bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of an Unidentified Phonon Peak in SiGe Alloys and Superlattices Using Molecular Dynamics Simulation
Authors: Chung Sylvia Yuk Yee , Tomita Motohiro , Yokogawa Ryo , Ogura Atsushi , Watanabe Takanobu
Published: December 2020

Advancements in semiconductor technology coincide with an increasing need for better understanding of thermal transport and phonon behaviour in such devices. The difficulty lies with observing and measuring these phonon properties, oftentimes proving to be a challenge due to the limitations posed by instrumental capabilities. Yokogawa et al [1] obtained inelastic X-ray scattering results for SiGe alloys, and found an unidentified phonon mode (~ 50 – 150 cm-1) within the phonon spectra. Determining the possible conditions for producing this unknown mode drove the motivation for this current study and thus, forms the theme for this project.

A variety of SiGe structures consisting of alloys, a compound and superlattices, were simulated using molecular dynamics to obtain the phonon dispersion relations in order to observe the unknown mode. All of the SiGe alloys produced the unknown mode, but the SiGe compound did not. The alloys are configured with a random atomic configuration, but the SiGe compound is given an Si-Ge-Si-Ge atomic configuration, indicating that the unknown mode has a tendency to only show for structures of an alloy nature. Regarding the superlattices, structures consisting of periodic layer widths did not produce the unknown mode, whereas aperiodic structures did. This tendency increased as the layer widths reduced.

The origin of this unknown mode is still yet to be determined, but what we can conclude so far, is that this mode will only appear when the structure adopts a random atomic configuration, with a preference leaning away from periodicity.

Acknowledgements

This work was supported by a CREST grant (JPMJCR19Q5) from the Japan Science and Technology Agency (JST).

References

[1] R. Yokogawa, Oyanagi, H. Uchiyama, S.Tsutsui, I. Yonenaga, A. Ogura, Phonon Dispersion Measurements for Bulk Si1-xGex (x=0.72) Crystal by Inelastic X-ray Scattering, The 80th JSAP Autumn Meeting, Hokkaido Univ. Japan, 19/09/2019

Figure 1
Development of Bifunctional Electrocatalyst By Palladium Deposition on Modified Perovskite La0.6Sr0.4Co0.2Fe0.8O3-Δ for Li−O2 Battery
Authors: Oh Mi Young , Kang Seok Jun , Son Hyeon no , Shin Tae Ho
Published: December 2020

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) perovskites have previously emerged as efficient cathode catalysts for various electrochemical devices such as lithium-air cathode, since its superior chemical stability and mixed electron-ion conductivity. LSCF exhibits good activity for the oxygen evolution reaction (OER) as cathode catalysts. However, the activity on Oxygen Reduction Reaction (ORR) is still a barrier to be utilized as a catalyst for low-temperature electrochemical devices such as lithium-air battery. Bifunctional electrocatalyst is important to reduce the large overpotential involved the sluggish kinetics of the ORR and OER at the air electrode in lithium-air battery. In this work, palladium (Pd) contents were deposited on the nano-sized LSCF surface to improve its ORR activity in lithium-air battery. When the 20 wt.% Pd/Nano-LSCF were applied to cathode catalyst in Li-O2 battery, higher initial discharge capacity (16912 mAh g-1) compared with Nano-LSCF (6707 mAh g-1) was obtained. These results demonstrate the deposition of Pd can be an effective catalyst to enhance the ORR activity of perovskite LSCF.
The Effect of Electrolyte Additive on the Performance of Cathode Based on Anion Redox
Authors: KIM Hyung Gi , Park Yong Joon
Published: December 2020

As the expansion of application fields for lithium ion batteries (LIBs) from cell phones to electric vehicles, AI robots, drones and wearable devices, enhanced LIBs with high capacity and enhanced energy efficiency have been needed. Until now, most of LIBs has been used transition metal oxides as cathodes, which deliver their capacity based on cationic redox reaction. However, their capacity has almost reached the limit. Recently, several oxides based on anionic redox reaction have been suggested as new cathode with higher capacity compared to commercial cathodes based on cationic redox reaction. Among them, lithia based cathodes has attracted a lot of attention due to their high theoretical capacity and stable cyclic performance. Lthia based cathode is composed of lithia presenting the capacity based on anionc redox and catalyst activating the lithia. Moreover, to compensate for the low conductivity of lithia, carbon should be composited with them. The lithia based cathode have larger capacity than the commercial cathodes, however, they are vulnerable with electrolyte due to the reactive lithia. In this study, the electrolyte additives are introduced to suppress the undesirable side reaction between lithia based cathode and electrolyte. Furthermore, new approach for mixing with carbon is tried for enhancing the efficiency of the lithia based cathode. The effect of electrolyte additive and carbon mixing method are characterized using electrochemical test and XPS analysis in this work.
Solution-Phase Synthesis and Electrochemical Properties of Lepidocrocite Titanate-Reduced Graphene Oxide Composites
Authors: Barim Gözde , Lin Jason , Doeff Marca M
Published: December 2020

Stepped layered titanates can be used as anodes for lithium, sodium or potassium batteries in conventional or flow cell configurations. They are attractive due to their low cost, low toxicity, and high abundancy. However, their low conductivity and poor cycling performance are major hurdles for these materials.The addition of carbon can be used to overcome electronic transport limitations to some extent, but for nonconventional configurations, it is preferable to build in the conductivity by manipulating the structure. For example, in the case of layered materials, this can be done by incorporating a conductive component such as reduced graphene oxide (rGO) in the van der Waals gaps to make 2D heterostructures, the approach we are using here.

In this presentation, solution-phase synthesis of K0.8[Ti1.73Li0.27]O4 (lepidocrocite titanate, LT)- rGO composite is demonstrated. After synthesis by conventional solid-state routes, K0.8[Ti1.73Li0.27]O4 is proton exchanged and ion-exchanged with bulky cations, causing expansion of the structure, and exfoliated by mechanical shaking. Exfoliated layered titania sheets are combined with reduced graphene oxide (rGO) to assemble into heterostructures through flocculation. Counter cations (e.g. Mg2+, Na+) are used for the self-assembly of negatively charged LT and rGO nanosheets via flocculation. Mg2+-coagulated composites with 15 wt% rGO have higher capacities than Na+-coagulated composites with the same rGO content in the lithium half-cell configurations, whereas Na+-coagulated composites deliver higher capacity than that of Mg2+-coagulated composites in the sodium half-cell configurations. Both Mg2+-coagulated and Na+-coagulated LT-rGO samples exhibit capacities which are more than two times higher than the capacities of pristine lepidocrocite titanate (K0.8[Ti1.73Li0.27]O4), and display good capacity retention after 50 cycles in both lithium and sodium half-cells configurations.
Enhanced Cathode Reactions of the Solid-State Li-Air Battery By Operating Under Humidified Atmosphere
Authors: Kim Mokwon , Ma Sang Bok , Kwon Hyuk Jae , Lee Hyunpyo , Park Jung Ock , Im Dongmin
Published: December 2020

Lithium-air (Li-air) battery has been considered to be a promising next-generation energy storage system owing to its high theoretical specific energy of 3,458 Wh/kg. Despite the progresses that have been made to improve the cell performance and reaction kinetics of Li-air battery, achieving its sustained reversibility still remains as a highly challenging goal because of the use of liquid electrolyte and carbonaceous materials in the cathode. These components could easily decompose by side reactions against highly oxidative radicals during cycling, leading to a poor cycle life of the cell. To address this instability issue, stable all-solid-state cathode has attracted research attention in accordance with the recent development of oxide-based solid electrolytes. Although a few meaningful approaches to demonstrate oxide-based solid-state cathodes have been reported, such cells were operated under pure oxygen atmosphere (Li-O2 battery), resulting in limited active interfaces for oxygen redox reactions and low specific capacity to the total weight of the cathode structure.

Herein, we report the enhanced cathode reactions for Li-air battery by operating under humidified oxygen atmosphere to overcome the limitation of conventional oxide-based solid-state Li-O2 battery. For the cathode, a novel solid-state composite cathode structure consists of ruthenium-based oxide nanoparticles without any carbonaceous additives was prepared to catalyze the oxygen redox reactions. During cycling, the vaporized water molecules could significantly increase the discharge potential, discharge rates, and round-trip efficiency of the cathode. The morphological and structural analysis of the discharge products formed via water-involved reactions inside the pore structure, not only at the interfaces, were also conducted to figure out the effects of humidification. The resulting solid-state Li-air battery showed a superior cycle life with the high specific capacity to the cathode compared to conventional solid-state Li-O2 batteries. The details of the cathode properties and cell performances will be discussed in the presentation.
Parasitic Reactions Due to Singlet Oxygen and Possible Approaches in Lithium-Oxygen Batteries
Authors: Kwak Won-Jin
Published: December 2020

Irreversible parasitic reactions cause poor rechargeability and efficiency of Li-O2 batteries, and have predominantly been ascribed to the reaction of reduced oxygen species with cell components.

Recently, it was demonstrated that singlet oxygen (1O2) formed at the cathode during discharge and from the onset of charge accounts for the majority of parasitic reaction rather than reduced oxygen species.

In this presentation, I summarize the current knowledge about parasitic reactions of singlet oxygen in lithium-oxygen batteries and guide pathways to counteract this problem for reversible system.
Stabilized 3-D Foam for Ultra-Stable and Fast-Charging Lithium Metal Anode
Authors: Kim Do-Kyung , Ponraj Rubha , Yun Jong Hyuk
Published: December 2020

Current lithium ion batteries almost reached the practical energy density and needs further innovation at materials chemistry and design. Lithium metal holds the highest specific capacity among the possible anode materials for Li-ion batteries. However, the complex and parasitic interfacial reaction between lithium metal and electrolyte hinders the practical application of lithium metal as anode in secondary batteries. Therefore, stabilizing the interface of lithium metal is crucial for their application in automotive batteries and grid-scale energy storage devices. In this study, the interface of the lithium metal anode was tailored using a simple and strategical approach by a) regulating uniform deposition and stripping of lithium ions on to the 3-D structured foam and b) stabilizing the cycle life of the anode. A facile and cost effective method was adopted to uniformly deposit the carbon material on to the 3-D scaffold. The performance was analyzed using various structural and electrochemical performance studies. As a result of this study, the Li-ion cell delivered a stable cycling performance of over 400 cycles with 98.5% Coulombic efficiency. Also, post-mortem analysis of the lithium metal anode was performed to establish fundamental understanding on the interfacial protection mechanism. These results provide valuable insights for advanced design of lithium metal anode with uniform protective coating.
(Invited) Ultrahigh Areal Capacity Holey Graphene Air Cathodes for Li-O2 and Li-CO2 Batteries
Authors: Lin Yi , Connell John W.
Published: December 2020

Advanced lithium (Li) batteries using gaseous cathode reactants such as oxygen (O2) and carbon dioxide (CO2) are attractive energy storage platforms because the gases are obtained externally and thus not accounted for in the total battery weight when fully charged. The discharge products at the cathode, typically Li2O2 for Li-O2 batteries and Li2CO3for Li-CO2 batteries, are insoluble in the electrolyte. Therefore, in order for such batteries to function properly, an “air cathode”, which is a conductive scaffold within the battery cell, is required as a physical location for cathode electrochemical reactions to occur. Prior research has identified many carbon nanomaterials such as carbon nanotubes and graphene as viable choices for air cathode scaffold, while various metallic and metal-free catalytic systems integrated onto carbon-based air cathodes have been developed to improve the sluggish discharge and charge reactions. For future practical applications, the air cathode must exhibit a usable capacity per unit electrode area, or areal capacity, a critical parameter that has been largely overlooked so far in this field. In order to achieve high areal capacity, the air cathode must exhibit a sufficient amount of accessible void volume per unit electrode area while maintaining the conductive scaffold integrity during the entire electrochemical process.

Here we present an ultrathick, holey graphene-based air cathode platform fabricated from a facile dry compression process that exhibits remarkable areal capacity values. Holey graphene is a carbon nanomaterial derived from graphene, but with nanometer sized holes through the nanosheet thickness. The holes are generated in a controlled air oxidation process in which the defective carbon on the graphene surface are selectively oxidized and removed. The presence of these holes enhances mass transport through electrode thickness and also enables the unique dry-press fabrication process that is not achievable using other carbon scaffold materials. The dry-pressed holey graphene air cathode platform is compatible with catalyst incorporation to improve battery reaction kinetics. This platform also allows for novel engineering of electrode architectures not achievable using conventional electrode fabrication approaches. The applications of such highly versatile, ultrahigh areal capacity air cathode platforms to both Li-O2 and Li-CO2 battery chemistries will be discussed.
Stress Evolution in Lithium Metal Electrodes and the Impact of Artificial Passivating Layers
Authors: Cho Jung Hwi , Xiao Xingcheng , Guo Kai , Gao Huajian , Sheldon Brian W.
Published: December 2020

The potential advantages of lithium (Li) metal anodes have been widely touted (lowest reduction potential, etc.). However, the poor stability of Li metal / liquid electrolyte interfaces leads to chronic problems, such as dendrite formation and capacity loss. The possible impact of mechanical effects on interface stability and dendrite formation is a critical question that is difficult to probe directly. In-situ curvature measurements are an important tool for monitoring stresses during battery cycling. Using this technique during Li plating and examining film thickness effects, it is possible to separate contributions from the bulk lithium metal and the solid electrolyte interphase (SEI). These investigations show that significant stresses are created in the SEI films. Similar stress evolution measurements were also performed during lithium plating and stripping using both soft (PEO) and hard (LiF) artificial surface layers. The results indicate that stresses in surface films can be tuned to improve performance when artificial SEI layers are employed. A basic chemo-mechanical model indicates that hybridizing the two layers may benefit interface stability and performance in Li metal anodes.
Welcome Remarks - G03: SiGe, Ge, and Related Compounds: Materials, Processing, and Devices 9
Authors: Liu Qizhi
Published: December 2020

Welcome to G03: SiGe, Ge, and Related Compounds: Materials, Processing, and Devices 9! Take a moment to listen to welcome remarks from the lead organizer, Qizhi Liu.
Implementing Low Temperature Strategies to Advance “Really Cool” Molten Sodium Batteries
Authors: Spoerke Erik D. , Gross Martha , Percival Stephen , Peretti Amanda , Lamb Joshua , Small Leo J.
Published: December 2020

Though batteries for portable electronics and electric vehicles continue to advance at an impressive rate, the needs for safe, low-cost, reliable batteries suitable for large-scale implementation remain unsatisfied. Here, we describe advances toward a promising new class of low temperature molten sodium-halide batteries, capable of safe, reliable operation near 100oC, a dramatic reduction from the ~300oC operating temperatures common to traditional molten sodium batteries. While realizing this low temperature goal promises reduced system costs and improved material lifetimes, it introduces a host of new material performance challenges including molten catholyte phase control and electrochemistry, solid state separator performance, and charge transfer at critical solid-liquid interfaces. The new battery design described here relies on highly conductive NaSICON-based ion-conducting membranes to separate a molten sodium anode and, critically, a molten inorganic sodium iodide (NaI)-based halide salt catholyte. Through engineering of novel molten salt catholyte compositions, we have identified several chemistries capable of producing a high voltage (>3V) while avoiding problems of thermal runaway and electrolyte flammability. Our studies further show that catholyte composition not only impacts low temperature electrochemical performance, but also the accessible capacity and even techno-economic viability of the system. Implementing these catholytes in lab-scale prototypes with charge-transfer interfaces engineered for low-temperature operation, we have demonstrated 5 months of stable electrochemical cycling at 110oC. Continued refinement of these material-enabled strategies promises a new class of grid-scale energy storage technologies based on molten sodium.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
High TEC Copper to Connect Cu-Cu Pads for Wafer Bonding
Authors: Tran Anh , Hirato Tetsuji , Kondo Kazuo
Published: December 2020

Introduction

Cu/SiO2 hybrid bonding is a promising method for 3D stacking of integrated circuits in which the copper bonding of the interconnection pads and direct bonding of the silicon dioxide surface occur simultaneously.1 This bonding technology requires a damascene-like process on each sample to be bonded (wafers and/or chips), including copper deposition and chemical mechanical polishing (CMP), in order to create the copper bonding pads and lines.2 Due to the higher erosion rate of copper in comparison with silicon dioxide, a dishing effect on the surface of copper is generated. This effect can prevent bonding and thereby lead to electrical connection failure between top and bottom pads. In order to overcome this dishing effect and enhance the copper bonding at lower temperature, we developed a high thermal expansion coefficient (TEC) electrodeposited copper.

Result and discussion

Figure 1 shows the thermal expansions of conventional copper (black line) and electrodeposited copper with the high TEC additives (red curve). For the conventional copper, the expansion length at 300oC is 69 μm. Meanwhile, the expansion length of high TEC copper at 300oC is 90 μm, 30% higher than conventional copper.

Figure 2 shows the variation of contact area with annealing temperature for 4 nm dishing depth of circular copper pad for conventional copper and high TEC copper. Contact area values are calculated by the model in numerical study of C. Sart et al.3. Copper pad width is 4 μm and thickness is 500 nm. It can be easily seen that the contact area with high TEC copper is significantly higher than conventional copper. At 200oC, the contact area of conventional copper is only 63.5 %. Meanwhile, the contact area of high TEC copper is 93.6 %. Furthermore, 100% contact area is possible from 250oC for circular copper pads with dishing depth 4 nm.

Reference

Rebhan et al., 17th Electronics Packaging and Technology Conference Proceedings, 1-4 (2015).

Beilliard et al., International Journal of Solids and Structures (2016). DOI: 10.1016/j.ijsolstr.2016.02.041

Sart et al., 6th Electronic System-Integration Technology Conference (ESTC) (2016). DOI: 10.1109/ESTC.2016.7764484

Figure 1
Intelligent MOL(Middle-Of-Line) Design Methodology for 3D FinFET Manufacturability
Authors: MIN Jeong Guk , Noh Sang Do , Choi Jaehyuk
Published: December 2020

This research is an outstanding first study on the intelligent design methodology of the core MOL scheme. It can maximize the manufacturability of 3D FinFET technology that is mainly used for foundry AP products ranging from 10nm to 5nm.

In order to realize various MOL structures, 3D virtual process simulation considering plasma and surface reaction was implemented, and based on this, the generation of gate to contact short, a chronic defect in FinFET MOL scheme, could be detected without decap. Futhermore, for the feature selection, the process factor sensitivity analysis was performed with the Monte carlo algorithm, which is one of the representative reinforcement learning techniques, and it was found that the key factors of defect were gate to contact misalign and contact etch angle. In the Gate-to-Contact 3D minimum distance probability distribution function generated by millions of samplings based on this intelligent algorithm, the failure criteria can be obtained by mapping with the number of fail bits detected in the wafer.

As the device's scaling limit was reached, SCE-driven FEOL(Front-End-Of-Line) characteristics as well as the MOL parasitics' portion became very huge in the 10 nm or less FinFET technology, but all studies have been limited to the effects of device performance via RC(Resistance-Capacitance) analysis.

On the other hand, our methodology provides a 3D minimum distance 5.7nm specification for a defect-free MOL structure for the first time, and provides conditions to meet Gate to CNT short zero at the current process capability level when improving M/A 4.5nm and etch ang 1.5o. In silicon, the same result was obtained as predicted.

Figure 1
(Edward Goodrich Acheson Award Address) From Medical Applications to the Environment: The Important Role of Electrochemical Energy Storage
Authors: Takeuchi Esther S.
Published: December 2020

There is critical need for advances in electrochemical energy storage as the technologies are often pivotal for the success of an application. For example, transportation, personal electronics and biomedical applications have ever increasing demands for portable power. Further, stationary energy storage may be a key factor in the ability to broadly integrate intermittent renewable energy sources such as wind and solar. Despite remarkable advances in electrochemically active materials over the last several decades, there remains an urgent need to enhance utilization efficiencies and to develop materials that can safely deliver both high power and energy density.

An existing challenge for each specific system of electric energy storage is understanding the basic science associated with the gap between the usable output of the energy storage system and its theoretical energy content. The goal of overcoming this inefficiency is to achieve more useful work (w) and minimize the generation of waste heat (q). Optimization can be approached at the macro level, where bulk parameters are identified and manipulated. However, such a strategy may not provide insight toward the complexities of electric energy storage, especially the inherent heterogeneity of ion and electron flux contributing to the local resistances at numerous interfaces found over several scale lengths within a battery.

We are pursuing the investigation of factors that affect ion and electron transport including properties of electroactive materials, interfaces, and electrode structures. Recent advances in the use of in-situ and operando characterization techniques with spatio-temporal resolution of electrochemical activity have enabled us to gain significant mechanistic insight. The ability to understand and ultimately tune these complex electrochemical systems to specific applications, both current and future, depends on specific experimentation and understanding over multiple length scales.
(Invited) Defect and Impurity Characterization in Wide Bandgap Materials and Interfaces: Impact on Thermal Transport
Authors: Goorsky Mark S. , Hopkins Patrick E , Luo Tengfei , Henry Asegun , Graham Samuel , Doolittle W. Alan , Khan Asif , Liao Michael Evan , Bai Tingyu , Wang Yekan , Huynh Kenny
Published: December 2020

Wide bandgap materials are suitable for high power and high temperature applications. However, these materials, and metal layers that are part of device structures must effectively transport heat from the active device regions. Structural defects, chemical defects, and interface properties can degrade thermal transport, but relatively little attention has been paid to the precise nature of these defects and how they impact thermal transport. Electron microscopy and x-ray scattering based techniques are employed to provide insight into the defects present in these materials. When these techniques are integrated with thermal transport measurements and theoretical insights gained from molecular dynamics simulations, a much better understanding of thermal transport in wide bandgap materials can be realized. Examples of how defects impact transport for diamond boundary interfaces, AlN layers, and GaN heterostructures will be presented.
(Invited) 200mm GaN Power: Technology and Commercialization Status on Scalable QST® Platform
Authors: Odnoblyudov Vladimir , Aktas Ozgur , Basceri Cem
Published: December 2020

In recent years, GaN has become a forefront wide bandgap semiconductor material for next-generation, energy-efficient power electronics. With its higher breakdown strength, faster switching speed and lower on-resistance, GaN power devices can convert power far more efficiently than Si-based devices. While its performance is commercially demonstrated, widespread GaN adoption requires a scalable and high-yielding manufacturable technology platform enabling economies of scale and a full spectrum of low-cost products such as lateral and vertical power switches extending from 100V to 1,200V and beyond, monolithic ICs and rectifiers.

QROMIS’ disruptive commercial solution to high volume, low cost and scalable GaN device manufacturing has been steadily gaining traction, owing to unique properties of specially-designed CMOS fab-friendly and semi-spec substrate called “QST®” (QROMIS Substrate Technology) with a core having a thermal expansion that very closely matches the thermal expansion of the GaN/AlGaN epitaxial layers. QST® enables breakage-free high-volume manufacturing of standard semi-spec thickness 200mm GaN device wafers (scalable to 300mm), covering all GaN applications including 100V-to-1800V high performance power devices, RF devices, and display microLEDs.

In this talk, the following status updates on 200mm QST®-based materials and device technologies will be presented: (1) commercial QST® substrate products, (2) commercial GaN-on-QST® epi-wafer products, including development studies on epi-wafers for 1,200V and beyond applications, (3) high-performance normally-off 650V p-GaN based GaN-on-QST® HEMT transistors & monolithic ICs (with integrated drivers and logic) fabricated in a CMOS fab and commercialization timelines, (4) 200mm GaN-on-QST® device foundry services for the industry players, and (5) initial high-performance GaN-on-QST® RF device results.
An Investigation of the Recovery of Silicon Photovoltaic Cells By Application of an Organic Solvent Method
Authors: Subramanian Vaidyanathan , Tembo Prichard , Heninger Milan
Published: December 2020

The issue surrounding the treatment of photovoltaic (PV) waste is one that is gaining traction around the world. The recovery of valuable materials from end-of-life, damaged and out-of-spec PV modules is one PV waste treatment approach that has been investigated. However, this approach usually involves damage to PV cells that could otherwise be reused if extracted undamaged as the lifetime of PV cells is far longer than that of PV modules. Current practice is mainly focused on extracting the elemental constituents such as silver, copper and aluminum as well as recycling of silicon to be used in the fabrication of new PV cells. A method of extracting undamaged PV cells would address PV module waste generation with the added advantage of further reducing the carbon footprint associated with PV module manufacturing. This study will focus on the recovery of undamaged silicon PV cells from end-of-life PV modules by application of an organic solvent method. Specific organic solvents deemed to be appropriate for the recovery process along with operating conditions allowing for the recovery of undamaged PV cells from end-of-life PV modules are investigated. Herein, we compared the proposed PV cell recovery method with current recycling techniques which result in damage to PV cells. Furthermore, we will demonstrate that a comparison based on surface morphology and electrochemical properties between the recovered and virgin PV cells shows that the recovered PV cells could effectively be used in the fabrication of new PV modules.
(Invited) Dye-Sensitized Photo Rechargeable Battery for Indoor Applications
Authors: Kwon Tae_Hyuk
Published: December 2020

Dye-Sensitized Solar Cells (DSSCs) have great potentials owing to their aesthetic colors, transparency and low cost. Furthermore, they are favorable for indoor system, because DSSCs have great power conversion efficiency (PCE) at low light. However, there are still several problems in the practical applications. Therefore, our group suggested the new concepts of organic materials and devices for approaching to real application. For this aim, we developed dye-sensitized photo rechargeable solar battery for indoor light saving.

Until now, most of single-structured photo-rechargeable devices considered photo-charging process at high light intensity (mainly standard AM 1.5G sunlight). Furthermore, it is very difficult to combine dye-sensitized solar cells with lithium ion battery in a monolithic device because of their intrinsic mismatch energy levels of photo (-0.5 V vs NHE) and storage electrode (-3.0 V vs NHE). We came up with this intrinsic issues by using the overlithiation reaction of LiMn2O4 (ca. 0.0 V vs NHE) for energy storage and finally, achieved self-powered dye-sensitized photo rechargeable battery (DSPB, FTO/TiO2/Dye/Redox mediator/Pt-Li+ conducting separator/Li+ solution/ LixMn2O4) in monolithic devices, and suggested new concepts for energy recycle of indoor lightening. Next, we investigated the light intensity dependence of photo-charged energy density with different redox mediator (or charge regenerator for oxidized dye), such as I−/I3
−, Co2+/3+(bpy)3, Cu+/2+(dmp)2. Finally, the DSSBs were successfully working at low light intensity (11.5% of ηoverall at 0.15 mW cm−2 (500 lux)), operating the commercial IoT wireless sensor node using only indoor light sources.
Effect of SrF2:Pr3+-Yb3+ Nanophosphor on Downconversion of High Energy Photons for Efficient Dye-Sensitized Solar Cells
Authors: Kaliamurthy Ashok Kumar , Lung Quang Nhat Dang , Yoo Kicheon , Lee Jae-Joon
Published: December 2020

An emerging important class of photovoltaics for the next generation, the dye sensitized solar cells (DSSCs) has attracted great attention due to its low-cost, simple fabrication process and good performance. Though, one of the major loss mechanisms leads to lowering the power energy conversion efficiency is thermalization of charge carriers generated by the absorption of high energy photons. One promising novel strategy to decrease such thermalization loss is the use of downconversion (DC) luminescent materials as spectral converters. The rare-earth doped downshifting materials can converts higher energy photons into lower energy photons based on energy transfer from lanthanide ions to Yb3+ ions. In addition, the downconversion nanoparticles (DCNPs) are also act as scattering centers which can facilitates the light capture in photo-absorbing layer. With this aim, the rare earth doped downconversion SrF2: Pr3+-Yb3+ nanoparticles were synthesized by facile template free hydrothermal method. X-ray diffraction analysis confirms the formation cubic SrF2 phase. The prepared SrF2: Pr3+-Yb3+ down-shifting nanophosphor shows strong absorption in UV region and broad luminescence band emission in visible region evidenced from absorption and photoluminescence studies respectively. The enhancement in power conversion efficiency (PCE) was achieved by employing the synthesized downconverting nanomaterial as bottom layer in DSSC photoanode (Fig.1). The photovoltaic performance of the device was studied using standard solar simulator at 1 Sun intensity (AM 1.5 G) and DSSC with SrF2: Pr3+-Yb3+ shows improved efficiency of 9.066% than bare TiO2 based device (8.395%). The down-shifting nanophosphor material enhanced the efficiency of DSSC by 7.4% with 7.5% increment in photocurrent density compared to bare TiO2 based device.

Figure 1
High Efficiency PbS Quantum Dot Solar Cell with Reduced Hysteresis Using Transfer Printing
Authors: Shim Hyung Cheoul , Song Jung Hoon , Hyun Seungmin , Jeong Sohee
Published: December 2020

We fabricated a hole transport layer (HTL) using transfer printing to fabricate high efficiency PbS quantum dot solar cell with minimized hysteresis. We applied PbS-EDT(1,2-ethanedithiol) as an HTL and controlled the adhesive properties between the donor substrate and the HTL through the UVO process in order to effectively transfer the HTL to the PbS layer, which enabled multilayer transfer printing as a result. During the transfer printing process, a gradient solid-solution layer was created at the interface with the existing PbS layer to reduce the hysteresis phenomenon, and to improve the power conversion efficiency to about 10% according to the HTL thickness optimization. In addition, the use of the EDT solvent can be remarkably reduced by using the transfer printing when forming the PbS-EDT layer. This can reduce the amount of organic solvent consumed in the process and improve the potential of environmentally friendly processes.
Development of Blocking Layer Paste for Making Module By Screen Printing Procedure
Authors: Kang Hyeong Cheol , Yoo Kicheon , Yang Jae Geun , Lee Jae-Joon
Published: December 2020

Dye Sensitized Solar Cells(DSSCs) is the next generation solar cell that has various advantages different from existing solar cells such as high transmittance, various colors, and High PCE in low light. Building Integrated Photovoltaic (BIPV) is getting a lot of attention by using DSSCs. The blocking layers in DSSCs improve the adhesion between the conductive substrate and the semiconductor electrode, and also reduce the recombination and back reaction by prevent the loss of electrons generated by light. In general blocking layer solution;TiCl4 dip coat, is used for making unit cells. However, in the large-area module manufacturing process, the solution process is not suitable. In addition, screen printing is applied by pasting the blocking layer material rather than the conventional solution process because selective coating is necessary for the part that does not need blocking layer such as Ag grid of Z-type module or Pt electrode part of W-type module. In this study, we developed the blocking layer paste, which enables a large-area screen printing process with a higher transparent(77.6%) than the TiCl4 dip coating(71.1%) / spin coating method(74.8%) by controlling Ti precursor/vehicle. Through these studies, it can be used not only the application of large area modules but also replacing exist unit cell solution processes (TiCl4 dip coat, etc.).
Appropriate Electron Transport Layer for Highly Efficient Organic Photovoltaics Under Low-Intensity Light Conditions
Authors: Baek Seunghun , Ko Doo-Hyun
Published: December 2020

Inverted organic photovoltaics (OPVs) have been studied due to the low stability in conventional structure. For the inverted OPVs, insertion of electron transport layer (ETL) between the photoactive layer and cathode is essential to improve the power conversion efficiency ,and the metal oxide (e.g. ZnO) and conjugated polyelectrolyte have been widely used . In most studies, optimization and mechanism analysis have been focused under AM 1.5 sun condition. However, the working mechanism of OPVs varies depending on the light intensity, and thereby further understanding on the function of ETL needs to optimize OPVs performance under low-intensity light including indoor conditions. In this study we demonstrate that ZnO provides better performance as well as reproducibility compared with a conjugated polyelectrolyte ETL regardless of the light intensity. In addition, appropriate ETL material should afford excellent charge selectivity and effective coverage of the bottom ITO surface to prevent shunt site formation, which enables the development of highly efficient OPVs under low-intensity light including indoor conditions.
Ternary Organic Semiconductor Blend for High Photovoltaic Performance Under Both Indoor and Outdoor Operating Conditions
Authors: Lee Chi-Hyeong , Ko Doo-Hyun
Published: December 2020

Ternary blend in Organic Photovoltaics (OPVs) have been known as a way to increase performance in both low light intensity and AM 1.5G conditions. We have conducted a comparative study on 2 Donors:1 Acceptor (2D:1A) blends and 1 Donor:2 Acceptors (1D:2A) blends; 1D:2A blends have the higher performance and thermal stability than 2D:1A blends. In particular, non-fullerene acceptor (NFA) used for the 1D:2A blends have a good effect on packing property and crystallinity. The 1D:2A with optimized morphology reduced charge recombination on various irradiation conditions while the efficiency of 2D:1A devices depends on the fluorescence resonance energy transfer mechanism. The synergistic effect of 1D:2A blend with NFAs secures better efficiency and sustainable photoelectric properties under both indoor and outdoor operation conditions. Our analysis of the experiments reveals that NFA optimizes the arrangement of molecules to build more efficient ternary bulk heterojunctions in 1D:2A blends. Finally, the optimized ternary OPVs show effectively high power conversion efficiency of over 25% in both 200 lux and 1000 lux light–emitting diode conditions and present new opportunities in various practical applications.
Investigation of Triple Cation Organo-Metal Halide Perovskite Solar Cells
Authors: Kim Gisung , Kim Mijoung , Kim Moonhoe , Shin Jaekwon , Oh Juyoung , Park Geon , Yang JungYup
Published: December 2020

Organic–inorganic hybrid halide perovskites have attracted considerable attentions due to their impressive photovoltaic properties. Record efficiencies in perovskite solar cells (PSCs) have been achieved using as the absorber material a multiple cation/anion perovskite mixing not only methylammonium (MA) and formamidinium (FA), but also the cesium (Cs) cation and iodine (I) and bromine (Br) as anions, materials that have demonstrated good long-term stability. In this study, we have investigated triple cation engineering to improve the quality of the absorber layer through some substitution of formamidinium (FA) and cesium (Cs) for the methylammornium (MA) cation site. The perovskite absorber layer of CsFAMAPb(IBr)3 was fabricated by one-step spin coating method. One of the important things in one-step spin coating towards to obtain high quality CsFAMAPb(IBr)3 layer is an anti-solvent engineering which is dripping to the anti-solvent during spin coating of CsFAMAPb(IBr)3. The properties of CsFAMAPb(IBr)3 absorber layer were found to be strongly influenced by the amount, dispensing speed, and time to spray of anti-solvent solution. Chlorobenzen was used as an anti-solvent solution. The result that the CsFAMAPb(IBr)3 layer appropriately sprayed with chlorobenzen is beneficial to film quality and device efficiency because the nucleation of CsFAMAPb(IBr)3 layer was affected by the anti-solvent engineering, which affected the film crystallite, density, and surface morphology. The CsFAMAPb(IBr)3 layer by optimized 0.3 mL amount of chlorobenzen, 1.28 mL/sec dispensing speed, and 15 second (time to spray after spinning) showed the best efficiency of above 20 % with reproducibility.

This research was also supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2019R1A2C4070248).
Amorphous IGZO TFTs with Low Electrical Hysteresis By Using Two-Photomask Process
Authors: Li Zhen-Hao , Chiang Tsung-Che , Liu Po-Tsun , Kuo Yue
Published: December 2020

Amorphous oxide semiconductor (AOS)-based TFTs have been considered as potential channel materials for high-resolution TFT-LCDs and AMOLEDs [1-3]. However, the electrical characteristics of AOS TFTs frequently deteriorate with increasing operating cycle times because of the increased trap states present in the AOS semiconductor layer. In this work, we demonstrated the amorphous Indium-Gallium-Zinc-oxide (a-IGZO) TFT fabricated by using two-photomask process [4], which can effectively reduce the process complexity and manufacture cost.

Experiment

The TFT manufacture processes are as followed. A Mo film was deposited by DC sputtering on glass substrate as gate electrode. After patterning, the tri-layer structure of HfO2 /IGZO/ HfO2 film was deposited as gate insulator, channel and passivation layer respectively. The pattern of channel and passivation layer was defined by photolithography with back exposure. Finally, using DC sputtering deposited the MO films and patterned to form the source/drain electrode.

Result and Discussion

In this work, experimental results have shown that the 2-photomask fabricated a-IGZO TFT can exhibit superior performance with a subthreshold swing of 66 mV/dec., threshold voltage of -0.37V, field effect mobility of 10 cm2/V∙S, Ion/Ioff current ratio of ~107 and extremely low electrical hysteresis loop ∆V=10mV was obtained. The reliability of a-IGZO TFTs also was measured and investigated, it reveals the great reliability because the passivation layer can effectively isolate the reaction between the back-channel and atmosphere. It is highly promising to be applied for the emerging transparent display backplane technologies.

Reference

[1] K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, nature, vol. 432, no. 7016, pp. 488-492, 2004.

[2] J. Yao, N. Xu, S. Deng, J. Chen, J. She, H.P. D. Shieh, P.T. Liu, and Y.P. Huang, IEEE Transactions on Electron Devices, vol. 58, no. 4, pp. 1121-1126, 2011.

[3] P.Y. Kuo, C.M. Chang, I.H. Liu, and P.T. Liu, Scientific reports, vol. 9, no. 1, pp. 1-7, 2019.

[4] Y. Kuo, Journal of The Electrochemical Society, vol. 138, no. 2, pp. 637, 1991.

Figure 1
Effect of Glass Substrate on the Film Properties of Poly Silicon by Excimer Laser Annealing
Authors: Zhu Bin , Vaddi Rajesh , Huang Ming-Huang , Kim Hoon , Manley Robert G.
Published: December 2020

This work studies the effect of glass substrate thermal properties on the crystallization behavior and surface topography of polycrystalline silicon (poly-Si) films formed by a XeCl excimer laser annealing of amorphous silicon. Films of 60 nm hydrogenated amorphous silicon (a-Si:H) film were deposited on different glass substrates of varying thermal properties. A 500 nm SiO2 buffer layer was in between the glass and the silicon film. The silicon was crystallized by a XeCl excimer laser. The atomic force microscopy (AFM) and in-plane X-ray diffraction (IPXRD) were used to evaluate the surface topography, the surface roughness, and crystalline in-plane orientation of poly-Si, respectively. Grazing incidence X-ray diffraction (GIXRD) was employed to quantify the residual stress in poly-Si film. The film properties of poly-Si exhibit a small relationship with the glass thermal properties. The higher thermal conductivity of glass retards the poly-Si <111> texture and reduced the residual tensile stress. The higher thermal diffusivity of the glass causes a decline in the poly-Si <111> texture, the surface asymmetry and flatness. A light shield introduced between glass and buffer layer in the low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) structures, further weakens the impact of the glass substrate on excimer laser annealing (ELA) poly-Si properties.
New Degradation Model of LTPs TFT Aged Off-State Bias Stress on Flexible Substrate
Authors: Kim Kihwan , Kim Soonkon , Song Minjun , Kim Hyojung , Kim Yongjo , Choi Byoung Deog
Published: December 2020

We conducted experimental and quantitative studies on the effects of off-state bias stress of the p-type polycrystalline silicon thin film transistors (TFTs) on flexible substrate and presented a new degradation model using TCAD simulation. In the off-state bias stress condition, the gate induced drain leakage (GIDL) current is determined by the gate and drain voltage (Vgd) and gate bias stress above a certain bias is accompanied by a change in Vth. To understand and model the underlying mechanism of these results, we developed a spatial probability analysis model with mapping of physical quantity (SPAM). The spatial distribution the E-field and the electron concentration are considered as degradation factors, and are used in the equations for defect creation (DC) and charge trapping (CT) TCAD model. We had to implement different forms of aging model in the two regions: 1) CT in poly-Si/SiOX interface, and 2) DC in the channel bulk (especially, the grain boundary). Finally, our new degradation model allows us to analyze how the GIDL current decreases with various aging conditions and provides a quantitative relationship between the amount of charge trapping and the amount of defect creation

I. Fixed negative charge (-) of interface of poly-Si/SiOx

(ε(x,y) > εC,f and n(x,y)> nC,f)

Qfix
(-) (x,y)=αf *[{ε(x,y)-εC,f}/εm,f ]γf_field
*[log{n(x,y)/nC,f }]γfn

II. Ionized defect density of channel bulk (Grain and GB)

(ε(x,y,z) > εC,tA )

NtA
(-) =gtA (ε)*exp[-{(EtA-EGA)/WGA}2 ]

gtA (ε)= αtA*[{ε(x,y,z)-εC,tA}/εm,tAm ]γtA

Figure 1