Reduction Of Hysteresis Research Articles

Impact of domains on the orthorhombic-tetragonal transition of BaTiO3 : An ab initio study

We investigate the multi-domain structures in the tetragonal and orthorhombic phases of BaTiO$_3$ and the impact of the presence of domain walls on the intermediary phase transition. We focus on the change in the transition temperatures resulting from various types of domain walls and their coupling with an external electric field. We employ molecular dynamics simulations of an ab initio effective Hamiltonian in this study. After confirming that this model is applicable to multi-domain configurations, we show that the phase transition temperatures strongly depend on the presence of domains walls. Notably we show that elastic 90$^{\circ}$ walls can strongly reduce thermal hysteresis. Further analysis shows that the change in transition temperatures can be attributed to two main factors - long-range monoclinic distortions induced by walls within domains and domain wall widths. We also show that the coupling with the field further facilitates the reduction of thermal hysteresis for orthorhombic 90$^{\circ}$ walls making this configuration attractive for future applications.

Experimentally correlating thermal hysteresis and phase compatibility in multifunctional Heusler alloys

Thermal hysteresis is recognized as one of the main drawbacks for cyclical applications of magnetocaloric and ferromagnetic shape memory materials with first-order transformations. As such, the challenge is to develop strategies that improve the compatibility between the phases involved in the transitions and study its influence on thermal hysteresis. With this purpose, we explore the thermal, structural, and magnetic properties of the ${\mathrm{Ni}}_{2}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}{\mathrm{Ga}}_{0.84}{\mathrm{Al}}_{0.16}$ Heusler alloys. The alloys present a thermal hysteresis reduction of \ensuremath{\sim}60% when the Cu content in the compound varies from $x=0.10$ to $x=0.25$, with a minimum hysteresis width of 6 K being achieved. We applied the geometric nonlinear theory of martensite to address the phase compatibility, quantified by the parameter ${\ensuremath{\lambda}}_{2}$, the middle eigenvalue of the transformation stretch tensor, and found that the minimum of hysteresis is associated with a better crystallographic compatibility (${\ensuremath{\lambda}}_{2}$ closer to 1) between the austenite and martensite phases. In addition, we show that the valleylike properties of hysteresis found in the ${\mathrm{Ni}}_{2}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}{\mathrm{Ga}}_{0.84}{\mathrm{Al}}_{0.16}$ compounds is present in several other alloys in the literature. These results provide pathways to understand as well as to master the phase compatibility and ultimately achieve a low thermal hysteresis in multifunctional Heusler alloys.

A universal method for hysteresis-free and stable perovskite solar cells using water pre-treatment

The power conversion efficiency (PCE) of organic–inorganic hybrid perovskite solar cells (PSCs) with SnO2 as an electron transport layer, achieve over 25%. However, the long-term stability and reduction of hysteresis are still great challenges. To solve these problems, different from the traditional treatment on ITO by UV or ozone, we introduce a simple, clean solvent engineering method of water spin-coating in the preparation of the SnO2 layer to obtain a compact and highly uniform SnO2 film. It is confirmed that after water treatment, the interface defects of the perovskite film are greatly reduced, and the electron transportation is also accelerated due to the near-perfect SnO2 layer. As a result, an improved PCE above 19% is obtained with triple cation (Cs/FA/MA)-mixed PSCs compared with ~16% PCE of the controlled devices. More importantly, the initial PCE of unwrapped PSCs with the water treatment can maintain 90% of their initial efficiency after exposure to ambient conditions for 360 h, while, the PSCs based on a conventional spin-coated SnO2 film degrade ~30%. Therefore, it is believe that this water spin-coating pre-treatment on SnO2 film we introduced can be a valid and practical method to obtain high-performance PSCs based on SnO2.

Hysteresis Reduction in Tunneling Magnetoresistive Sensor With AC Modulation Magnetic Field

A simple and practical ac modulation method to reduce the hysteresis in tunneling magnetoresistive (TMR) sensor is demonstrated. It is shown that with a suitable ac modulation magnetic field that is applied along the sensing direction of the TMR sensor, the hysteresis in the sensor can be reduced to a negligible level. Also, depending on the amplitude of the modulation field, the sensitivity and the dynamic range of the TMR sensor can be tuned to meet practical requirements in specific applications. The influence of the modulation on the noise of TMR sensor is also studied.

Hysteresis and current reduction during E–H mode transition in an inductively coupled plasma

A hysteresis loop has been observed during the E–H mode transition in an inductively coupled plasma at high pressures. The cause of the hysteresis has been reported as a nonlinearity of the transferred and dissipated powers due to capacitive coupling, multi-step ionization, the change in the electron energy probability function (EEPF), and so on [M. M. Turner and M. A. Lieberman, Plasma Sources Sci. Technol. 8(2), 313–324 (1999) and H. C. Lee and C. W. Chung, Sci. Rep. 5, 15254 (2015)]. However, when a coil current reduction is considered, the previous interpretation of hysteresis cannot explain the observations in the intermediate pressure region, where the coil current reduction occurs, but hysteresis is not observed. In this work, the E–H mode transition and its hysteresis are discussed in three pressure regions, the low, intermediate, and high pressure regions, whether or not the coil current and the hysteresis are observed. The power transfer efficiency, transferred power, EEPF, and total energy loss are obtained at 10, 100, and 300 mTorr. Hysteresis is only observed at 300 mTorr, and the coil current reduces at 100 and 300 mTorr during the E–H mode transition. The mechanism of hysteresis is explained in a power balance diagram that includes the transferred power and the dissipated power by considering the power transfer efficiency in the E and H modes. In addition, the conditions of hysteresis and coil current reduction are revealed and classified in this work.

Magnetocaloric effect in bamboo-grained Ni-Mn-Ga microwires over a wide working temperature interval

Bamboo-grained Ni-Mn-Ga microwire is promising for achieving considerable magnetic-field-induced strain due to less neighboring grain constraints to the twin boundary motion. Such reduction of resistance to interface motion also favors the reduction of hysteresis in magnetic refrigeration. Here, bamboo-grained Ni-Mn-Ga microwires were successfully synthesized by a melt-extraction technique and subsequent high temperature heat treatment at 1323 K for 3 h under Argon atmosphere. Corresponding microstructure, martensite transformation (MT) behaviors and magnetocaloric properties were investigated. The high specific surface area of the microwires favored the element evaporation at high temperature, leading to a heterogeneous composition state, which is responsible for the MT temperature (range) change and the multi-variants state in the bamboo-grained microwires. Nearly no magnetic hysteresis loss was obtained. The increased compositional variation led to the partial overlap of the MT and the magnetic transition, resulting in the improvement of the working temperature interval ~71 K and net refrigeration capacity ~255 J/kg under μ0H = 5 T, which is heretofore the largest value reported in Ni-Mn-based Heusler alloys. When utilized as refrigerant in a cooling device, such small-sized microwires can increase the contacting area between the material and the heat-transfer agent, which helps the heat exchange and thus improve the refrigeration efficiency.

Tailoring C60 for Efficient Inorganic CsPbI2 Br Perovskite Solar Cells and Modules.

Although inorganic perovskite solar cells (PSCs) are promising in thermal stability, their large open-circuit voltage (VOC ) deficit and difficulty in large-area preparation still limit their development toward commercialization. The present work tailors C60 via a codoping strategy to construct an efficient electron-transporting layer (ETL), leading to a significant improvement in VOC of the inverted inorganic CsPbI2 Br PSC. Specifically, tris(pentafluorophenyl)borane (TPFPB) is introduced as a dopant to lower the lowest unoccupied molecular orbital (LUMO) level of the C60 layer by forming a Lewis acidic adduct. The enlarged free energy difference provides a favorable enhancement in electron injection and thereby reduces charge recombination. Subsequently, a nonhygroscopic lithium salt (LiClO4 ) is added to increase electron mobility and conductivity of the film, leading to a reduction in the device hysteresis and facilitating the fabrication of a large-area device. Finally, the as-optimized inorganic CsPbI2 Br PSCs gain a champion power conversion efficiency (PCE) of 15.19%, with a stabilized power output (SPO) of 14.21% (0.09 cm2 ). More importantly, this work also demonstrates a record PCE of 14.44% for large-area inorganic CsPbI2 Br PSCs (1.0 cm2 ) and reports the first inorganic perovskite solar module with the excellent efficiency exceeding 12% (10.92 cm2 ) by a self-developed quasi-curved heating method.

Hysteresis Reduction for Organic Thin Film Transistors with Multiple Stacked Functional Zirconia Polymeric Films

We show that transfer hysteresis for a pentacene thin film transistor (TFT) with a low-temperature solution-processed zirconia (ZrOx) gate insulator can be remarkably reduced by modifying the ZrOx surface with a thin layer of crosslinked poly(4-vinylphenol) (c-PVP). Pentacene TFTs with bare ZrOx and c-PVP stacked ZrOx gate insulators were fabricated, and their hysteresis behaviors compared. The different gate insulators exhibited no significant surface morphology or capacitance differences. The threshold voltage shift magnitude decreased by approximately 71% for the TFT with the c-PVP stacked ZrOx gate insulator compared with the bare ZrOx gate insulator, with 0.75 ± 0.05 and 0.22 ± 0.03 V threshold voltage shifts for the bare ZrOx and c-PVP stacked ZrOx gate insulators, respectively. The hysteresis reduction was attributed to effectively covering hysteresis-inducing charge trapping sites on ZrOx surfaces.

Independent driving method for significant hysteresis reduction of piezoelectric stack actuators.

Piezoelectric actuators are used extensively in precision positioning platforms. However, the positioning accuracy is severely affected by the hysteresis characteristics of piezoelectric ceramics. Piezoelectric stack actuators (PSAs) are usually composed of hundreds of thin piezoelectric ceramic layers connected in parallel, and their hysteresis quantity is the accumulation of that in each layer, which results in large nonlinear deformation. A new driving method is proposed for PSAs to drive each layer independently, and all the layers are driven in sequence. The independent driving logic is analyzed, and the scheme of the driving circuit is presented to replace the traditional voltage amplifier, which guarantees that there is no need to change the original driving signal. Experimental results show that the hysteresis of a homemade seven-layer PSA is reduced from approximately 12.5% to 2.7% compared with the traditional parallel driving method in various frequencies. The proposed independent driving method can reduce hysteresis significantly and achieve good linearity in an open-loop control, which does not need high-performance sensors or hysteresis models.

Solution-processed and evaporated C60 interlayers for improved charge transport in perovskite photovoltaics

Abstract Interlayers can strongly influence the interfaces of perovskite solar cells (PSCs), and significantly increase the cells’ stabilized power conversion efficiencies (PCEs). This study compares for the first time the fabrication of C60 interlayers, deposited either by solution-processing or vacuum-based thermal evaporation, at the interface between a SnO2 electron transport layer (ETL) and the perovskite (MAPbI3-xClx) absorber layer in a n-i-p architecture. We evaluate the influence of the C60 deposition method on the perovskite crystallization dynamics and relate it to the device performance. With an optimized C60 layer, the devices exhibit an improvement in the stabilized PCE along with reduced hysteresis. As a result, we achieve improvement from 12.5% to 17.3% on the stabilized PCE of the PSCs. Furthermore, we investigate the influence of the C60 layer thickness on the transport dynamics through time-resolved photoluminescence and transient absorption measurements. Finally, we demonstrate that the C60 interlayers stabilize the constant power output of the solar cells over time due to the reduction in charge carrier accumulation at the ETL/Perovskite interface. Our results indicate that the ETL/perovskite interface is a governing factor in the reduction of hysteresis and in the extension of the stability in the PSCs.

Tuning crystallographic compatibility to enhance shape memory in ceramics

The extraordinary ability of shape-memory alloys to recover after large imposed deformation motivates efforts to transpose these properties onto ceramics, which would enable practical shape-memory properties at high temperatures and in harsh environments. The theory of mechanical compatibility was utilized to predict promising ceramic candidates in the system (Y_(0.5)Ta_(0.5)O_2)_(1−x)−(Zr_(0.5)Hf_(0.5)O_2)_x, 0.6< x < 0.85. When these compatibility conditions are met, a reduction in thermal hysteresis by a factor of 2.5, a tripling of deformability, and a 75% enhancement in strain recovery within the shape-memory effect was found. These findings reveal that predicting and optimizing the chemical composition of ceramics to attain improved crystallographic compatibility is a powerful tool for enabling and enhancing their deformability that could ultimately lead to a highly reversible oxide ceramic shape-memory material.

Enhanced Interfacial Binding and Electron Extraction Using Boron-Doped TiO2 for Highly Efficient Hysteresis-Free Perovskite Solar Cells.

Perovskite solar cells (PSCs) have witnessed astonishing improvement in power conversion efficiency (PCE), more recently, with advances in long‐term stability and scalable fabrication. However, the presence of an anomalous hysteresis behavior in the current density–voltage characteristic of these devices remains a key obstacle on the road to commercialization. Herein, sol–gel‐processed mesoporous boron‐doped TiO2 (B‐TiO2) is demonstrated as an improved electron transport layer (ETL) for PSCs for the reduction of hysteresis. The incorporation of boron dopant in TiO2 ETL not only reduces the hysteresis behavior but also improves PCE of the perovskite device. The simultaneous improvements are mainly ascribed to the following two reasons. First, the substitution of under‐coordinated titanium atom by boron species effectively passivates oxygen vacancy defects in the TiO2 ETL, leading to increased electron mobility and conductivity, thereby greatly facilitating electron transport. Second, the boron dopant upshifts the conduction band edge of TiO2, resulting in more efficient electron extraction with suppressed charge recombination. Consequently, a methylammonium lead iodide (MAPbI3) photovoltaic device based on B‐TiO2 ETL achieves a higher efficiency of 20.51% than the 19.06% of the pure TiO2 ETL based device, and the hysteresis is reduced from 0.13% to 0.01% with the B‐TiO2 based device showing negligible hysteresis behavior.

Titanium-carbide MXenes for work function and interface engineering in perovskite solar cells.

To improve the efficiency of perovskite solar cells, careful device design and tailored interface engineering are needed to enhance optoelectronic properties and the charge extraction process at the selective electrodes. Here, we use two-dimensional transition metal carbides (MXene Ti3C2Tx) with various termination groups (Tx) to tune the work function (WF) of the perovskite absorber and the TiO2 electron transport layer (ETL), and to engineer the perovskite/ETL interface. Ultraviolet photoemission spectroscopy measurements and density functional theory calculations show that the addition of Ti3C2Tx to halide perovskite and TiO2 layers permits the tuning of the materials' WFs without affecting other electronic properties. Moreover, the dipole induced by the Ti3C2Tx at the perovskite/ETL interface can be used to change the band alignment between these layers. The combined action of WF tuning and interface engineering can lead to substantial performance improvements in MXene-modified perovskite solar cells, as shown by the 26% increase of power conversion efficiency and hysteresis reduction with respect to reference cells without MXene.

One-Step Synthesis of TiO2/Graphene Nanocomposites by Laser Pyrolysis with Well-Controlled Properties and Application in Perovskite Solar Cells.

This work presents an original synthesis of TiO2/graphene nanocomposites using laser pyrolysis for the demonstration of efficient and improved perovskite solar cells. This is a one-step and continuous process known for nanoparticle production, and it enables here the elaboration of TiO2 nanoparticles with controlled properties (stoichiometry, morphology, and crystallinity) directly grown on graphene materials. Using this process, a high quality of the TiO2/graphene interface is achieved, leading to an intimate electronic contact between the two materials. This effect is exploited for the photovoltaic application, where TiO2/graphene is used as an electron-extracting layer in n–i–p mesoscopic perovskite solar cells based on the reference CH3NH3PbI3–xClx halide perovskite active layer. A significant and reproducible improvement of power conversion efficiencies under standard illumination is demonstrated, reaching 15.3% in average compared to 13.8% with a pure TiO2 electrode, mainly due to a drastic improvement in fill factor. This beneficial effect of graphene incorporation is revealed through pronounced photoluminescence quenching in the presence of graphene, which indicates better electron injection from the perovskite active layer. Considering that a reduction of device hysteresis is also observed by graphene addition, the laser pyrolysis technique, which is compatible with large-scale industrial developments, is therefore a powerful tool for the production of efficient optoelectronic devices based on a broad range of carbon nano-objects.

Fabrication of V1-xTixO2 thin films by metal-organic decomposition using carbon thermal reduction

V1-xTixO2 thin films were fabricated on Si3N4/SiO2/Si substrates by metal-organic decomposition. The VO2 phase in the range of x = 0–0.25 was obtained by preparing the precursor film calcined at 300 °C for 15 min in a N2 atmosphere and firing these films at 580 °C–600 °C for 15 min in a N2 atmosphere. V1-xTixO2 thin films were successfully obtained by carbon thermal reduction. In the resistance–temperature characteristics, the reduction of hysteresis and the broadening of metal–insulator transition (MIT) occurred with increasing x, and hysteresis and a significant resistance change due to the MIT disappeared at x = 0.25. The temperature coefficients of resistance (TCRs) at x = 0–0.25 were as high as −4.1∼−5.5%/K at 27 °C. At x = 0.25, TCRs were −4.3∼−7.0%/K from 45 °C to 65 °C and a flat temperature dependence of TCR were realized at the temperature range from 10 °C to 80 °C.

Effects of barium substitution on the optical and electrical properties of PLZT transparent electro-optical ceramics

Abstract Transparent electro-optic (EO) ceramics Pb0.91-xLa0.09Bax(Zr0.65Ti0.35)0.9775O3 (PLBZT x/9/65/35) with the amount of x = 0, 0.01, 0.02, 0.04 barium substitution for Pb at A-site were fabricated by hot pressing sintering process. The effects of barium substitution on the micro structure, ferroelectric, dielectric, optical and electro-optic birefringence properties were systematically studied. XRD result shows a typical ABO3 perovskite structure and no second phase observed within the detection limit, which clarifies the entry of Ba2+ ions into PLZT that caused the expansion of the crystal lattice. Due to the mixing ion effect of Pb2+, Ba2+ and La3+ at A-site, both coercive field (Ec) and remnant polarization (Pr) show reducing tendency with increasing doping. And the temperature of the dielectric maximum (Tm) was decreased almost linearly with increasing barium modifying amount. Especially, the reduction of the ferroelectric hysteresis was observed, which may reveal the Ba doping a new method to solve the problems faced now in device designing. In summary, the easily tuned Tm and slim hysteresis loop may prove PLBZT a promising candidate for optical modulator, light switch, energy storage and other relevant applications.

Enhanced n-type β-Ga2O3 (2¯01) gate stack performance using Al2O3/SiO2 bi-layer dielectric

High performance gate stacks are critically needed for the development of β-Ga2O3 power transistors. Significant improvement in the performance of β-Ga2O3 gate stacks is demonstrated in this work by using SiO2 as an interlayer dielectric between Al2O3 and β-Ga2O3. The presence of SiO2 results in an 800× reduction in gate leakage current along with a 1.7× increase in the electric breakdown field. Additionally, the capacitance-voltage characteristics show an increase in flat band voltage (from 0.74 V to 3.25 V) that can enable normally off power transistors. The lowest interface trap density (Dit) of 5.1 × 1010 cm−2 eV−1 for the SiO2/β-Ga2O3 interface has been demonstrated through the use of a piranha clean before SiO2 deposition on β-Ga2O3 for the first time. Reduction (8×) in Dit, hysteresis (from 0.17 V to 0.05 V), and border trap density indicate substantial improvement in the quality of the β-Ga2O3/gate dielectric interface for the Al2O3/SiO2 bilayer stack as compared to only Al2O3.

Reduction of Threshold Voltage Hysteresis of MoS2 Transistors with 3-Aminopropyltriethoxysilane Passivation and Its Application for Improved Synaptic Behavior.

Although molybdenum disulfide (MoS2) is highlighted as a promising channel material, MoS2-based field-effect transistors (FETs) have a large threshold voltage hysteresis (Δ VTH) from interface traps at their gate interfaces. In this work, the Δ VTH of MoS2 FETs is significantly reduced by inserting a 3-aminopropyltriethoxysilane (APTES) passivation layer at the MoS2/SiO2 gate interface owing to passivation of the interface traps. The Δ VTH is reduced from 23 to 10.8 V by inserting the 1%-APTES passivation layers because APTES passivation prevents trapping and detrapping of electrons, which are the major source of the Δ VTH. The reduction in the density of interface traps ( Dit) is confirmed by the improvement of the subthreshold swing (SS) after inserting the APTES layer. Furthermore, the improvement in the synaptic characteristics of the MoS2 FET through the APTES passivation is investigated. Both inhibitory and excitatory postsynaptic currents (PSC) are increased by 33% owing to the reduction in the Δ VTH and the n-type doping effect of the APTES layer; moreover, the linearity of PSC characteristics is significantly improved because the reduction in Δ VTH enables the synaptic operation to be over the threshold region, which is linear. The application of the APTES gate passivation technique to MoS2 FETs is promising for reliable and accurate synaptic applications in neuromorphic computing technology as well as for the next-generation complementary logic applications.

Defect and Contact Passivation for Perovskite Solar Cells.

Metal-halide perovskites are rapidly emerging as an important class of photovoltaic absorbers that may enable high-performance solar cells at affordable cost. Thanks to the appealing optoelectronic properties of these materials, tremendous progress has been reported in the last few years in terms of power conversion efficiencies (PCE) of perovskite solar cells (PSCs), now with record values in excess of 24%. Nevertheless, the crystalline lattice of perovskites often includes defects, such as interstitials, vacancies, and impurities; at the grain boundaries and surfaces, dangling bonds can also be present, which all contribute to nonradiative recombination of photo-carriers. On device level, such recombination undesirably inflates the open-circuit voltage deficit, acting thus as a significant roadblock toward the theoretical efficiency limit of 30%. Herein, the focus is on the origin of the various voltage-limiting mechanisms in PSCs, and possible mitigation strategies are discussed. Contact passivation schemes and the effect of such methods on the reduction of hysteresis are described. Furthermore, several strategies that demonstrate how passivating contacts can increase the stability of PSCs are elucidated. Finally, the remaining key challenges in contact design are prioritized and an outlook on how passivating contacts will contribute to further the progress toward market readiness of high-efficiency PSCs is presented.

Amorphous nanoporous WOx modification for stability enhancement and hysteresis reduction in TiO2-based perovskite solar cells

This work focuses on reducing the hysteresis and improving the stability of TiO2-based perovskite solar cells. A simple slow hydrolysis and rapid evaporation (SHRE) method was developed to deposit amorphous nanoporous WOx up on the TiO2 base at low temperature to form a TiO2-WOx bilayer as composite electron transport materials (ETMs) for efficient CH3NH3PbI3 solar cells. In the composite bilayers, the nanoporous WOx sublayer functions as an effective scaffold to modify the electrical contact between the perovskite and TiO2, and also as an anti-reflective film to enhance light transmittance. The WOx modifying layer much reduces the serious hysteresis and the dependence of power conversion efficiencies (PCEs) on the J–V scan rates. Moreover, it has also significantly enhanced the long-term stability of solar cells. The functioning mechanism for the WOx modifying layer in the TiO2-WOx composite ETMs is explored and interpreted in terms of nanoporous inorganic scaffolds and also the salutary effect of capacitive currents from the high-capacitance WOx.