Additional Interfacial Layer Research Articles

Investigation of the effect of different back contacts on the growth and efficiency of cigs solar cells

Herein, 〖Cu(In〗_(1-x) Ga_(1-x))(〖S,Se)〗_2 films were successfully deposited onto different back contacts: fluorite tin oxide (ITO), Indium doped Tin Oxide (FTO), and Molybdenum Mo by spray pyrolysis technique. The effect of back contacts on the structural and optical properties of CIGS was investigated. The X-ray patterns reveal crystalline phases with preferred phase orientations (112), (220), (220/214), and (312/116) for the different samples and a (110) phase of MoS2, particularly for the molybdenum back contact. SEM showed good crystallinity of the deposit films, especially for CIGS deposited at FTO back contact shows less porosity, homogenous surface, and good crystal size. Optical analyses for different back contacts provided bandgaps of 1.2 eV, 1.4 eV, and 1.64 eV for the films deposited on Mo, FTO, and ITO, respectively. SCAPS-1D simulator was used to exhibit the electrical characteristics of each cell according to the CIGS-deposition results. Among the different back contacts used, Mo showed the best efficiency of 22.93%. For FTO and ITO back contacts, the additional interfacial layer (MoS2 or MoSe2) between the absorber and the back contact shows an improvement in the efficiency from 22.59% to 23,97% and from 13.8% to 14.05%, respectively.

Defect Passivation by a Donor–Acceptor–Donor‐Structured Small Molecule via Bidentate Anchoring for Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) have exhibited a tremendous photovoltaic performance over the past few years. However, the ionic nature of perovskite and the solution‐processable fabrication methods lead to various defects (vacancies, interstitials, and antisites) at the perovskite surface. Incorporating interfacial or surface passivation layers has proved to be crucial in passivating these defects. Herein, a novel donor–acceptor–donor (D–A–D)‐based bidentate material, namely, BDTBT, consisting of benzothiadiazole (BDT) as the central acceptor unit and benzothiophene (BT) as a donor end cap unit, is synthesized. The various structural analyses reveal that N and S heteroatoms at BDTBT coordinate effectively to undercoordinated Pb2+in perovskite via Pb–N/S bidentate interactions. As a result, the BDTBT‐treated perovskite exhibits an improved power conversion efficiency (PCE) of 20.42% compared with the bare perovskite, having a PCE of 17.18%. The BDTBT incorporation provides favorable band alignment, increased hole transfer, and suppressed nonradiative recombination losses by reducing the surface defect states. In addition, there is significant increase in the device stability and moisture resistance owing to the hydrophobic nature of BDTBT. This study provides a simple and efficient route to obtain stable and highly efficient PSCs by incorporating small molecules as an additional interfacial layer.

Fabrication and testing of Mg2Si1-xSnx based thermoelectric generator module

Mg2Si1-xSnx solid solutions have been of great interest for the advantages they hold as prospective thermoelectric (TE) materials. Despite this, the development of thermoelectric generator (TEG) modules fabricated entirely from these materials has not been reported. In this work, a TEG module consisting of Mg2Si0.3Sn0.7n and p legs has been fabricated, and its thermoelectric generator characteristics were studied as a function of the applied temperature gradient. For the n and p doped legs, compositions with peak zT values of ~1.6 and ~0.44, respectively, were synthesized using induction assisted melt synthesis. Mono-block sintering technique was adopted as a single-step compaction cum contacting technique. In order to create low resistive well-bonded contacts, an additional interfacial layer was placed between the TE material and the outer Cu layer. The TE legs were assembled into a skeletal module comprising of two unicouples electrically connected by Cu bridges. The transient state I-V characteristics of the TE device were measured at various temperature gradients (ΔT). A maximum power output value of 192mW (corresponds to a power density of 0.52 W/cm2) and open-circuit voltage of 200 mV were measured for a ΔT of 331 K. The measured I-V and power output data showed good agreement with the simulated power output values with a variation of only 3% until ΔT = 300 K and 5% at ΔT = 331 K. The TE module simulator was further used to estimate the device efficiency (η) and indicated a maximum value of 5%. This is the highest reported conversion efficiency of a silicide based module (in the studied temperature range) and highlights the possibility of their commercialization in the near future.

Enhanced surface passivation with TIPS pentacene and additional interfacial layer for MIS solar cells

Enhanced surface passivation with TIPS pentacene and additional interfacial layer for MIS solar cells

Adjusting Interfacial Chemistry and Electronic Properties of Photovoltaics Based on a Highly Pure Sb2S3 Absorber by Atomic Layer Deposition.

The combination of oxide and heavier chalcogenide layers in thin film photovoltaics suffers limitations associated with oxygen incorporation and sulfur deficiency in the chalcogenide layer or with a chemical incompatibility which results in dewetting issues and defect states at the interface. Here, we establish atomic layer deposition (ALD) as a tool to overcome these limitations. ALD allows one to obtain highly pure Sb2S3 light absorber layers, and we exploit this technique to generate an additional interfacial layer consisting of 1.5 nm ZnS. This ultrathin layer simultaneously resolves dewetting and passivates defect states at the interface. We demonstrate via transient absorption spectroscopy that interfacial electron recombination is one order of magnitude slower at the ZnS-engineered interface than hole recombination at the Sb2S3/P3HT interface. The comparison of solar cells with and without oxide incorporation in Sb2S3, with and without the ultrathin ZnS interlayer, and with systematically varied Sb2S3 thickness provides a complete picture of the physical processes at work in the devices.

Double Interfacial Layers Effect on Optical Third-order Nonlinear Susceptibility, Refraction Index, and Absorption Coefficient of a Metal/ Dielectric Composite

We investigate the way of enhancing the optical third order susceptibility, the refractive index, and absorption coefficient of a composite media in which identical nonlinear nanospheres having double interfacial layer randomly embedded in the linear host medium. We observe two maxima peaks of the nonlinear properties. We also show that the effect of double interfacial layers on the third order susceptibility, the refractive index, and absorption coefficient depends on the volume fraction metal/ dielectric nanosphers and the nature of the double interfacial layers. Under appropriate condition (nature of the two interfacial layer) we found two maximum peaks of the nonlinear properties. We also compare with the same composite without interfacial layer and in the presence of single interfacial layer and our finding shows that because of additional interfacial layer the effective medium exhibit a better third-order susceptibility, refractive index, and absorption coefficient.

Effects of Double Interfacial Layers on the Local Field Enhancement Factor and Optical Induced Bistability of a Small Spherical Metal/Dielectric Composites

We propose the way of enhancing the enhancement factor of local field, and increasing the input domain threshold of the optical induced bistability of a spherical metal/dielectric composites within a linear host matrixes. The local field enhancement factor of a metal particles with dielectric core in the presence of double interfacial layers shows two maxima at two different frequencies. By introducing double interfacial layers, we calculate the enhancement factor of the local field. Also using the cubic equation the optical induced bistability of the composite material is calculated. Because of the double interfacial layers, we observe an increasing of the input domain threshold of the optical induced bistability. In comparison with the same composite without interfacial layer and with having single interfacial layer, our finding shows that, introducing additional interfacial layer makes the composite having a better enhancement factor and much better input domain threshold of the optical induced bistability.

Structure and stability of Gd-doped CeO2 thin films on yttria-stabilized zirconia

25nm thick Gd-doped ceria thin films were grown on yttria-stabilized zirconia (YSZ) substrates with (110) and (111) orientation by pulsed laser deposition to study both their crystalline structure and interfacial stability. The films were characterized by high-energy grazing incidence x-ray diffraction, x-ray reflectivity and x-ray photoelectron spectroscopy before and after annealing to 1400K under ultra-high vacuum (UHV) conditions. The films were found to be epitaxial to the YSZ substrates, exhibiting good crystalline quality without defects like twinning, and low surface roughness. Upon reduction due to the annealing in ultrahigh vacuum (UHV), both samples showed an increase in lattice parameter while maintaining their original crystalline quality. The x-ray reflectivity measurements gave evidence for interdiffusion after annealing by the presence of an additional interfacial layer with reduced electron density. X-ray photoelectron spectroscopy revealed an increase in the concentration of Ce3+ and also yttrium at the surface upon annealing, indicating a slight reduction of the surface as well as diffusion of yttrium to the surface.

Analysis of efficiently poled electro-optic polymer/Tio2 vertical slot waveguide modulators

We analyze the advantages of an electro-optic (EO) polymer/TiO2 vertical slot waveguide modulator based on a low-index EO polymer (SEO125). This modulator can realize a lower half-wave voltage (Vπ)-electrode length (Le) product (VπLe) when compared with hybrid EO polymer (EOP)/sol–gel silica waveguide modulators because of the high mode confinement of the guided light and the high poling efficiency. We show the enhancement of the poling efficiency in these devices when the EO polymers are poled with TiO2 and sol–gel silica layers. We also enhance the EO coefficient to a level of 260pm/V at a wavelength of 1.31μm for a high-index EOP (SEO100) deposited on TiO2, a sol–gel silica cladding layer, and an additional interfacial layer.

The Effect of Ni Interlayers on Compaction of Mo/Mo Silicide Composites

Abstract: Reactions during compaction of Mo/Mo silicide wires with Ni interlayers are qualitatively assessed in this work. It appeared that due to extreme high temperature strength of MoSi2 hot pressing even at 1800°C/60 min/30 MPa in vacuum had not been sufficient to compact the Mo/Mo silicide wires in the absence of any additional interfacial layer. Therefore Ni had been chemically coated on the surface of Mo/Mo silicide wires that were subsequently compacted by hot pressing. Structural analysis revealed the reaction between Ni and MoSi2 resulting in the formation of ternary (MoNiSi) compounds. These established an interfacial bonding with minimal porosity.

Equivalent oxide thickness scaling of Al2O3/Ge metal—oxide—semiconductor capacitors with ozone post oxidation

Aluminum—oxide films deposited as gate dielectrics on germanium (Ge) by atomic layer deposition were post oxidized in an ozone atmosphere. No additional interfacial layer was detected by the high-resolution cross-sectional transmission electron microscopy and X-ray photoelectron spectroscopy measurements made after the ozone post oxidation (OPO) treatment. Decreases in the equivalent oxide thickness of the OPO-treated Al2O3/Ge MOS capacitors were confirmed. Furthermore, a continuous decrease in the gate leakage current was achieved with increasing OPO treatment time. The results can be attributed to the film quality having been improved by the OPO treatment.

Influence of Carbon Layer on the Properties of Ni-Based Ohmic Contact to n-Type 4H-SiC

Nickel-based contacts with additional interfacial layer of carbon, deposited on n-type 4H-SiC, were annealed at temperatures ranging from 600 to 1000°C and the evolution of the electrical and structural properties were analyzed by I-V measurements, SIMS, TEM, and Raman spectroscopy. Ohmic contact is formed after annealing at 800°C and minimal specific contact resistance of about 2.0×10-4 Ω cm2 has been achieved after annealing at 1000°C. The interfacial carbon is amorphous in as-deposited state and rapidly diffuses and dissolves in nickel forming graphitized carbon. This process activates interfacial reaction between Ni and SiC at lower temperature than usual and causes the formation of ohmic contact at relatively low temperature. However, our results show that the specific contact resistance as well as interface quality of contacts was not improved, if additional layer of carbon is placed between Ni and SiC.

Self-healing sandwich structures incorporating an interfacial layer with vascular network

A self-healing capability specifically targeted for sandwich composite laminates based on interfacial layers with built-in vascular networks is presented. The self-healing occurs at the facesheet–core interface through an additional interfacial layer to seal facesheet cracks and rebond facesheet–core regions. The efficacy of introducing the self-healing system at the facesheet–core interface is evaluated through four-point bend and edgewise compression testing of representative foam core sandwich composite specimens with impact induced damage. The self-healing interfacial layer partially restored the specific initial stiffness, doubling the residual initial stiffness as compared to the control specimen after the impact event. The restoration of the ultimate specific skin strength was less successful. The results also highlight the critical challenge in self-healing of sandwich composites, which is to rebond facesheets which have separated from the core material.

SIMULATION OF CNT COMPOSITES USING FAST MULTIPOLE BEM

This paper addresses some applications of the fast multipole boundary element method on the simulation of CNT composites, including the simulation of elastic, thermal and electric properties. The carbon nanotubes are treated as effective elastic fibers for the simulation of elastic property, and treated as straight fibers with high thermal conductivity and high electric conductivity for the simulation of thermal and electric properties respectively. The numerical examples are compared with other numerical results and experimental data published in literature. To reduce the difference between numerical and experimental value of effective elastic modulus, two approaches with nonideal interfacial condition or additional interfacial layer have been introduced. Numerical tests clearly demonstrate the potential of the FM-BEM for large scale simulation of CNT composites.

Effects of Low-temperature NH3 Treatment on the Characteristics of HfO2 ∕ SiO2 Gate Stack

The effects of postdeposition low-temperature treatment (LTN treatment) on the characteristics of the gate stack with the TiN gate electrode were studied in this work. After the films were deposited using an AIXTRON Tricent atomic vapor deposition system, the LTN treatment was performed prior to the postdeposition annealing (PDA) step to prevent the growth of an additional interfacial layer, which is known to accompany the traditional high-temperature nitridation technique. The effective electrical oxide thickness for the devices annealed at 700°C PDA, either with or without LTN treatment, was estimated to be about 2.2 and 2.3 nm, respectively, without considering quantum effects. It was found that the LTN treatment effectively improves the characteristics of the stack gates, such as capacitance-voltage characteristics, frequency dispersion, trap generation rate, and dielectric breakdown voltage even at the high PDA temperature of 700°C.

Electrical characteristics of postdeposition annealed HfO2 on silicon

Electrical characteristics of ultrathin HfO2 films on p-type silicon (100) substrates were determined by capacitance-voltage and current density-voltage measurements. The as-deposited HfO2 films showed a dielectric constant of ∼22, a leakage current density of 5A∕cm2 and an interface state density of 6.5×1012cm2eV−1 at an equivalent oxide thickness (EOT) of 7.6Å due to the poor quality of HfO2∕Si interface. However, annealing in O2 and NH3 significantly reduced the interface state densities to 8.4×1011cm2eV−1 and 7.38×1011cm2eV−1, respectively, although the annealing increased the EOTs to 12.3Å and 11.3Å respectively, due to the growth of an additional interfacial layer. The forming gas anneal with either H2 or D2, however, significantly improved the quality of the HfO2∕Si interface without affecting the EOT. Postdeposition annealing in all chemistries decreased the leakage current densities by orders of magnitude at the same EOT compared to that of SiO2. The current transport mechanism in the as-deposed HfO2 sample is determined to be direct tunneling, and an Al∕HfO2 barrier height of 1.3eV and a HfO2∕Si barrier height of 1.4eV were obtained. The latter is in good agreement with the band offset determined by x-ray photoelectron spectroscopy analysis and ab initio calculations.

Al 2 O 3 / Si 3 N 4 stacked insulators for 0.1 μm gate metal–oxide–semiconductor transistors realized by high-density Si3N4 buffer layers

We developed Al2O3/Si3N4 stacked insulators suitable for the advanced metal–oxide–semiconductor (MOS) devices. Ultrathin Si3N4 was prepared by direct nitridation of Si substrate using atomic nitrogen radicals. With this process, the film obtained was less defective compared to conventional Si3N4. Al2O3 was then deposited by atomic layer deposition on Si3N4 and oxidized to eliminate defects in the film. Since the buffer Si3N4 does not contain a large amount of hydrogen, we could perform high-temperature oxidation without any additional interfacial layer formation in the Si substrate. We achieved high capacitance density and low leakage current that are acceptable for the gate insulator in advanced MOS devices with a 0.1 μm gate length by exploiting this buffering technique.

Physical and electrical degradation of ZrO 2 thin films with aluminum electrodes

Zirconium oxide thin films were deposited on p-type (1 0 0) silicon wafers by reactive d.c. magnetron sputtering. The as-deposited ZrO 2 films at the power of 300 W and at room temperature were amorphous and the ZrO 2 films became polycrystalline with both the monoclinic and tetragonal phases after post-annealing at 450 °C in N 2 ambient. The ZrO 2 films with Al electrode had the interfacial amorphous Al–O-containing layer, which was formed by their interaction, but the films with inactive electrodes such as Pt had no additional interfacial layer. The value of the capacitance equivalent thickness (CET) for ZrO 2 film with Al electrode was increased to about 12.4 Å compared with the film with Pt electrode due to the additional interfacial layer between Al and ZrO 2 film. The difference of flat band voltage (Δ V FB) between the films with two different electrodes was about 1.2 V because of their work function difference.

An Operational Large-Scale Marine Planetary Boundary Layer Model

A marine planetary boundary layer (PBL) model is presented and compared with data from sea-based experiments. The PBL model comprises two layers, the outer an Ekman-Taylor layer with stratification-dependent secondary flow, and the logarithmic surface layer corrected for stratification and humidity effects and variable surface roughness. Corrections are noted for air much warmer than water in stable conditions and for low wind speeds. The layers are analytically defined along with similarity relations and a resistance law for inclusion in a program. An additional interfacial layer correction is developed and shown to be significant for heat flux calculations. Experimental data from GOASEX were used to predict the windfield in the Gulf of Alaska, and JASIN data was used for windfields SE of Iceland. The JASIN-derived wind field predictions were accurate to within 1 m/sec and 10 deg in a 200 km triangle.