni(OH)2/TiO2, which is 1.9 and 2.7 times that of Ni(OH)2/TiO2 and Cu2O/TiO2, respectively. The apparent quantum yield of Cu2O/Ni(OH)2/TiO2 is about 20.2% under the irradiation of monochromatic light (λ = 420 nm). The recycling test of hydrogen evolution also verified a high stability for this dual heterojunction. The type-II band alignment and matched build-in electric field was confirmed, which accelerate the migration of charge carriers. The width of space-charge layer was calculated and proved that the p-n junctions in Cu2O/Ni(OH)2/TiO2 are fully-depleted, which largely reduced the bulk recombination of charge carriers. The synergistic effect of the improved visible-light response, type-II band alignment, matched build-in electric field, and fully-depleted space-charge layer contributes to the enhanced photocatalytic hydrogen evolution.