Performance Of Various Devices Research Articles

Hole transport layer selection toward efficient colloidal PbS quantum dot solar cells.

The effect of energy level alignment between the hole transport layer (HTL) and active layer in PbS quantum dot (QD) solar cells was investigated. Here, a great variation in device performance was observed when employing different hole transporting materials. Devices using HTLs that could not block electrons only show poor device behaviors, while those employing wide band-gap hole transporting materials with shallow lowest unoccupied molecular orbital (LUMO) energies to block electrons exhibit reduced dark currents as well as enhanced device efficiencies. A power conversion efficiency of 4.4% was obtained by utilizing Poly-TPD as the HTL due to the optimized energy level alignment. These improvements were realized by preventing current leakage and consequent counter diode formation. The efficiency can be further improved to 4.9% by inserting EDT-treated PbS QD film (PbS-EDT) hole transporting materials with higher hole mobility as well as suitable energy levels that can increase the collection efficiency.

Organic Solar Cells Based on Non-Fullerene Small-Molecule Acceptors: Impact of Substituent Position

Molecular engineering of non-fullerene small-molecule acceptors (SMAs) plays a key role in enhancing the performance of organic solar cells. An effective strategy is to introduce functional groups into SMA end-groups to tune the electronic and morphological properties of polymer/SMA blends. Here, molecular dynamics simulations and long-range corrected density functional theory calculations are combined to examine the impact of the position of methoxy substitution in the SMA end-groups. As representative systems, blends of the IT-OM small-molecule acceptor with the PBDB-T polymer donor are explored; three different positions of the methoxy substitution of the IT-OM end-groups are examined. By considering intermolecular mixing and packing, the energetic distribution of the charge-transfer electronic states, the exciton dissociation and nonradiative recombination processes, and the electron-transfer rates among adjacent acceptors, we provide a comprehensive molecular-scale rationalization of the significant experimental variations in device performance for PBDB-T/IT-OM-based solar cells as a function of methoxy position.

Enhanced Optimal Multi-Row Detailed Placement for Neighbor Diffusion Effect Mitigation in Sub-10 nm VLSI

Layout-dependent effect causes variation in device performance as well as mismatch in model-hardware correlation in sub-10 nm nodes. In order to effectively explore the power-performance envelope for IC design, cell libraries must provide cells with different diffusion heights, leading to neighbor diffusion effect (NDE) due to inter-cell diffusion height change (diffusion steps ). Special filler cells can protect against steps to functional cells, but with nontrivial area overhead. In this paper, we develop dynamic programming (DP)-based single-row and multi-row (MR) detailed placement optimizations that optimally 1 reduce inter-cell diffusion steps to mitigate the impacts of NDE. Compared to previous works, our algorithms are capable of exploring richer solution spaces as they support cell flipping, relocating, and reordering across cell rows; we also consider cell displacement, flipping, and wirelength costs. Notably, to our knowledge, our MR DP-based optimization algorithm is the first to optimally handle inter-row cell relocating and reordering. We also explore various metaheuristic configurations to further improve the solution quality. Last, we develop a timing-aware approach, which is capable of creating intentional steps that can potentially improve the drive strength of critical cells. 1 The optimality is in terms of maximum diffusion step reduction, for given displacement range, reordering range and cell variants. Additionally, the above range definitions, including the definition of the ordering of cells, depend on assumptions described in Sections IV and V .

Precise Control of Poly-Silicon Height by Plasma Etching in FinFET Technology Node

In this paper, a holistic methodology for the dummy poly silicon height control is discussed, including within shot, within wafer, and wafer to wafer in IC mass production. With a certain process and integration control, the poly-silicon height can be precisely controlled, which is beneficial to the final metal gate height. The poly-silicon height can achieve a less than 2% variation within wafer. The variation of device and yield performance is hence much improved.

Review Article: Crystal alignment for high performance organic electronics devices

Organic electronics devices based on high-performance small-molecule organic semiconductors have gained substantial attention because of their unique advantages such as excellent charge transport, solution processability, and environmental stability. However, the intrinsic crystallization of small-molecule organic semiconductors is anisotropic, resulting in significant device performance variations of organic electronics devices. In this article, the authors review the various approaches and techniques developed to control and align the crystallization of some benchmark solution-processable, high-performance, small-molecule organic semiconductors, such as 6,13-bis(triisopropylsilylethynyl) pentacene, N,N′-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide, and 5,11-bis(triethylgermylethynyl)anthradithiophene. These alignment approaches are studied in the context of capillary force-based techniques, patterning-based techniques, solution-shearing-based techniques, and other miscellaneous techniques, including zone-casting, vertical flowing, air flow navigation, temperature gradient alignment, etc. The organic semiconductors and crystal alignment techniques reviewed in this article shed light on important relationship among crystallization, charge transport, and device performance and can be applied to various high-performance organic electronics devices, such as organic thin film transistors and solar cells.

Temperature-dependent Electrical Characterization of Single and Dual-gate Flexible Carbon Nanotube Thin Film Transistors

Dual-gate carbon nanotube thin film transistors (CNTTFTs) with hafnium dioxide (HfO2) and silicon dioxide (SiO2) as gate dielectrics and single-gate CNTTFTs of two types both of bottom-gate structure but one with HfO2 as gate dielectric and another with SiO2 as gate dielectric were fabricated on a flexible polyimide substrate using a scalable process. Electrical characteristics of the fabricated devices at elevated temperatures varying from 25 to 120°C were investigated and compared. Both single and dual-gate flexible devices have exhibited p-type characteristics. As the temperature was raised the on-current, off current, subthreshold swing, transconductance and drain conductance of both single and dual-gate devices increased whereas on–off current-ratio and threshold voltages decreased. The devices exhibited deterioration in transconductance and on-current with the increase of channel lengths. The present work illustrates that dual-gate flexible CNTTFTs outperform the single-gate flexible CNTTFTs in all electrical characteristic parameters and have shown the highest gate control over the channel at different temperatures varying from 25 to 120°C. The performance variations of both single and dual-gate flexible devices were less than 3.1% till the temperature of 50°C and were operational as CNTTFTs at temperatures varying from 25 to 120°C. The on–off current ratio, subthreshold swing, and threshold voltages deteriorate highly at temperatures higher than 120°C and also it was investigated that electrical characteristics were not repeatable at temperatures higher than 120°C. The CNTTFTs on the flexible substrate can be used for flexible electronics applications till 120°C.

Visualizing Nonradiative Mobile Defects in Organic–Inorganic Perovskite Materials

AbstractOrganic–inorganic perovskite materials have mobile charged point defects that migrate in response to voltage biasing and illumination, causing device performance variation over time. Improvements in device stability and reliability require methods to visualize point defect migration, estimate ionic mobilities, and identify factors influencing their migration. In this work, a versatile method is demonstrated to track nonradiative point defect migration in situ. Photoluminescence mapping of laterally biased perovskite films is used to track continuous changes in nonradiative recombination as charge‐trapping defects migrate between the device electrodes. A Monte Carlo framework of defect drift and diffusion is developed that is consistent with experimental photoluminescence observations, which combined enables point defect mobility estimation in methylammonium lead iodide films. Furthermore, measurements performed on materials with varied grain sizes demonstrate that point defect mobility is 1500× faster at grain boundaries compared to bulk. These findings imply that grain morphology can be used to tune point defect mobility such that large‐grained or single‐crystal materials inhibit point defect migration. The methods used in this work can be applied to visualize and quantify the migration of charge‐trapping point defects in a wide range of state‐of‐the‐art perovskite materials targeted toward reduced ionic mobilities and superior device stability.

Hardening, Softening, and Linear Behavior of Elastic Beams in MEMS: An Analytical Approach

This paper investigates different topologies of springs used to couple the orthogonal translational motion of proof masses in Micro-Electro-Mechanical Systems (MEMS). This type of coupling is a key issue, since the dynamic response, and hence, the performance of various devices (e.g., MEMS gyroscopes) critically depends on the mechanical behavior of such deformable components. We first analytically investigate the problem through a model based on a modified second-order Timoshenko beam theory developed for both compact and built-up section beams. Its predictions inspire the design of three test structures, whose purpose is to highlight, through different spring topologies, the transition from a hardening behavior to a softening behavior, with possible intermediate optimum conditions for linear response at large displacements. The structures are characterized in detail, with variable forced displacements at resonance (25 kHz) up to about $10~\mu \text{m}$ . Experiments validate the model predictions in all the considered situations. [2018-0181]

Synthesis of peripherally tetra substituted neutral azophenoxy zinc phthalocyanine and its application in bulk hetero junction solar cells

Neutral zinc phthalocyanine bearing 4-phenylazopohenoxy group at the periphery (ZnPc-4) has been synthesized from zinc acetate dihydrate Zn(CH3COO)2·2H2O and 4-(phenylazophenoxy)phthalonitrile. The synthesized zinc phthalocyanine ZnPc-4 was characterized using UV–visible, FTIR, 1H NMR and MALDI-TOF mass spectral measurements. Solution processed bulk hetero junction solar cells were fabricated using ZnPc-4 as the donor material and [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) as the acceptor material. A power conversion efficiency of 0.69% was achieved by optimizing the donor:acceptor weight ratio. Variation in device performance with the donor:acceptor weight ratio was investigated using atomic force microscopy.

Piezotronic effect on interfacial charge modulation in mixed-dimensional Van der Waals heterostructure for ultrasensitive flexible photodetectors

Van der Waals (vdWs) heterostructure is emerging as one of the most interesting systems in next-generation flexible optoelectronics. Furthermore, the gate-tunability of vdWs heterostructure is widely applied to enhance the performance of various devices, which is generally achieved by external electric field. However, in-plane cracking and slippage of gate electrode restricted this external electric field modulation in flexible devices. Here, we propose a distinctive strain-gating method to manipulate 2D WSe2-1D ZnO vdWs interfacial charge and modulate its photosensing performance by tuning electronic states of WSe2. With increasing tensile strain, the device shows obvious enhancing photocurrent and the corresponding photoresponsivity reaches up to 394 mA W−1 under white light illumination. Such performance enhancement can be attributed to strain-induced piezopolarization charges on ZnO nanobelt polar surface, which function as "gate" to tune the local transport of photogenerated carriers at the WSe2-ZnO vdWs interface. This work provides a new strategy to achieve interaction between vdWs interface and strain stimuli, which broadens applications of functional vdWs heterostructure for next-generation photodetection or imaging.

Performance Evaluation of a Recognition System on the VLIW Architecture by the Example of the Elbrus Platform

This paper overviews modern computing devices based on the Elbrus VLIW architecture and presents experimental results for the performance evaluation of the Smart IDReader document recognition system on these devices. Methods for speeding up the recognition system on the Elbrus platform are described, experimental estimates of the speedup improvements are presented, and the performance of various devices based on Elbrus processors is compared.

In-plane-gate flexible single-crystalline silicon thin-film transistors with high-k gate dielectrics on plastic substrates

Flexible single-crystalline silicon in-plane-gate thin-film transistors (TFTs) with high-k gate dielectrics on plastic substrates have been demonstrated in this letter. The high-k Nb2O5-Bi2O3-MgO (BMN) ceramic has been deposited as gate dielectric layer by magnetron sputtering at room temperature. ∼200 nm Si nanomembrane as the device active layer has been transferred onto the flexible substrates. An in-plane-gate structure has been employed for the flexible TFTs, to achieve high control ability and low leakage current. The flexible TFT demonstrates ∼106 on/off ratio, ∼230 cm2v-1s-1 electron field effect mobility, and only ∼nA leakage current. The capacitances of the in-plane-gate structure are measured and analyzed to better understand the channel control mechanism of the flexible TFTs with high-k gate dielectrics. Mechanical bending tests have been conducted and the underlying mechanism for the device performance variations has been discussed. The flexible TFTs show great potential for the applications in high performance, large area and high integrated flexible circuits.

Large-Scale Alignment of Polymer Semiconductor Nanowires for Efficient Charge Transport via Controlled Evaporation of Confined Fluids.

Long-range alignment of conjugated polymers is as critical as polymer chain packing for achieving efficient charge transport in polymer thin films used in electronic and optoelectronic devices. Here, the present study reports a facile, scalable strategy that enables the deposition of macroscopically aligned polymer semiconductor nanowire (NW)-array films with highly enhanced charge carrier mobility, using a modified controlled evaporative self-assembly (MCESA) technique. Organic field-effect transistors (OFETs) based on highly oriented poly(3-hexylthiophene) (P3HT)-NW films exhibit more than 10-fold enhancement of carrier mobility, with the highest mobility of 0.13 cm2 V-1 s-1, compared to the OFETs based on pristine P3HT films. Significantly, large-area aligned P3HT NW-films, which are deposited over 12 arrays of transistors on a 4 in. wafer by an MCESA coating, result in lower device performance variation (i.e., standard deviation ≈ ±0.0172 (16%) cm2 V-1 s-1) as well as an excellent average device performance (i.e., average charge mobility ≈ 0.11 cm2 V-1 s-1), compared to those obtained using the conventional CESA coating, overcoming a critical challenge in the field of OFETs.

Microcrystalline silicon thin film deposition from silicon tetrafluoride: Isolating role of ion energy using tailored voltage waveform plasmas

The energy of ions during plasma enhanced chemical vapor deposition (PECVD) is known to impact material quality, but isolating this effect from other process parameters (plasma density, pressure) in a capacitively coupled plasma (CCP) is not straightforward. In this work, we utilize a novel radio-frequency (RF) excitation technique – tailored voltage waveforms (TVW) – as a solution to achieve ion flux-energy decoupling through the electrical asymmetry effect. This makes it possible to independently study the impact of ion energy on material deposition. We study the impact of ion energy - more precisely the maximum ion bombardment energy (IBEmax) before collisions - on the PECVD of hydrogenated microcrystalline silicon (µc-Si:H) thin films from an SiF4/H2/Ar chemistry. Through structural and electronic analysis, we find that the variation of IBEmax directly translates into material quality, even at relatively high process pressure. Better material properties (crystalline grain features, material density and photoelectronic response) are obtained for films deposited with moderate values of IBEmax around 45–55 eV. Above this range, a deterioration in material quality is observed, presumably due to more effective bulk atomic displacements induced by the silicon-containing ions. These results are consistent with the performance of single-junction µc-Si:H solar cell devices using these materials as active layers. Optimum performance is obtained for devices with an absorber layer deposited using a plasma excitation resulting in IBEmax in the range of ~45–55 eV. The variation in device performance is mainly due to changes in the open circuit voltage.

Merits and Challenges of Ruddlesden-Popper Soft Halide Perovskites in Electro-Optics and Optoelectronics.

Following the rejuvenation of 3D organic-inorganic hybrid perovskites, like CH3 NH3 PbI3 , (quasi)-2D Ruddlesden-Popper soft halide perovskites R2 An -1 Pbn X3 n +1 have recently become another focus in the optoelectronic and photovoltaic device community. Although quasi-2D perovskites were first introduced to stabilize optoelectronic/photovoltaic devices against moisture, more interesting properties and device applications, such as solar cells, light-emitting diodes, white-light emitters, lasers, and polaritonic emission, have followed. While delicate engineering design has pushed the performance of various devices forward remarkably, understanding of the fundamental properties, especially the charge-transfer process, electron-phonon interactions, and the growth mechanism in (quasi)-2D halide perovskites, remains limited and even controversial. Here, after reviewing the current understanding and the nexus between optoelectronic/photovoltaic properties of 2D and 3D halide perovskites, the growth mechanisms, charge-transfer processes, vibrational properties, and electron-phonon interactions of soft halide perovskites, mainly in quasi-2D systems, are discussed. It is suggested that single-crystal-based studies are needed to deepen the understanding of the aforementioned fundamental properties, and will eventually contribute to device performance.

Stable and Reversible Triphenylphosphine-Based n-Type Doping Technique for Molybdenum Disulfide (MoS2)

A highly stable and reversible n-type doping technique for molybdenum disulfide (MoS2) transistors and photodetectors is developed in this study. This doping technique is based on triphenylphosphine (PPh3) and significantly improves the performance of MoS2 transistor and photodetector devices in terms of the on/off-current ratio (8.72 × 104 → 8.70 × 105), mobility (12.1 → 241 cm2/V·s), and photoresponsivity ( R) (2.77 × 103 → 3.92 × 105 A/W). The range of doping concentrations is broadly distributed between 1.56 × 1011 and 9.75 × 1012 cm-2 and is easily controlled by adjusting the temperature at which the PPh3 layer is formed. In addition, this doping technique provides two interesting properties that have not been reported for previous molecular doping techniques: (i) high stability leading to small variations in device performance after exposure to air for 14 days (on-current: 1.34% and photoresponsivity: 1.58%) and (ii) reversibility enabling the repetitive formation and removal of PPh3 molecules (doping and dedoping).

Comparison of processing windows and electronic properties between CH3NH3PbI3 perovskite fabricated by one-step and two-step solution processes

Abstract Despite the rapid progress in device efficiency of the perovskite solar cells (PVSCs), the origin of commonly observed large variability of device performance from one-step to two-step approaches is still elusive. Herein, the processing windows of perovskite films prepared by one-step and two-step processes have been investigated. We find that both perovskite films prepared by one-step and two-step methods in air are much rougher than that prepared in glovebox. For the one-step method, complete perovskite conversion can be readily achieved both in air and in glovebox, but totally different in surface morphology. For the two-step method, residual PbI2 are remained in perovskite film, particularly with larger amount for the film prepared in air. Both rough surface and incomplete conversion hinder the realization of high quality perovskite film in air. The photovoltaic performances of the PVSCs prepared by one-step and two-step methods in glovebox are systematically compared. The generally observed lower photovoltaic performance of two-step PVSCs is ascribed to the additional trap-assisted recombination process due to larger trap density in the two-step perovskite film. This is confirmed by carrier recombination study using steady state photoluminescence, transient photovoltage and photocurrent measurements. Finally, combining the high work function hole transporting material poly-TPD, and the high-quality one-step perovskite film, a 17.5% high-efficiency PVSCs can be achieved. The results reveal the major impacts on the morphological and electronic properties of perovskite films between one-step and two-step method, and it brings insight into the strategy for extending the processing windows to achieve highly reliable PVSCs.

Channel-restricted meniscus self-assembly for uniformly aligned growth of single-crystal arrays of organic semiconductors

A channel-restricted meniscus self-assembly (CRMS) method is developed for wafer-scale, highly uniform, aligned growth of organic semiconductor single crystals (OSSCs). Field-effect transistors (FETs) made from the OSSC arrays exhibit a high average mobility of up to 30.3 cm 2 V −1 s −1 with good uniformity among devices. This method is general for the growth of various OSSC arrays, facilitating the applications of OSSCs in large-area, high-performance organic electronic devices. Organic semiconductor single-crystal (OSSC)-based field-effect transistors (FETs) with high mobility and small device-to-device variation enable OSSCs to be adapted for practical applications. Research attention has recently been focused on developing simple ways of fabricating large-area OSSC arrays by means of solution-coating techniques. However, the lack of control of the meniscus front, where the nucleation and growth of organic crystals occur, leads to inconsistent crystal alignment and consequently induces large variation in device performance. Here, we propose a universal strategy, termed the channel-restricted meniscus self-assembly (CRMS) method to fabricate ultrahigh-mobility, uniform OSSC arrays. The microscale photoresist channels used in this method produce a confinement effect to reduce the size of the meniscus, enabling the homogeneous nucleation of OSSCs at the meniscus front. Meanwhile, the dip-coating process ensures consistent molecular packing in the OSSCs and thus guarantees their highly uniform electrical properties. Using 2,6-diphenylanthracene as an example, wafer-scale (>2 inch) OSSC arrays with very small size variations (10%) are successfully prepared, which is very difficult to achieve by using the previously reported methods. As a result, field-effect transistors (FETs) based on the OSSC arrays show a high average hole mobility of up to 30.3 cm 2 V −1 s −1 with good uniformity among devices. This method is general for the growth of various OSSC arrays, facilitating the applications of OSSCs in large-area, high-performance organic electronic devices.

Modulating Surface Morphology and Thin-Film Transistor Performance of Bi-thieno[3,4-c]pyrrole-4,6-dione-Based Polymer Semiconductor by Altering Preaggregation in Solution.

Due to their strong intermolecular interactions, polymer semiconductors aggregate in solution even at elevated temperature. With the aim to study the effect of this kind preaggregation on the order of thin films and further transistor performance, bi-thieno[3,4-c]pyrrole-4,6-dione and fluorinated oligothiophene copolymerized polymer semiconductor P1, which shows strong temperature-dependent aggregation behavior in solution, is synthesized. Its films are deposited through a temperature-controlled dip-coating technique. X-ray diffraction and atomic force microscopy results reveal that the aggregation behavior of P1 in solution affects the microstructures and order of P1 films. The charge transport properties of P1 films are investigated with bottom-gate top-contacted thin-film transistors. The variation of device performance (from 0.014 to 1.03 cm2 V–1 s–1) demonstrates the importance of optimizing preaggregation degree. The correlation between preaggregation degree and transistor performance of P1 films is explored.

Influence of dimensional variation of metal-insulator-metal stack in spectral response

Depending on the fabrication process and steps, dimensional and structural variation is generally expected during fabrication of plasmonic antenna arrays. It is important to know the critical design parameter and the effect of dimensional variation in device performance so as to predict experimental results. In this study we examine the effect of dimensional variation that could occur during fabrication of a metal-insulator-metal (MIM) patch antenna structure in its spectral response. The variation in width, edge roundness, stack slope, and slope of top metal layer are studied. We showed that the slope of the MIM stack (both dielectric and metal) plays an important role in determining the resonance peak while edge roundness of the stack layer severely affects the spectral width of periodically arranged differently sized patch antenna.