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Transconductance Amplification in Dirac-Source Field-Effect Transistors Enabled by Graphene/Nanotube Hereojunctions
摘要： Steep-slope devices are predicted to provide excellent quality for analog integrated circuit applications due to their high transconductance efficiency (gm/Ids) breaking the metal-oxide-semiconductor field-effect transistor limit (38.5 V?1). The potential advantage of a Dirac-source FET (DSFET) as an analog transistor is explored based on a graphene/carbon nanotube (CNT) heterojunction. A high gm/Ids beyond 38.5 V?1 over four decades of current is experimentally demonstrated in an individual CNT-based DSFET, reaching a peak value of 66 V?1, which is a new record for all reported transistors. Importantly, this high gm/Ids extends beyond the subthreshold region and leads to transconductance amplification in the overthreshold region. The best peak transconductance at a low bias of ?0.1 V exceeds 20 μS per tube, which has approximately threefold improvement over that of a normal CNT FET with a shorter gate length. Outperforming other advanced devices, the extended high transconductance efficiency greatly promotes DSFET competitiveness in the high-precision analog field.
关键词： carbon nanotubes,heterojunctions,Dirac sources,graphene,field-effect transistors
更新于2025-09-23 15:21:01
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Reduced graphene oxide hybridized with WS2 nanoflakes based heterojunctions for selective ammonia sensors at room temperature
摘要： Hybrid of the two dimensional nanostructured reduced graphene oxide (rGO) and WS2 has been investigated for a room temperature ammonia sensor. The formed rGO/WS2 heterojunctions prepared by one-step hydrothermal synthesis indicated a good sensitivity to different concentrations of ammonia from 10 ppm to 50 ppm at room temperature. The WS2 nanoflakes doped in the heterojunction plays significant role in the enhanced response through the introduction of more hydroxyls in rGO and the extra Lewis acid active centers. The sensor also shows an excellent selectivity to NO2, alcohols, formaldehyde，acetone and benzene and a good long term stability indicating a potential to be employed as a room temperature NH3 sensor.
关键词： rGO/WS2 heterojunctions,Room Temperature,Ammonia Sensors
更新于2025-09-23 15:21:01
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Spontaneously Selfa??Assembly of a 2D/3D Heterostructure Enhances the Efficiency and Stability in Printed Perovskite Solar Cells
摘要： As perovskite solar cells (PSCs) are highly efficient, demonstration of high-performance printed devices becomes important. 2D/3D heterostructures have recently emerged as an attractive way to relieving the film inhomogeneity and instability in perovskite devices. In this work, a 2D/3D ensemble with 2D perovskites self-assembled atop 3D methylammonium lead triiodide (MAPbI3) via a one-step printing process is shown. A clean and flat interface is observed in the 2D/3D bilayer heterostructure for the first time. The 2D perovskite capping layer significantly suppresses nonradiative charge recombination, resulting in a marked increase in open-circuit voltage (VOC) of the devices by up to 100 mV. An ultrahigh VOC of 1.20 V is achieved for MAPbI3 PSCs, corresponding to 91% of the Shockley–Queisser limit. Moreover, notable enhancement in light, thermal, and moisture stability is obtained as a result of the protective barrier of the 2D perovskites. These results suggest a viable approach for scalable fabrication of highly efficient perovskite solar cells with enhanced environmental stability.
关键词： stability,2D/3D heterojunctions,self-assembly,perovskite solar cells,high efficiency
更新于2025-09-23 15:19:57
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Precession Electron Diffraction and Orientation Phase Mapping of Assembled Ag/ZnO Nanoantennas
摘要： The manipulation of the geometrical and structural arrangement of the constituent’s elements on devices at nanoscale level is highly desirable for a precise monitoring of the opto-electrical properties exhibited for these nanomaterials. In fact, a great effort has being made to understand the coupling mechanisms on metal-semiconductors systems, most precisely at interfaces nanoscale level. For instance, it is well known that the multidirectional radiation pattern generated by the active elements on nanoantenna applications is highly dependent on both the structural and orientation distribution of the receiver elements as well as the passive element on the nanoscale device. For example, Wang, et al [1] have synthesized high order nanostructures in a hierarchical configuration to study the photo-induced optical properties of these systems in function of the ZnO concentration distributed along the silver nanowires. However, few is known about the structural coupling mechanisms between this metal-semiconductor heterojunctions. Thus, to understand the dynamic coupling at the interface level in the Ag/ZnO metal-semiconductor heterojunctions we report the epitaxial growing of zinc oxide nanorods on the pentagonal exposes faces of Ag nanowires resembling a hierarchal nanoantenna. Moreover, the studied of the growth mechanism in the active/contact faces of the metal-semiconductor heterojunction has been done by mapping simultaneously the dynamical electron diffraction pattern under in-situ precession electron diffraction at the heterojunction interface Ag/ ZnO nanosystem. Indeed, by indexing the dynamical diffraction patterns using orientational/phase mapping from the precessed electron diffraction data collected an orientational mapping has been retrieved showing the interfacial growing polar planes (0002) of ZnO nanorods on the pentagonal planes of silver nanowires with a mismatch between planes along the coupling interface. For completeness, grazing angle x-ray diffraction measurements on prepared substrates Ag/ZnO systems shown well-defined peaks associated to the main phases of ZnO nanorods and Ag nanowires respectively. A full understanding of the fit faces mechanism between Ag/ZnO along the mismatch direction undoubtedly will allow elucidating the mechanism through which the contact metal-semiconductor behaves at the heterojunction interface.
关键词： Nanoscale Devices,Ag/ZnO Nanoantennas,Metal-Semiconductor Heterojunctions,Orientation Phase Mapping,Precession Electron Diffraction
更新于2025-09-23 15:19:57
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Direct Silicon Heterostructures With Methylammonium Lead Iodide Perovskite for Photovoltaic Applications
摘要： We investigated the formation of photovoltaic (PV) devices using direct n-Si/MAPI (methylammonium lead tri-iodide) two-sided heterojunctions for the first time (as a possible alternative to two-terminal tandem devices) in which charge might be generated and collected from both the Si and MAPI. Test structures were used to establish that the n-Si/MAPI junction was photoactive and that spiro-OMeTAD acted as a “pinhole blocking” layer in n-Si/MAPI devices. Two-terminal “substrate” geometry devices comprising Al/n-Si/MAPI/spiro-OMeTAD/Au were fabricated and the effects of changing the thickness of the semitransparent gold electrode and the silicon resistivity were investigated. External quantum efficiency and capacitance–voltage measurements determined that the junction was one-sided in the silicon—and that the majority of the photocurrent was generated in the silicon, with there being a sharp cutoff in photoresponse above the MAPI bandgap. Construction of band diagrams indicated the presence of an upward valence band spike of up to 0.5 eV at the n-Si/MAPI interface that could impede carrier flow. Evidence for hole accumulation at this feature was seen in both Kelvin-probe transients and from unusual features in both current–voltage and capacitance–voltage measurements. The devices achieved a hysteresis-free best power conversion efficiency of 2.08%, VOC 0.46 V, JSC 11.77 mA/cm2, and FF 38.4%, demonstrating for the first time that it is possible to create a heterojunction PV device directly between the MAPI and n-Si. Further prospects for two-sided n-Si/MAPI heterojunctions are also discussed.
关键词： heterostructures,MAPI/silicon methylammonium lead iodide,methylammonium lead tri-iodide (MAPI),Heterojunctions,silicon
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Reciprocal relationship between photoluminescence and photocurrent in two-step photon up-conversion solar cell
摘要： Two-step photon up-conversion solar cell (TPU-SC) we have recently proposed is a single-junction solar cell containing a hetero-interface of different semiconductor materials. Although efficient two-step photon up-conversion is achieved in the TPU-SC, the detailed mechanism of intraband photoexcitation occurring at the hetero-interface is still unclear. In this study, we performed simultaneous measurements of photoluminescence and photocurrent as a function of the applying bias voltage in the TPU-SC. We experimentally demonstrate the reciprocity relationship between the radiative recombination and the photocurrent of the TPU-SC.
关键词： photovoltaic cells,gallium arsenide,quantum dots,heterojunctions,radiative recombination,photoluminescence
更新于2025-09-23 15:19:57
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Highly Rectifying Heterojunctions Formed by Annealed ZnO Nanorods on GaN Substrates
摘要： We study the effect of thermal annealing on the electrical properties of the nanoscale p-n heterojunctions based on single n-type ZnO nanorods on p-type GaN substrates. The ZnO nanorods are prepared by chemical bath deposition on both plain GaN substrates and on the substrates locally patterned by focused ion beam lithography. Electrical properties of single nanorod heterojunctions are measured with a nanoprobe in the vacuum chamber of a scanning electron microscope. The focused ion beam lithography provides a uniform nucleation of ZnO, which results in a uniform growth of ZnO nanorods. The specific configuration of the interface between the ZnO nanorods and GaN substrate created by the focused ion beam suppresses the surface leakage current and improves the current-voltage characteristics. Further improvement of the electrical characteristics is achieved by annealing of the structures in nitrogen, which limits the defect-mediated leakage current and increases the carrier injection efficiency.
关键词： chemical bath deposition,nanoscale heterojunctions,ZnO nanorods,nanoprobe in the scanning electron microscope,current-voltage characteristics,annealing,focused ion beam patterning
更新于2025-09-23 15:19:57
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Significantly Enhanced Molecular Stacking in Ternary Bulk Heterojunctions Enabled by an Appropriate Side Group on Donor Polymer
摘要： Ternary strategy is a promising approach to broaden the photoresponse of polymer solar cells (PSCs) by adopting combinatory photoactive blends. However, it could lead to a more complicated situation in manipulating the bulk morphology. Achieving an ideal morphology that enhances the charge transport and light absorption simultaneously is an essential avenue to promote the device performance. Herein, two polymers with different lengths of side groups (P1 is based on phenyl side group and P2 is based on biphenyl side group) are adopted in the dual-acceptor ternary systems to evaluate the relationship between conjugated side group and crystalline behavior in the ternary system. The P1 ternary system delivers a greatly improved power conversion efficiency (PCE) of 13.06%, which could be attributed to the intense and broad photoresponse and improved charge transport originating from the improved crystallinity. Inversely, the P2 ternary device only exhibits a poor PCE of 8.97%, where the decreased device performance could mainly be ascribed to the disturbed molecular stacking of the components originating from the overlong conjugated side group. The results demonstrate a conjugated side group could greatly determine the device performance by tuning the crystallinity of components in ternary systems.
关键词： ternary systems,ternary bulk heterojunctions,complementary absorption,polymer solar cells,molecular stacking,side chain effect
更新于2025-09-23 15:19:57
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Improved photovoltaic performance of graphene-based solar cells on textured silicon substrate
摘要： Graphene has attracted much interest as an active layer in heterojunction solar cells due to its outstanding properties such as flexibility, transparency, mechanical strength and elevated carrier mobility. In this research, a new technique was presented in order to enhance the efficiency of graphene–based heterojunction solar cells by employing a textured silicon (Si) substrate. Here, two sets of devices were fabricated based on flat and pyramidal structure of Si and the photovoltaic properties of graphene/Si heterojunction solar cells were compared. Selective chemical dissolution of Si wafers was carried out in order to produce pyramidal skeleton. Reduced graphene oxide (rGO) was then transferred on pyramidal Si through electrophoretic deposition (EPD) technique. The evidence of graphene layers on Si substrates was studied using Raman spectroscopy, X–ray diffractometry (XRD) and atomic force microscopy (AFM) analysis. The morphology of samples indicated an enhancement in rGO/Si interface area when the pyramidal structure is applied. Moreover, the enhanced surface area of this sample which is due to elevated roughness of pyramidal structure and wrinkles of graphene layers promotes its antireflective behavior which was proven using reflectance spectroscopy. The average reflectance of the graphene layer on the textured Si was ~14% in the wavelength range of 400–800 nm which is lower than that of rGO on flat Si. The improved optical properties of graphene on pyramidal silicon can broaden its potential applications in optoelectrical devices such as high-efficiency solar cells. In order to study the photovoltaic properties of rGO/Si samples, a passive layer was formed on Si substrate and a square frame of Ag was coated on it which was acted as a top contact. The current–voltage characteristics showed that the efficiency of rGO/Si heterojunction solar cells was improved when textured silicon was applied.
关键词： Schottky junction solar cell,Heterojunctions,Thin films,Reduced graphene oxide,Silicon pyramids,Electrophoretic deposition
更新于2025-09-23 15:19:57
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Higha??Performance Pseudoplanar Heterojunction Ternary Organic Solar Cells with Nonfullerene Alloyed Acceptor
摘要： The vast majority of ternary organic solar cells are obtained by simply fabricating bulk heterojunction (BHJ) active layers. Due to the inappropriate distribution of donors and acceptors in the vertical direction, a new method by fabricating pseudoplanar heterojunction (PPHJ) ternary organic solar cells is proposed to better modulate the morphology of active layer. The pseudoplanar heterojunction ternary organic solar cells (P-ternary) are fabricated by a sequential solution treatment technique, in which the donor and acceptor mixture blends are sequentially spin-coated. As a consequence, a higher power conversion efficiency (PCE) of 14.2% is achieved with a Voc of 0.79 V, Jsc of 25.6 mA cm?2, and fill factor (FF) of 69.8% compared with the ternary BHJ system of 13.8%. At the same time, the alloyed acceptor is likely formed between two the acceptors through a series of in-depth explorations. This work suggests that nonfullerene alloyed acceptor may have great potential to realize effective P-ternary organic solar cells.
关键词： ternary organic solar cells,sequential spin-coating,pseudoplanar heterojunctions,nonfullerene alloyed acceptors
更新于2025-09-23 15:19:57