Single Heterojunction Research Articles

Simulation of CZTSSe single solar cells by AFORS-HET software

In this paper, this sthdy simulated photovoltaic characteristics of single heterojunction solar cell with Cu2ZnSnS4 and Cu2ZnSnSe4 absorber layer numerically using the AFORS-HET program .n-CdS/ZnO double buffer layer is used for hetrostructure interfaces with the absorber layer. The cell performance is investigated against variation of different absorption layer properties such as thickness, carrier concentration. The mixed zinc and cadmium sulphide (Cd1-X Zn X S) is hired as buffer layers and reseach of the effect its thickness. CdS was selected a buffer because it improves the interface with absorbent CZTSSe and has a lofty sending in the blue wavelength. at thickness =1 μm and acceptor concentration (Na=7.9×1015 cm-3) ,a maximum efficiency (η=11.9%) is provided with an open-circuit voltage (Voc=688mv), short-circuit current (Jsc=24.6 mA.cm-2) and fill factor (FF =70.8 of the CZTS solar cell, and Voc=(597 mv), Jsc= (41.7mA.cm-2), FF = (81.2 %) and η= (20.2%) of the CZTSe solar cell.

Highly Rectifying Heterojunctions Formed by Annealed ZnO Nanorods on GaN Substrates.

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.

Novel Boron-Doped p-Type Cu2O Thin Films as a Hole-Selective Contact in c-Si Solar Cells.

p-type Cu2O thin films doped with trivalent cation boron are demonstrated for the first time as an efficient hole-selective layer for c-Si heterojunction solar cells. Cu2O and Cu2O:B films were deposited by rf magnetron sputtering, and the optical and electrical properties of the doped and undoped films were investigated. Boron doping enhanced the carrier concentration and the electrical conductivity of the Cu2O film. The band alignment of the Cu2O:B/Si heterojunction was investigated using XPS and UPS measurements. The Cu2O:B/Si interface has a valance band offset of 0.08 eV, which facilitates hole transport, and a conduction band offset of 1.35 eV, which blocks the electrons. A thin SiOx tunnel oxide interlayer was also explored as the passivation layer. The initial trials of incorporating this Cu2O:B layer as a hole transporting layer in a single heterojunction solar cell with the structure, ITO/Cu2O:B/n-Si/Ag, and a cell area of 1 cm2 yielded an open-circuit voltage of 370 mV, a short-circuit current density of 36.5 mA/cm2, and an efficiency of 5.4%. This p-type material could find potential applications in various optoelectronic applications like organic solar cells, TFTs, and LEDs.

GeSn/GeSiSn double-heterojunction short channel tunnel field-effect transistor design

The traditional GeSn/GeSiSn single-heterojunction (SH) n-channel tunneling field-effect transistor (NTFET) faces a serious off-state current (IOFF) breakdown and a subthreshold swing (SS) degradation when the channel length is scaled to 10 nm. In this work, we propose a double-heterojunction (DH) short channel NTFET by utilizing heterojunction engineering. A 60% lower IOFF value (4.83 × 10−10 A μm−1), a 6.2 times higher ION value (9.39 × 10−6 A μm−1) and an SS of 39.14 mV/dec are achieved in the DH NTFET at 0.3 V compared to the SH NTFET when the channel length is 10 nm.

Sputter deposited p-NiO/n-SnO2 porous thin film heterojunction based NO2 sensor with high selectivity and fast response

In this work, we report fabrication and characterization of porous, single layer n-SnO2, p-NiO and bilayer thin film heterojunction devices developed using pulsed DC magnetron sputtering for NO2 detection. Template-free, NiO/SnO2 heterojunction devices were deposited both in top-bottom and in-plane electrode configurations. All the devices showed an optimum sensing temperature of 200 °C. Systematic comparison of the fabricated devices revealed that the heterojunction devices with top-bottom electrodes improved performance. Electrical characterization confirmed the formation of heterojunction across the interface. The response values of the heterojunction sensor ranged from 57 to 144 % for the NO2 concentration range of 2–10 ppm. The heterojunction device showed high selectivity against CO and NH3 with selectivity coefficients of 90 and 26, respectively. The heterojunction sensor exhibited fast response and recovery times of 37 and 98 s, respectively. The device showed excellent stability with < 2 % variation in response for 10 cycles of transient response characteristics. The I–V characteristics of heterojunctions with top-bottom and in-plane electrodes were explained by an equivalent circuit model. The observed enhancement in various parameters can be ascribed to the formation of distributed p-n nano-heterojunctions across the interface. The developed NiO/SnO2 heterojunction sensor by the simple and reproducible sputtering technique is found to be a promising candidate for the detection of NO2.

Alloy-like ternary polymer solar cells with over 17.2% efficiency

Ternary strategy has been considered as an efficient method to achieve high performance polymer solar cells (PSCs). A power conversion efficiency (PCE) of 17.22% is achieved in the optimized ternary PSCs with 10 wt% MF1 in acceptors. The over 8% PCE improvement by employing ternary strategy is attributed to the simultaneously increased JSC of 25.68 mA cm−2, VOC of 0.853 V and FF of 78.61% compared with Y6 based binary PSCs. The good compatibility of MF1 and Y6 can be confirmed from Raman mapping, contact angle, cyclic voltammetry and morphology, which is the prerequisite to form alloy-like state. Electron mobility in ternary active layers strongly depends on MF1 content in acceptors due to the different lowest unoccupied molecular orbital (LUMO) levels of Y6 and MF1, which can well explain the wave-like varied FF of ternary PSCs. The third-party certified PCE of 16.8% should be one of the highest values for single bulk heterojunction PSCs. This work provides sufficient references for selecting materials to achieve efficient ternary PSCs.

Demonstration of a Dual-Band InAs/GaSb Type-II Superlattice Infrared Detector Based on a Single Heterojunction Diode

We propose and demonstrate a new single heterojunction structure for dual-band detection based on type-II InAs/GaSb superlattices grown by metal-organic chemical vapor deposition. The structure simply consists of a p-type mid-wavelength contact layer, an n-type mid-wavelength absorber and an n-type long-wavelength absorber. At a small reverse bias, the presence of a potential barrier in the valence band between the two adjacent absorbers allows the mid-wavelength channel to work only; at a higher bias where the potential barrier no longer exists, photo-generated holes in the long-wavelength absorber are able to transport through the mid-wavelength absorber and reach the p-contact, making both channels to work. At −0.1 V and 77 K, the mid-wavelength channel exhibited a 50% cut-off wavelength of 3.5 $\mu \text{m}$ , a dark current density of $2.4\times 10^{{-9}}$ A/cm2, and a peak specific detectivity of $1.4\times 10^{{13}}$ cm $\cdot $ Hz1/2/W; while at −0.3 V the long-wavelength channel exhibited a 50% cut-off wavelength of 8.0 $\mu \text{m}$ , a dark current density of $5.1\times 10^{-7}$ A/cm2, and a peak specific detectivity of $3.6\times 10^{12}$ cm $\cdot $ Hz1/2/W.

Microstructural and Optical Characterization of Heterostructures of ZnS/CdS and CdS/ZnS Synthesized by Chemical Bath Deposition Method

ZnS/glass and CdS/glass single layers and ZnS/CdS and CdS/ZnS heterojunction thin films were deposited by the chemical bath deposition method using zinc acetate and cadmium acetate as the metal ion sources and thioacetamide as a nonmetallic ion source in acidic medium. Na2EDTA was used as a complexing agent to control the free cation concentration. The single layer and heterojunction thin films were characterized with X‐ray diffraction (XRD), a scanning electron microscope (SEM), energy dispersive X‐ray (EDX), and a UV‐VIS spectrometer. The XRD patterns of the CdS/glass thin film deposited on the soda lime glass substrate crystalized in the cubic structure with a single peak along the (111) plane. The ZnS/CdS heterojunction and ZnS/glass single layer thin films were crystalized in the hexagonal ZnS structure. The CdS/ZnS heterojunction thin film is nearly amorphous. The optical analysis results confirmed single band gap values of 2.75 eV and 2.5 eV for ZnS/CdS and CdS/ZnS heterojunction thin films, respectively. The CdS/glass and CdS/ZnS thin films have more imaginary dielectric components than the real part. The optical conductivity of the single layer and heterojunction films is in the order of 1015 1/s. The optical study also confirmed refractive index values between 2 and 2.7 for ZnS/glass, ZnS/CdS, and CdS/ZnS thin films for incident photon energies between 1.2 eV and 3.8 eV. The surface morphology studies revealed compacted spherical grains covering the substrate surfaces with few cracks on ZnS/glass, ZnS/CdS, and CdS/glass and voids on CdS/ZnS thin films. The EDX result confirmed nearly 1 : 1 metallic to nonmetallic ion ratio in the single‐layered thin films and the dominance of Zn ion over Cd ion in both ZnS/CdS and CdS/ZnS heterojunction thin films.

Performance Analysis of Double Gate Hetero Junction Tunnel Fet

In this paper, a novel heterojunction tunnel field-effect transistor (HTFET) using Sentaurus technology computer-aided design (TCAD) simulations has been presented. The InAs/GaSb compound materials are used in both single gate heterojunction TFET (SG-HTFET) and Double gate heterojunction TFET (DG-HTFET) with SiO2 gate oxide layer to increase performance of the device.The implemented SG-HTFET and DG-HTFET device are increase the TFET's cross-sectional tunnel area. This result develops the subthreshold swing (SS) by 2.45 times, drive current (ION) is close to 10-6 A/µm, leakage current (IOFF) is close to 10-17 A/µm and also diminish the ambipolarity of the device compared to the TFET.

Degradation mechanism of flexible perovskite solar cells: Investigated by tracking of the heterojunction property

Flexible perovskite solar cells (F-PSCs) with impressive power conversion efficiency (PCE) of 13.4 % were achieved on ITO/PEN substrate, where the high quality perovskite light harvesting layer with the composition of Cs0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3 was achieved by the well-established anti-solvent spin-coating method in our group. The unencapsulated F-PSCs can maintain 80 % of its initial value after 150 days exposed to ambient environment, the outstanding stability was among the best shelf stability ever reported for F-PSCs. Remarkably, a model based on the single heterojunction thin film solar cell was employed to clarify the irreversible degradation mechanism of the F-PSCs based on the evolution of the essential parameters during the aging process, like the ideality factor (A), series resistance (Rs) and the reverse saturated current density (J0). Our findings shed deep insight into the degradation mechanism of F-PSCs, and favorable for rational optimizing both the efficiency and stability of perovskite-based optoelectric device.

Modeling and analysis for the effects of gamma irradiation on the DC and AC performance in InGaP/GaAs SHBTs

ABSTRACTThe effects of gamma irradiation on the DC and AC characteristics of InGaP/GaAs single heterojunction bipolar transistors (SHBTs) are investigated comprehensively for the first time, which is based on experimental data before irradiation, after irradiation and after annealing. A simplified VBIC device model is developed to describe the DC and AC characteristics of the devices. The model parameters are extracted from experimental data before irradiation, after irradiation and after annealing. Finally, the degraded rates of model parameters are used to study the radiation-induced degradation of the device performance.

How does technological parameters impact the static current gain of InP-based Single Heterojunction Bipolar Transistor?

&lt;p&gt;In telecommunication systems, Heterojunction Bipolar Transistors (HBTs) are used extensively due to their good electrical characteristics. The work presented in this paper aims to enhance the electrical performance of the InP / InGaAs Single Heterojunction Bipolar Transistor (SHBT) in terms of the static current gain β. Silvaco’s TCAD tools were used for the simulation of the output characteristics of the studied electronic device. Initially, we used the interactive tool Deckbuild to define the simulation program and the device editor DevEdit to design the device structure, and we also used the simulator Atlas which allows the prediction of the electrical characteristics of most semiconductor devices. Because of several phenomena occuring within the electronic device SHBT, we added some physical models included in the simulator such as SRH, BBT.STD. Afterwards, we investigated the influence of doping concentrations of the base and the collector N&lt;sub&gt;b&lt;/sub&gt; and N&lt;sub&gt;c&lt;/sub&gt; on the electrical performance of the InP/InGaAs SHBT, and particularly in terms of the static current gain β. Finally, based on optimal values of the selected parameters, we have defined an optimized device that has a highest current gain β.&lt;/p&gt;

ZnO/ZnFe2O4/Ag hollow nanofibers with multicomponent heterojunctions for highly efficient photocatalytic water pollutants removal

Novel ZnO/ZnFe2O4/Ag hollow one-dimensional multicomponent heterojunctions with different ZnO/ZnFe2O4 ratios were successfully obtained via a simple electrospinning method. These multicomponent heterojunctions exhibited a largely enhanced photocatalytic performance for various reactions compared with pure ZnFe2O4 without heterojunctions, ZnO/ZnFe2O4 and ZnFe2O4/Ag with single heterojunctions. The enhancement can be mainly ascribed to the synergism of multicomponent heterojunctions, which can significantly improve the optical absorption abilities, prompt the separation of photogenerated carriers, and depress the recombination of electron-hole pairs. Hence, the simultaneous and efficient generation of electrons and holes with strong reduction and oxidation abilities, respectively, can lead to effective reaction with the target degradants. In addition, the unique hollow nanofiber structure can also prompt the activities by decreasing the distance for charge carrier transfer to the solution during the photocatalytic process. Additionally, the influence of the number of heterojunctions on the photoactivity was also discussed via varying the ZnO loading amount. This work displays an ingenious design to elevate photocatalytic performances of spinel ZnFe2O4 for solving its biggest problems in the photocatalytic applications, and reveals the rational design of photocatalysts for efficient water pollutants removal.

(Invited) Multiple Heterojunction in Single Titanium Dioxide Nanomaterials for Photocatalysis and Photoelectrochemical Cells

Despite a longstanding controversy surrounding TiO2 materials, TiO2 polymorphs with heterojunctions composed of anatase and rutile outperform individual polymorphs because of the type-II energetic band alignment at the heterojunction interface. Improvement in photocatalysis has also been achieved via black TiO2 with a thin disorder layer surrounding ordered TiO2. However, localization of this disorder layer in a conventional single TiO2 nanoparticle with the heterojunction composed of anatase and rutile has remained a big challenge. Here we report the selective positioning of a disorder layer of controlled thicknesses between the anatase and rutile phases by a conceptually different synthetic route to access highly efficient novel metal-free photocatalysis for H2 production. The presence of localized disorder layer within a single TiO2 nanoparticle was confirmed for the first time by high-resolution transmission electron microscopy (TEM) with electron energy-loss spectroscopy (EELS) and inline electron holography. Multiple heterojunctions in single TiO2 nanoparticles composed of crystalline anatase/disordered rutile/ordered rutile layers give the nanoparticles superior electron/hole separation efficiency and novel metal-free surface reactivity, which concomitantly yields an H2 production rate that is ~11 times higher than that of Pt decorated conventional anatase and rutile single heterojunction TiO2 systems.

Sesame: A 2-dimensional solar cell modeling tool

This work introduces a new software package “Sesame” for the numerical computation of classical semiconductor equations. It supports 1 and 2-dimensional systems and provides tools to easily implement extended defects such as grain boundaries or sample surfaces. Sesame is designed to facilitate fast exploration of the system parameter space and to visualize local charge transport properties. Sesame has been benchmarked against other software packages, and results for single crystal and polycrystalline CdS-CdTe heterojunctions are presented. Sesame is distributed as a Python package or as a standalone GUI application, and is available at https://pages.nist.gov/sesame/.

Design Analysis of Heterojunction Solar Cells with Aligned AZO Nanorods Embedded in p-type Si wafer

Higher price-per-watt of silicon (Si) solar cells is still the main bottleneck in their widespread use for power generation due to their expensive manufacturing process. The n-type zinc oxide (n-ZnO) and p-type Si (p-Si) based single heterojunction solar cell is one of the several methods being tried to replace conventional Si single homojunction solar cell technology. In this work, we have explored the possibility of producing photovoltaic materials by employing RF sputtering and hydrothermal technologies. Conductivity of ZnO nanorods has been increased by aluminium (Al) doping. The advantages of using Al doped ZnO (AZO) nanorods (NRs) have been investigated. The integrated reflectance (IR) has been found to be only ~2.86%. Hence, the short circuit current density (Jsc) has been increased by minimizing the reflection loss of solar cells. AZO NR array have been developed over several large area (3″ × 3″) textured p-Si wafers to confirm the repeatability. The maximum efficiency of AZO NRs/Si solar cell of 0.8 cm2 area has been found to be 6.25% for textured p-type Si wafer which is much higher than reported hitherto for this type of solar cell. A simple, low temperature, low cost procedure is thus being proposed, which has the potential of attaining lower cost of production of heterojunction silicon solar cells.

1D ZnSSe‐ZnSe Axial Heterostructure and its Application for Photodetectors

AbstractSemiconductor heterostructure nanowires (HNWs) are excellent candidates for application in compact optoelectronics devices with high performance due to the heterojunction interface effect. However, the controllable fabrication of high‐quality nano‐heterostructures is elusive. In this paper, the controllable growth and optoelectronics device application of high‐quality ZnS0.49Se0.51/ZnSe axial HNWs are reported. The as‐synthesized HNWs are straight with uniform diameter distribution of 50–100 nm. Microstructural characterization reveals single crystal and abrupt heterojunction interface in these HNWs. The micro‐photoluminescence of single component region and heterojunction zone show one and integrated two near bandgap emission of ZnS0.49Se0.51 and ZnSe, respectively, further demonstrating the abrupt heterojunction interfaces nature in the as‐grown nanowires. Moreover, photodetectors based on single HNW are fabricated and the responsivity, external quantum efficiency, response speed, and detection wavelength range are superior to that of single component nanowire photodetectors at room temperature. These results show that the ZnS0.49Se0.51/ZnSe HNWs and corresponding high‐performance photodetectors are prospective candidates for photonics and optoelectronics applications.

Investigation of the static current gain for InP/InGaAs single heterojunction bipolar transistor

&lt;p&gt;Heterojunction Bipolar Transistors are being used increasingly in communication systems due to their electrical performances. They are considered as excellent electronic devices. This paper presents an investigation of the static current gain β based on two technological parameters related to the device geometry for InP/InGaAs Single Heterojunction Bipolar Transistor (SHBT). These parameters are the base width and the emitter length . We used Silvaco’s TCAD tools to design the device structure, and to extract the static current gain β from I-V output characteristics figures. According to this investigation, we determined the optimal values of the examined parameters which allow obtaining the highest static current gain β.&lt;/p&gt;

Electron Affinity and Bandgap Optimization of Zinc Oxide for Improved Performance of ZnO/Si Heterojunction Solar Cell Using PC1D Simulations

For further uptake in the solar cell industry, n-ZnO/p-Si single heterojunction solar cell has attracted much attention of the research community in recent years. This paper reports the influence of bandgap and/or electron affinity tuning of zinc oxide on the performance of n-ZnO/p-Si single heterojunction photovoltaic cell using PC1D simulations. The simulation results reveal that the open circuit voltage and fill factor can be improved significantly by optimizing valence-band and conduction-band off-sets by engineering the bandgap and electron affinity of zinc oxide. An overall conversion efficiency of more than 20.3% can be achieved without additional cost or any change in device structure. It has been found that the improvement in efficiency is mainly due to reduction in conduction band offset that has a significant influence on minority carrier current.

Dry-pressed anodized titania nanotube/CH3NH3PbI3 single crystal heterojunctions: The beneficial role of N doping

Highly ordered, anodically grown TiO2 nanotubes on titanium supports were annealed in ammonia atmosphere in order to incorporate nitrogen doping (≤2 at.%) in the titanium oxide lattice. FESEM micrographs revealed nanotubes with an average outer diameter of 101.5 ± 1.5 nm and an average wall thickness of about 13 nm. Anatase crystals were formed inside the tubes after annealing in ammonia atmosphere for 30 min. With further annealing, rutile peaks appeared due to the thermal oxidation of the foil and rise as the duration of heat treatment was increased. The concentration and chemical nature of nitrogen in the nanotube arrays can be correlated to the optical response of dry-pressed heterojunctions of doped TiO2/CH3NH3PbI3 single crystals. The N-TiO2/perovskite heterojunction with the highest amount of interstitial nitrogen exhibited an improved photocurrent, indicating the importance of the semiconductor doping-based heterojunction optimization strategies to deliver competitive levels of halide perovskite-based optoelectronic devices to be envisioned for urban infrastructures.