Oxide Window Research Articles

고효율 실리콘 박막태양전지를 위한 신규 수소저감형 비정질실리콘 산화막 버퍼층 개발

We propose a novel hydrogen-reduced p-type amorphous silicon oxide buffer layer between TiO₂ antireflection layer and p-type silicon window layer of silicon thin film solar cells. This new buffer layer can protect underlying the TiO₂ by suppressing hydrogen plasma, which could be made by excluding H2 gas introduction during plasma deposition. Amorphous silicon oxide thin film solar cells with employing the new buffer layer exhibited better conversion efficiency (8.10 %) compared with the standard cell (7.88 %) without the buffer layer. This new buffer layer can be processed in the same p-chamber with in-situ mode before depositing main p-type amorphous silicon oxide window layer. Comparing with state-of-the-art buffer layer of AZO/p-nc-SiOx:H, our new buffer layer can be processed with cost-effective, much simple process based on similar device performances.

Application of indium zinc oxide window layers in Cu(In,Ga)Se2 solar cells

Recently, indium-based transparent conductive oxides have become more interesting for application in Cu(In,Ga)Se2 (CIGS) solar cells. Although the fabrication costs may be higher than for standard ZnO:Al (AZO), amorphous indium zinc oxide (IZO) films are very attractive due to their high charge carrier mobilities leading to high conductivity. Additional advantages are that the substrate does not need to be heated during sputter coating and that the films demonstrate superior stability against humidity.We investigate the deposition of IZO films by RF and DC magnetron sputtering in dependence of sputtering power, total pressure, oxygen and hydrogen admixture, and substrate temperature. The IZO films on glass are analysed by means of conductivity, spectral transmittance, and Hall measurements as well as X-ray diffraction and scanning electron microscopy. Specific resistivity below 350μΩcm is obtained for 0.4μm thick films, half that of AZO. Best mobilities of about 50cm2/Vs are achieved for highly transparent films.The suitability of IZO as a window layer for CIGS solar cells is demonstrated with efficiencies as high as 19.5% comparable to the AZO reference. Results for stability tests of IZO-coated CIGS modules in damp heat will be discussed.

Improved Low-Temperature Activity of CuO–CeO2–ZrO2 Catalysts for Preferential Oxidation of CO in H2-Rich Streams

In this work, CuO–CeO2–ZrO2 catalysts for CO preferential oxidation have been prepared by ultrasound assisted reverse coprecipitation and slow coprecipitation, and characterized via BET, XRD, XPS and H2-TPR techniques, respectively. It is found that the catalyst prepared with ultrasound assisted reverse coprecipitation preserves large specific surface area, fine crystalline grain and high dispersion of active copper species. Meanwhile, the reducibility is improved significantly and more active copper species and oxygen vacancies are formed in the copper–ceria boundaries. The ultrasound assisted reverse coprecipitation prepared CuO–CeO2–ZrO2 catalyst exhibits superior low-temperature activity and CO2 selectivity, over which the temperature responding to 50 % CO conversion is as low as 67 °C, and the temperature window of full CO conversion is significantly widen from 100 to 160 °C. The ultrasound assisted reverse coprecipitation prepared CuO–CeO2–ZrO2 catalyst exhibits superior low-temperature activity for CO preferential oxidation and wide temperature window of full CO conversion comparing with the catalyst prepared with slow coprecipitation.

Enhanced electrochemical performance of LiNi0.5Mn1.5O4 cathode using an electrolyte with 3-(1,1,2,2-tetrafluoroethoxy)-1,1,2,2-tetrafluoropropane

A new electrolyte based on fluorinated 3-(1,1,2,2-tetrafluoroethoxy)-1,1,2,2-tetrafluoropropane (F-EPE) solvent is studied in LiNi0.5Mn1.5O4/Li cells. The electrochemical stability of the electrolyte with 10% F-EPE is carried out by linear sweep voltammetry and electrochemical floating test. These results indicate that the electrolyte with F-EPE has an oxidation potential of more than 5.2 V vs. Li+/Li, which is higher than that without F-EPE and enlarges the oxidative window of electrolyte. A thin and uniform SEI layer is formed on the surface of LiNi0.5Mn1.5O4 cathode by using electrolyte with F-EPE, leads to an improvement in the electrochemical performance, validated by charge-discharge tests, EIS, SEM, TEM, and XPS analysis.

Numerical Study of TCO/Silicon Solar Cells with Novel Back Surface Field

ZnS/Si/CuO heterostructure is investigated by a theoretical approach as a possible low-cost design for photovoltaic conversion in the track of the heterojunction with intrinsic thin layer solar cells. Our results indicate that, owing to perfect electron affinity and lattice matching properties, zinc sulfide with adequate Al doping can efficiently replace zinc oxide window layer as an emitter region for silicon-based solar cells. Lattice mismatch, energy band alignment at the interfaces and material resistivity are the framework parameters of the study. By focusing on the open circuit voltage parameter, the back metal/Si and silicon base doping were optimized so that the conversion efficiency was increased from 3.37% to 15.19%. The introduction of a cupric oxide (CuO) layer acting as a p + back surface field with a bandgap of 1.35 eV and appropriate doping as high as 7 × 1018 cm−3 can enhance the conversion efficiency to 17.30%, provided that the silicon material remains free from contamination by copper atoms and also by performing a suitable treatment of CuO to lower its resistivity.

Luminescence mechanism for Er3+ ions in a silicon-rich nitride host under electrical pumping

A combined experimental and theoretical study on the electroluminescent excitation mechanism for trivalent erbium (Er3+) ions in a silicon-rich nitride (SiNx) host is presented. Direct impact by hot electrons is demonstrated to be the fundamental excitation mechanism. The Er3+ excitation by energy transfer from silicon nanostructures and/or defects is shown to be marginal under electrical pumping. A bilayer structure made of a SiO2 electron-accelerating layer and an Er-implanted SiNx layer has been sandwiched between a metal–insulator–semiconductor structure with a highly doped N-type silicon substrate and an indium–tin–oxide window functioning as a transparent electrode. Monte Carlo (MC) simulations are used to model hot electron transport in the proposed device structure. Acoustic, polar and non-polar optical electron–phonon scattering mechanisms are considered as well as a new scattering process related to the trapping/detrapping on energetically shallow traps in the band gap of silicon nitride. For SiO2 layers around 20 nm-thick and beyond, the number and kinetic energy of hot electrons before entering the SiNx layer are maximal. A significant enhancement of the 1.54 μm electroluminescence power efficiency of two orders of magnitude is observed in devices composed of a 20 nm-thick SiO2 layer compared to those composed of 10 nm-thick SiO2. We demonstrate by MC simulations that such a difference, in terms of power efficiency, is ascribed to the high-energy tail of the hot electron energy distribution, which becomes more pronounced as the SiO2 electron-accelerating layer thickness increases. It is also unveiled that direct excitation of the 1.54 μm Er3+ main radiative transition requiring an excitation energy of only 0.8 eV is inefficient, and that the major part of the Er3+ ions are excited via higher level energy states. The obtained results are sufficiently consistent to be extended to other trivalent rare-earth ions inside similar insulating material environments.

Au nanoparticle enhanced thin-film silicon solar cells

Gold nanoparticles (Au NPs) were prepared on the top of the indium tin oxide (ITO) window layer in thin-film silicon solar cells using a magnetron sputtering method. In comparison with the pure ITO film, the samples with the Au NPs show higher optical transmittance. It is found that the photoluminescence (PL) intensities from the ITO films are enhanced significantly by the Au NPs, so do the macroscopic conductance and the microscopic conductive atomic microcopy (C-AFM) current–voltage (I–V) characteristics. It also appears that the surface work function (φs) is changed by the Au NPs, the longer time the Au NP deposition, the more Au NPs on surface, the larger φs. When the sample is illuminated, its φs downshifts due to the local surface plasmon resonance (LSPR) excited by the illumination on the Au NPs. It is found that the short circuit current density (Jsc) of the solar cells is increased by as much as 20.78% for the optimized solar cell configuration.

An investigation of functionalized electrolyte using succinonitrile additive for high voltage lithium-ion batteries

Succinonitrile (SN) has been used as functional additive to improve the thermal stability and broaden the oxidation electrochemical window of commercial electrolyte 1 M LiPF6/EC/DEC (1:1, by volume) for high-voltage LIBs (cathode: Li1.2Ni0.2Mn0.6O2, anode: Li). 1 wt % SN-based electrolyte showed a wide electrochemical oxidation window of 5.4 V vs Li+/Li and excellent thermal stability demonstrated by thermogravimetry (TG) and X-ray photoelectron spectroscopy (XPS), as well as theoretical analysis according to molecular orbital theory. The LNMO (Li1.2Ni0.2Mn0.6O2) battery with 1 wt % SN-based electrolyte showed better cyclability and capacity retention when charged to higher cut-off voltage. The improved battery performance is mainly attributed to the formation of uniform cathode electrolyte interface (CEI) formed by interfacial reactions between the LNMO cathode and electrolyte. The outcome of this work and the continuous research on this subject can generate critical knowledge for designing thermal stability electrolytes for large format lithium-ion batteries.

Restricted-Access Al-Mediated Material Transport in Al Contacting of PureGaB Ge-on-Si p + n Diodes

The effectiveness of using nanometer-thin boron (PureB) layers as interdiffusion barrier to aluminum (Al) is studied for a contacting scheme specifically developed for fabricating germanium-on-silicon (Ge-on-Si) p + n photodiodes with an oxide-covered light entrance window. Contacting is achieved at the perimeter of the Ge-island anode directly to an Al interconnect metallization. The Ge is grown in oxide windows to the Si wafer and covered by a B and gallium (Ga) layer stack (PureGaB) composed of about a nanometer of Ga for forming the p + Ge region and 10 nm of B as an interdiffusion barrier to the Al. To form contact windows, the side-wall oxide is etched away, exposing a small tip of the Ge perimeter to Al that from this point travels about 5 μm into the bulk Ge crystal. In this process, Ge and Si materials are displaced, forming Ge-filled V-grooves at the Si surface. The Al coalesces in grains. This process is studied here by high-resolution cross-sectional transmission electron microscopy and energy dispersive x-ray spectroscopy that confirm the purities of the Ge and Al grains. Diodes are fabricated with different geometries and statistical current–voltage characterization reveals a spread that can be related to across-the-wafer variations in the contact processing. The I–V behavior is characterized by low dark current, low contact resistance, and breakdown voltages that are suitable for operation in avalanching modes. The restricted access to the Ge of the Al inducing the Ge and Si material transport does not destroy the very good electrical characteristics typical of PureGaB Ge-on-Si diodes.

Epitaxial diamond-hexagonal silicon nano-ribbon growth on (001) silicon.

Silicon crystallizes in the diamond-cubic phase and shows only a weak emission at 1.1 eV. Diamond-hexagonal silicon however has an indirect bandgap at 1.5 eV and has therefore potential for application in opto-electronic devices. Here we discuss a method based on advanced silicon device processing to form diamond-hexagonal silicon nano-ribbons. With an appropriate temperature anneal applied to densify the oxide fillings between silicon fins, the lateral outward stress exerted on fins sandwiched between wide and narrow oxide windows can result in a phase transition from diamond-cubic to diamond-hexagonal Si at the base of these fins. The diamond-hexagonal slabs are generally 5–8 nm thick and can extend over the full width and length of the fins, i.e. have a nano-ribbon shape along the fins. Although hexagonal silicon is a metastable phase, once formed it is found being stable during subsequent high temperature treatments even during process steps up to 1050 ºC.

Hydrogenated indium oxide window layers for high-efficiency Cu(In,Ga)Se2 solar cells

High mobility hydrogenated indium oxide is investigated as a transparent contact for thin film Cu(In,Ga)Se2 (CIGS) solar cells. Hydrogen doping of In2O3 thin films is achieved by injection of H2O water vapor or H2 gas during the sputter process. As-deposited amorphous In2O3:H films exhibit a high electron mobility of ∼50 cm2/Vs at room temperature. A bulk hydrogen concentration of ∼4 at. % was measured for both optimized H2O and H2-processed films, although the H2O-derived film exhibits a doping gradient as detected by elastic recoil detection analysis. Amorphous IOH films are implemented as front contacts in CIGS based solar cells, and their performance is compared with the reference ZnO:Al electrodes. The most significant feature of IOH containing devices is an enhanced open circuit voltage (VOC) of ∼20 mV regardless of the doping approach, whereas the short circuit current and fill factor remain the same for the H2O case or slightly decrease for H2. The overall power conversion efficiency is improved from 15.7% to 16.2% by substituting ZnO:Al with IOH (H2O) as front contacts. Finally, stability tests of non-encapsulated solar cells in dry air at 80 °C and constant illumination for 500 h demonstrate a higher stability for IOH-containing devices.

Radio frequency plasma deposited boron doped high conductivity p-type nano crystalline silicon oxide thin film for solar cell window layer

Wide band gap p-type nano crystalline silicon oxide (p-nc-SiO:H) window layer is useful for multi junction solar cells. We prepared such a material by using high hydrogen dilution and low plasma power that shows high optical gap as well as high conductivity. By varying CO2 flow rates of from 0.3 to 2.5 sccm we obtained the films with crystallite volume fraction (Xc) ranging from 43.7% to 4.5%, while by decreasing the plasma power density from 426, to 28 mW/cm2 the Xc was observed to increase from 14.0% to 45.8%. At a high plasma power the hydrogen dilution did not show significant change in film properties. The electrical conductivity and activation energy was observed to be favorable at low plasma power density, which was 3.4 × 10−2 S cm−1 and 0.102 eV respectively at 28 mW/cm2 plasma power density. It is expected that at a low plasma power a large number of SiH3 radicals actively take part in film deposition, leading to an improved film properties. Solar cells fabricated with the selected p-nc-SiO:H, shows improved short wavelength response of the quantum efficiency, indicating the advantage of using such p-type materials. The optical gap of these p-nc-SiO:H films were in the range of 1.784 to 2.130 eV.

A new technique in LDMOS transistors to improve the breakdown voltage and the lattice temperature

A new technique for high breakdown voltage of the LDMOS device is proposed in this paper. The main idea in the proposed technique is to insert the P+ silicon windows in the buried oxide at the interface of the n-drift to improve the breakdown voltage, electric field and maximum lattice temperature. The proposed structure is called as P+ window LDMOS (PW-LDMOS). It is shown by extending the depletion region between the P+ windows and the n-drift region, the breakdown voltage of PW-LDMOS increases to 405V from 84V of the conventional LDMOS on 1µm silicon layer and 2µm buried oxide layer. Also, effective values of doping, length, and depth of P+ window are investigated in the breakdown voltage. Moreover, a self-heating-effect is alleviated by the silicon windows in comparison with the conventional LDMOS. All the achieved results have been extracted by two-dimensional and two-carriers simulator ATLAS.

3-(1,1,2,2-Tetrafluoroethoxy)-1,1,2,2-tetrafluoropropane as a High Voltage Solvent for LiNi1/3Co1/3Mn1/3O2/Graphite Cells

A new electrolyte based on fluorinated 3-(1,1,2,2-tetrafluoroethoxy)-1,1,2,2-tetrafluoropropane (F-EPE) solvent is developed to decrease the capacity fading of LiNi1/3Co1/3Mn1/3O2/graphite lithium-ion batteries (LIBs) cycled in the voltage range of 3.0–4.5 V (vs. Li/Li+). The linear sweep voltammetry (LSV) and cyclic voltammetry (CV) indicate that F-EPE has an oxidation potential of more than 5.4 V vs. Li/Li+, which is higher than traditional solvents and enlarges the oxidative window of electrolyte. Especially, compared with the LiNi1/3Co1/3Mn1/3O2/graphite cells without F-EPE in the electrolyte, the capacity retentions of the cells contained 20 wt% F-EPE and cycled in 3.0–4.5 V are significantly increased from 12.3% to 85.0% after 100 cycles. In addition, the cathode and the anode are respectively characterized in three-electrode systems by electrochemical impedance spectrum (EIS), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and transmission electron microscopy (TEM) to elaborate the reaction mechanism of F-EPE in the cells. The enhanced performances can be ascribed to that F-EPE cannot only greatly improve the oxidation stability of electrolyte solutions but also participate in the formation of passivation film on the graphite anode, indicating the positive effect of F-EPE on the performances of LIBs cycled in 3.0–4.5 V.

Fabrication of a Complete Photovoltaic CIGS Device by Electrodeposition

Copper Indium Gallium Selenium (CIGS) films are attractive for photovoltaic applications due to their high optical absorption coefficient. Generation of CIGS films by electrodeposition is particularly appealing due to the relatively low capital cost and the relatively high throughput1-3. Numerous publications address the electrodeposition of CIGS; however, to our knowledge, none reports the fabrication of a complete CIGS photovoltaic cell using electrochemical techniques.In this work we introduce electrochemical processes that enable the fabrication of complete CIGS and CIGSS functional photovoltaic devices, based entirely on electroplating. The electrodeposition of the CIGS or CIGSS absorber layers is based on an electrolyte that is far more dilute than systems that had been traditionally used, and which yields much improved CIGS and CIGSS films4,5. In addition to the absorber layer, electrochemical processes for the electrodeposition of the cadmium sulfide (50 nm), and the pure zinc oxide (100 nm) layer are described. Also the electrodeposition of doped zinc oxide (0.5 µ) (window layer) is discussed. The substrate has been stainless steel coated with electrodeposited metal barrier (Ni, Cr, or Cu), enabling continuous strip plating. An intermediate molybdenum layer, providing improved interface to the absorber layer, increased the efficiency. The final device structure is shown in figure 1.Complete electrodeposited devices were generated and tested exhibiting efficiencies ranging from 2 to 6% with quantum efficiency exceeding 0.6 as shown in figure 2. A comprehensive electrochemical process such as described here, will enable the fabrication of the entire device through a fast wet chemical process, providing effective manufacturing integration and scaling.

Quantitative measurements of HO2/H2O2 and intermediate species in low and intermediate temperature oxidation of dimethyl ether

As two of the most important species that characterize hydrocarbon low temperature ignition, HO2 and H2O2 formation during dimethyl ether (DME) oxidation was quantified using the same experimental conditions, for the first time, in an atmospheric flow reactor at low and intermediate temperature range. Dual-Modulation Faraday Rotation Spectroscopy (DM-FRS) and Molecular Beam Mass Spectrometry (MBMS) were used to measure HO2 and H2O2 respectively. DME and other important intermediate species such as CH2O and CO are also measured by MBMS between 400 and 1150K at different fuel concentrations. Species profiles in the reactor were calculated by using both zero- and two-dimensional computations with different detailed kinetics for cross-validation and comparison with experimental results. The models predict adequately the low and intermediate oxidation temperature windows near 600 and 1000K, respectively. However, both models over-predicted the DME consumption as well as CO, HO2 and H2O2 formations at the low temperature oxidation window by more than a factor of four. Moreover, although the model predicted reasonably well the formation of CH2O and CO/CO2 at the intermediate temperature oxidation window, the concentration of H2O2 was also over-predicted, suggesting the large uncertainties existing in the DME low temperature chemistry and in H2O2 chemistry at intermediate temperature. Furthermore, to analyze the uncertainty of the low temperature chemistry, a branching ratio of QOOH decomposition to CH2O was derived using measured DME, CH2O and CO concentrations. The large difference between the modeled and measured branching ratios of QOOH decomposition suggests an underestimated QOOH decomposition rate to form CH2O in the current DME models.

A numerical modeling on the emission characteristics of a diesel engine fueled by diesel and biodiesel blend fuels

A numerical modeling study was performed to investigate the impacts of biodiesel blend ratio on the emission formation processes of a diesel engine. Simulations were conducted using 3-D CFD simulation software KIVA4 coupled with CHEMKIN II. The integrated chemical kinetics with 69 species and 204 reactions comprises the significant reaction pathways of methyl decanoate (C11H22O2), methyl-9-decenoate (C11H20O2) and n-heptane (C7H16), which are capable of emulating different biodiesel blend ratios. The nitrogen monoxide (NO) and carbon monoxide (CO) formation mechanisms were also embedded. To better represent the biodiesel fuel properties, detailed chemical and thermo-physical properties of biodiesel were calculated and integrated into the KIVA4 fuel library. The simulated cases were validated against the experimental results by comparing the in-cylinder pressure and heat release curves for B100, B50, and pure diesel fuels at 2400rpm under 10% load, 50% load and 100% load, respectively. Good agreements with a maximum of 5% deviation on the peak cylinder pressure were obtained. Simulation results revealed that at 10% load conditions, with the increase of biodiesel blend ratio, the overall CO development and oxidation window is narrowed, and a remarkable increase in CO emission is observed.

Transition metal oxide window layer in thin film amorphous silicon solar cells

Pin-type hydrogenated amorphous silicon solar cells have been fabricated by replacing state of the art silicon based window layer with more transparent transition metal oxide (TMO) materials. Three kinds of TMOs: vanadium oxide, tungsten oxide, and molybdenum oxide (MoOx) were comparatively investigated to reveal the design principles of metal oxide window layers. It was found that MoOx exhibited the best performance due to its higher work function property compared to other materials. In addition, the band alignment between MoOx and amorphous Si controls the series resistance, which was verified through compositional variation of MoOx thin films. The design principles of TMO window layer in amorphous Si solar cells are summarized as follows: A wide optical bandgap larger than 3.0eV, a high work function larger than 5.2eV, and a band alignment condition rendering efficient hole collection from amorphous Si absorber layer.

Amorphous silicon oxide window layers for high-efficiency silicon heterojunction solar cells

In amorphous/crystalline silicon heterojunction solar cells, optical losses can be mitigated by replacing the amorphous silicon films by wider bandgap amorphous silicon oxide layers. In this article, we use stacks of intrinsic amorphous silicon and amorphous silicon oxide as front intrinsic buffer layers and show that this increases the short-circuit current density by up to 0.43 mA/cm2 due to less reflection and a higher transparency at short wavelengths. Additionally, high open-circuit voltages can be maintained, thanks to good interface passivation. However, we find that the gain in current is more than offset by losses in fill factor. Aided by device simulations, we link these losses to impeded carrier collection fundamentally caused by the increased valence band offset at the amorphous/crystalline interface. Despite this, carrier extraction can be improved by raising the temperature; we find that cells with amorphous silicon oxide window layers show an even lower temperature coefficient than reference heterojunction solar cells (−0.1%/°C relative drop in efficiency, compared to −0.3%/°C). Hence, even though cells with oxide layers do not outperform cells with the standard design at room temperature, at higher temperatures—which are closer to the real working conditions encountered in the field—they show superior performance in both experiment and simulation.

Thickness Optimization of Various Layers of CZTS Solar Cell

Thin film solar cells based on Cu2ZnSnS4 (CZTS) absorbers are proposed with the structure glass/Mo/CZTS/buffer/ZnO. In this work we have simulated CZTS thin film solar cell using solar cell capacitance simulator (SCAPS). The influences of thickness of (CZTS) absorber, thickness of (CdS) buffer layer and Zinc oxide window Layer (ZnO) on the photovoltaic cell parameters are studied. It can be seen after reviewing the results, that for high conversion efficiency, the cell should have a thin (...)