Activation Energy For Migration Research Articles

Ion Migration and Accumulation in Halide Perovskite Solar Cells†

Comprehensive SummaryThe halide perovskite semiconductors‐based solar cells (PVSCs) show great promise as next‐generation renewable energy sources, with the merits of low cost, high performance, good flexibility, etc. A major difference distinguishing the perovskite semiconductors from others lies in their ionic feature. This intrinsic property induces “freely‐moving” ions to migrate and accumulate in the perovskite films and devices under different external stresses. As a charge carrier, these processes will strongly couple with the electronic process, and dramatically affect the performance and stability of PVSCs. This review summarizes and discusses the recent progresses and fundamental understandings of ion migration and accumulation behaviors in PVSCs. First, the basic principles of the general ion migration are reviewed. Second, following the fundamental understandings, the critical factors, e.g., ion migration activation energy, ion density, ion diffusion coefficient, etc., are extracted to understand the ion migration and accumulation in perovskite film. Third, the principles governing ion accumulation behaviors under different external stresses are discussed. Finally, the effect of ion migration and accumulation on band bending, and device performance is presented. Therefore, we hope this review provides a tutorial and insightful perspective regarding the most prominent ionic feature of perovskite semiconductors and their application for photovoltaics.

An end‐to‐end artificial intelligence platform enables real‐time assessment of superionic conductors

AbstractSuperionic conductors (SCs) exhibiting low ion migration activation energy (Ea) are critical to the performance of electrochemical energy storage devices such as solid‐state batteries and fuel cells. However, it is challenging to obtain Ea experimentally and theoretically, and the artificial intelligence (AI) method is expected to bring a breakthrough in predicting Ea. Here, we proposed an AI platform (named AI‐IMAE) to predict the Ea of cation and anion conductors, including Li+, Na+, Ag+, Al3+, Mg2+, Zn2+, Cu(2)+, F−, and O2−, which is ~105 times faster than traditional methods. The proposed AI‐IMAE is based on crystal graph neural network models and achieves a holistic average absolute error of 0.19 eV, a median absolute error of 0.09 eV, and a Pearson coefficient of 0.92. Using AI‐IMAE, we rapidly discovered 316 promising SCs as solid‐state electrolytes and 129 SCs as cathode materials from 144,595 inorganic compounds. AI‐IMAE is expected to completely solve the challenge of time‐consuming Ea prediction and blaze a new trail for large‐scale studies of SCs with excellent performance. As more experimental and high‐precision theoretical data become available, AI‐IMAE can train custom models and transfer the existing models to new models through transfer learning to constantly meet more demands.

Effect of Ti/Zr doping on the adsorption, dissociation and diffusion of hydrogen on VFe (1 1 0) surface

V-Fe-based alloy is a kind of alternative hydrogen storage material, and Ti or Zr doping is expected to improve hydrogen storage performance of VFe alloy. In this study, based on density functional theory (DFT) calculations, the microscopic characteristics of the hydrogen adsorption behavior on the VFe(110) surface were investigated, and the effect of Ti/Zr doped VFe(110) surface on the hydrogen adsorption behavior was discussed. The results show that the dissociation of H2 on the pure VFe(110) surface only need to overcome small energy barriers (0.556 eV). Moreover, the H2 could be dissociated spontaneously at some active sites due to the interaction with the substrate surfaces. The migration activation energy of H on VFe surface is also small (0.270 eV), while the activation energy required to enter the bulk is large (1.476 eV). After Ti/Zr doping, the dissociation activation energy of hydrogen decreases. Ti/Zr doping can improve the adsorption stability of H atom. Unfortunately, this does not improve the hydrogen storage performance of VFe alloy due to the H atom diffusion on the surface and into bulk are prevented with higher reaction energetic barriers by doping Ti/Zr.

Bright and spectrally stable pure-red CsPb(Br/I)3 quantum dot LEDs realized by synchronous device structure and ligand engineering

All-inorganic CsPbBrxI3−x perovskite quantum dots (PQDs) show great potential for pure-red light-emitting diodes (LEDs). However, spectral instability caused by ion migration at high electric fields and lower luminance limit its practical applications. Here, the ITO/ZnO/PEI/CsPbBrxI3−x PQDs/N, N, N-tris (4-(9-carbazolyl) phenyl) amine (TCTA) (3 nm)/1-bis [4-[N, N-di(4-tolyl)amino]-phenyl]-cyclohexane (TAPC)/MoO3/Au device structure is first designed to reduce the overall operating voltage of the device by enhancing hole injection and transport, effectively avoiding ion migration under high electric fields, and then by post-treating CsPbBrxI3−x PQDs with n-octylphosphonic acid: K to remove surface defects and increase the activation energy of halogen migration, further suppressing ion migration while improving the optical properties of the material. Ultimately, the color-stable pure-red perovskite LED achieved a high luminance of 13730 cd m−2 at voltages as low as 4.9 V and a maximum EQE of 16.7%.

Improved oxygen reduction reaction response of novel spinel structured LaFe2O4 and its heterostructure with Gd-doped-ceria-oxide by Ni foam support for PCFCs cathode

Low-temperature operation of ceramic fuel cells (LT-CFCs; 350° to 550 °C) holds grand promise for abundant large and small scaled applications; if suitable, oxygen reduction electrocatalysts can be developed to hinder sluggish redox reaction at low operating temperature. Herein, we have developed a novel spinal structured cobalt-free LaFe2O4-Gd-doped-CeO2 (LFO-GDC) heterostructure composite as an efficient electrocatalyst for solid oxide fuel cells. The designed LaFe2O4-GDC heterostructure composite exhibits low-area-specific resistance and high oxygen reduction reaction (ORR) activity at low operating temperatures. We have demonstrated high-power densities of 835 mW-cm-2 and a current density of 2216 mA-cm2 at 550 °C for button-sized SOFC with H2 and atmospheric air fuels, and even possible operation at 400 °C. Moreover, the LaFe2O4-GDC heterostructure composite shows minimal proton migration energy and activation energy compared to individual LaFe2O4 and GDC, which help promote ORR activity. Various transmission and spectroscopic measurements such as X-ray diffraction and photoelectron spectroscopy, U-visible, Raman, and density functional theory (DFT) calculations were employed to understand the improved ORR electrocatalytic activity of LaFe2O4-GDC heterostructure composite. The results can further help to develop functional cobalt-free electro-catalysts for LT-SOFCs.

Influence of Fly Ash on the Fluidity of Blast Furnace Slag for the Preparation of Slag Wool

Using fly ash as the modifier, blast furnace slag was modified to prepare slag wool, fulfilling the goal of using one type of waste to make use of another type of waste, and it is of great significance for the comprehensive utilization of industrial bulk solid wastes and resource recycling. In the process of forming fiber from blast furnace slag, fluidity is the key factor affecting the smooth formation of fiber from slag. To explore the changes in the fluidity of modified blast furnace slag, the temperature-dependent viscosity of modified blast furnace slag with different amounts of fly ash added was measured, and the effects of fly ash addition on the viscosity, fluidity, and activation energy of particle migration, and slag structure of modified blast furnace slag were investigated. The results indicated that with the increase in the amount of fly ash added, in the high-temperature region (>1324 °C), the viscosity of modified blast furnace slag increases gradually, the fluidity decreases gradually (i.e., the fluidity becomes worse), and the suitable fiber-forming temperature range gradually widens. When the fly ash addition increases from 5% to 25%, the trend of the activation energy of slag particle migration is as follows: increase, decrease, increase significantly, decrease. When the addition of fly ash is less than 20%, the SiO2 content and slag temperature jointly affect the breakage and reorganization of oxygen bridge bonding in the silicon-oxygen tetrahedron in the slag structure. When the addition of fly ash increases to 25%, the slag temperature dominates the breakage of oxygen bridge bonding in the silicon-oxygen tetrahedron in the slag structure. When using fly ash as the modifier to prepare slag wool, from the perspective of slag fluidity and process operability, the optimum addition amount of fly ash is 15%.

Suppressing the Ion Migration in Halide Perovskite Wafers for Current-Drift Free X-ray Detectors

Metal halide perovskites have been demonstrated as potential X-ray detection materials due to their high defect tolerance, large diffusion length, and high attenuation efficiency. X-ray detectors based on hot-pressed perovskite wafers are investigated intensively recently because of the convenience of scalable fabrication. However, in spite of the large crystal size within wafers, the prepared detectors usually suffer from severe ion migration and current drift under both dark and bright states. In this work, ethylenediamine dihydroiodate (EDDI) was introduced as a strong surface passivation agent, which compensated for the surface iodide vacancy successfully. The ion migration in optimal MAPbI3@EDDI wafer is significantly suppressed, which is manifested by increased migration activation energy and stable current under high bias for 10 h. Moreover, the introduction of EDDI also reduced the dark current, contributing a high on–off ratio and a champion sensitivity of 8291.22 μC Gyair–1 cm–2. A low detection limit of 340 nGyair s–1 is also obtained, which is much lower than that of commercial X-ray detectors. Besides, the as-fabricated X-ray detector can endure long-term operation with flat current under a high bias of 20 V. This work provides a route for the performance improvement of perovskite wafer-based X-ray detectors.

Li ion diffusion behavior of Li3OCl solid-state electrolytes with different defect structures: insights from the deep potential model.

Li3OX (X = Cl, Br), a lithium-rich anti-perovskite material developed in recent years, has received tremendous attention due to its high ionic conductivity of >10-3 S cm-1 at room temperature. However, the origin of the high ionic conductivity of the material at the atomic level is still not clear. In this work, we investigated the dynamic behavior of the Li3OCl system with three different defect structures (Li-Frenkel, LiCl-Schottky, and Cl-O anti-site disorder) at seven temperature intervals and calculated its ionic conductivity using the deep potential (DP) model. The results show that the presence of LiCl-Schottky defects is the main reason for the high performance of the Li3OCl system, and the Li vacancy is the main carrier. The ionic conductivity obtained from the DP model is 0.49 × 10-3 S cm-1 at room temperature and it can reach 10-2 S cm-1 above the melting point, which is in the same order of magnitude as the experimentally reported results. We also explored the effect of different defect concentrations on the ionic conductivity and migration activation energy. This work also demonstrates the feasibility of the DP method for solving the accuracy-efficiency dilemma of ab initio molecular dynamics (AIMD) and classical molecular dynamics simulations.

Density Functional Theory Search of 3d Transition Metal Complexes in Diamond for Quantum Sensing Applications

Optically addressable defects in wide‐bandgap semiconductors are of considerable interest as materials platforms for quantum sensing and information systems. Density functional theory is used to identify novel defects in diamond consisting of transition metal + nitrogen complexes with potential for quantum sensing. Defects are characterized with respect to formation energy, ordering and degeneracy of the defect energy levels, optical and charge transition energies, zero‐field‐splitting energies, and thermodynamic stability. Novel defect sites with optically addressable spin states and viable spin sublevel configurations are identified, and analysis of activation energies for atomic migration indicates stability in the lattice.

First-principles study of the microstructure evolution of the diamond (110) surface with the adsorption of Fe atoms

Understanding the diamond graphitization mechanism is an essential subject in manufacturing research since it helps elucidate the reason for the material removal. Our work addressed the mechanism of Fe-induced graphitization of diamond (110) surfaces (Dia-(110)-Surf) by first-principles calculations. The results pointed out that Fe atoms adsorbed at hollow sites could acquire the most stable configuration on the Dia-(110)-Surf. Meanwhile, the Fe adatom could change interlayer binding energies of CC bonds of various layered. As the amount of Fe atoms increased, the weakening/enhancement effect of CC bonds tended to be apparent. Interestingly, Fe adatoms not only changed interlayer binding energies of CC nearby but also affected the dissociation direction of the surface microstructure. The weakened CC bonds could provoke the flattening of the sixfold chair ring structure of C atoms. The extension direction of the sixfold chair ring structure changed from horizontal to oblique, resulting in eliminating lateral compressive stress. It might be the origin of the Fe-induced graphitization of Dia-(110)- Surf. Moreover, the migration behaviors of the Fe atom have been studied. It could be inferred that the migration activation energy and movement direction of Fe adatoms were associated with the material removal rate.

Negligible Ion Migration in Tin‐Based and Tin‐Doped Perovskites

AbstractIon migration is a notorious phenomenon observed in ionic perovskite materials. It causes several severe issues in perovskite optoelectronic devices such as instability, current hysteresis, and phase segregation. Here, we report that, in contrast to lead halide perovskites (LHPs), no ion migration or phase segregation was observed in tin halide perovskites (THPs) under illumination or an electric field. The origin is attributed to a much stronger Sn‐halide bond and higher ion migration activation energy (Ea) in THPs, which remain nearly constant under illumination. We further figured out the threshold Ea for the absence of ion migration to be around 0.65 eV using the CsSnyPb1‐y(I0.6Br0.4)3 system whose Ea varies with Sn ratios. Our work shows that ion migration does not necessarily exist in all perovskites and suggests metallic doping to be a promising way of stopping ion migration and improving the intrinsic stability of perovskites.

Negligible Ion Migration in Tin-Based and Tin-Doped Perovskites.

Ion migration is a notorious phenomenon observed in ionic perovskite materials. It causes several severe issues in perovskite optoelectronic devices such as instability, current hysteresis, and phase segregation. Here, we report that, in contrast to lead halide perovskites (LHPs), no ion migration or phase segregation was observed in tin halide perovskites (THPs) under illumination or an electric field. The origin is attributed to a much stronger Sn-halide bond and higher ion migration activation energy (Ea ) in THPs, which remain nearly constant under illumination. We further figured out the threshold Ea for the absence of ion migration to be around 0.65 eV using the CsSny Pb1-y (I0.6 Br0.4 )3 system whose Ea varies with Sn ratios. Our work shows that ion migration does not necessarily exist in all perovskites and suggests metallic doping to be a promising way of stopping ion migration and improving the intrinsic stability of perovskites.

Caution! Static Supercell Calculations of Defect Migration in Higher Symmetry ABX3 Perovskite Halides May Be Unreliable: A Case Study of Methylammonium Lead Iodide.

Activation energies of defect migration in ABX3 perovskite halides are widely obtained through static supercell calculations with the nudged-elastic-band method. Taking methylammonium lead iodide (CH3NH3PbI3, MAPbI3) as an example, we demonstrate that such calculations are unreliable for the higher symmetry structures adopted by the material at temperatures relevant to device operation (tetragonal and cubic MAPbI3) because, in addition to ion relaxation around the point defects, local structural modifications characteristic of the ground-state (orthorhombic) structure occur. In this way, we offer a simple explanation of why calculated activation energies of defect migration in MAPbI3 suffer from surprisingly large scatter. We propose a robust test to determine whether static supercell calculations of point-defect processes in ABX3 perovskite systems are reliable.

A full-scale Monte Carlo Potts model and real time conversion under non-uniform temperature distribution

Prediction of microstructure evolution is important to design structural materials, and grain growth is the most fundamental but important one which determines mechanical properties. The Monte Carlo Potts is a widespread simulation model for grain growth with high computational efficiency but has not been considered suitable for the quantitative prediction of practical processes since the physical meaning of variables is not fully understood yet. Efforts have been made to assign realistic physical meaning to variables. The existing equation for converting simulation time to real time involves a strong temperature dependence, which causes a problem under non-uniform temperature distribution, as in additive manufacturing. This problem could be solved by assigning a temperature dependence to the simulation result, which was possible by using realistic temperature and energy values. We found that the simulated activation energy for grain growth could be equated to the experimental value by adjusting the activation energy for grain boundary migration within a reasonable range in the simulation. The modified model made the time conversion equation completely temperature-independent and was free from the above-mentioned problem in time conversion. The Monte Carlo Potts simulation can now more reasonably predict grain growth in various materials under various temperature conditions.

Effects of Zr addtion on recrystallization behaviors and mechanical properties of FeCrAl alloys

The effects of Zr addition on the microstructural evolution and mechanical properties of FeCrAl alloys were investigated. Fine Fe2Zr particles with their sizes ranging from 0.5 to 1.2 μm were observed when the alloying element Zr was introduced in FeCrAl alloy. The addition of Zr led to the formation of Fe2Zr particles either within the grains or on the grain boundaries, and this was found to enhance the strength of the FeCrAl alloys. Moreover, the Fe2Zr particles stabilized the microstructures by promoting recrystallization nucleation and retarding grain growth. The critical size of the Fe2Zr particles for stimulating recrystallization nucleation and the activation energy of grain boundary migration during recrystallization were determined. The effects of Fe2Zr particles on particle-stimulated nucleation behavior and recrystallization grain growth dynamics are discussed.

Improving the sensitivity of LaMnO3 NTC films by Al ion implantation

The Al ion implantation was employed to modify the NTC characteristics of LaMnO3 thin films sputtered on Si/SiO2 substrates under different annealing temperatures. The crystal structure, morphology and ion distribution of the as-sputtered LaMnO3 thin films and as-annealed Al-implanted films were carefully evaluated. Results indicated that (LaMnAlxO3)y(Al2O3)1-y composite phase existed over the annealing temperature range after Al3+ implanting into the LaMnO3 film of perovskite phase. The film was nucleated throughout and the size of the grain decreased with the increase in annealing temperature. The Al3+ implantation promoted the reduction of oxygen vacancy concentration while leading to the reduction in the equilibrium oxygen vacancy. As a result, the Mn3+/Mn4+ ratio declined and the number of carriers reduced, which helped to increase the carrier migration barrier and activation energy. The direct manifestation of the latter is the increase of the thermal constant B value from 3192 K to 2111 K based on the premise of resistivity is closed. The successful modification of a traditional perovskite-type NTC material will bring an innovative perspective to the design of advanced functional film materials and provide ideas for further exploration of the material in high B and low resistivity temperature sensor applications.

Asymmetric Diammonium Directed In-Plane Charge Transport Enhancement in Two-Dimensional Lead Bromide Perovskite for Weak-Light Detection.

Two-dimensional (2D) Dion-Jacobson (DJ) perovskites are drawing significant attention in optoelectronic fields because of their enhanced out-of-plane electron coupling and improved structure stability. However, the structural effects of organic cations on the in-plane charge transport properties of 2D DJ lead bromide perovskites have remained less explored. Herein, we adopt asymmetric 3-(dimethylamino)-1-propylammonium (DMPD) and symmetric butane-1,4-diammonium (BDA) to systematically investigate the influence of organic cations on the structural, optical, and in-plane charge transport properties of 2D lead bromide perovskites. The large penetration depth of DMPD2+ induces a decreased perovskite layer distortion and a lower bandgap in DMPDPbBr4, compared with that of BDAPbBr4. Moreover, DMPDPbBr4 is shown to possess a low exciton binding energy, a low defect density, and a low ion migration activation energy, thereby yielding a more efficient in-plane charge collection efficiency than BDAPbBr4. Density functional theory calculations suggest that the improved in-plane charge transport can be traced to the enlarged antibonding coupling between Pb-6s and Br-4p orbitals that enables a high band dispersion and a low carrier effective mass in the in-plane direction of DMPDPbBr4. Finally, the planar Ag/DMPDPbBr4/Ag photodetector delivers a satisfying detectivity of 1.73 × 1012 Jones under an incident power intensity of 0.16 mW cm-2 and a high on/off ratio of 5.3 × 103. The above findings offer novel insight for the design of 2D DJ lead bromide perovskites for optoelectronic devices.

Rapid discovery of inorganic-organic solid composite electrolytes by unsupervised learning

Inorganic-organic solid composite electrolytes (SCEs) have been widely concerned owing to their excellent film forming performance, good wettability and low flammability. However, their high polymer crystallinity leads to the low ionic conductivity (σ), seriously impeding practical applications. Discovering SCEs with high σ through trial-and-error experiments and high-throughput calculations from massive material search space is an impractical task. The severe scarcity of experimental data on known SCEs even limits the utilization of supervised learning. Here, we adopted an unsupervised learning (UL) model to discover new SCEs with high σ based on <50 known experimental data. Our model revealed the key physical factors that affected the σ and clustered most of the known SCEs with high σ into four groups. From that we rapidly identified 49 promising SCEs with high σ, compared them with previous experimental results, and found two structures with the lowest Li+ migration activation energy (only 0.212 eV). This work fully exploited the potential of UL to overcome the limitations of data scarcity in material discovery. Importantly, we shortened the screening period of SCEs by ∼23 years, providing a new idea for the rapid discovery and targeted design of materials for solid-state batteries.

Critical ionic transport across an oxygen-vacancy ordering transition

Phase transition points can be used to critically reduce the ionic migration activation energy, which is important for realizing high-performance electrolytes at low temperatures. Here, we demonstrate a route toward low-temperature thermionic conduction in solids, by exploiting the critically lowered activation energy associated with oxygen transport in Ca-substituted bismuth ferrite (Bi1-xCaxFeO3-δ) films. Our demonstration relies on the finding that a compositional phase transition occurs by varying Ca doping ratio across xCa ≃ 0.45 between two structural phases with oxygen-vacancy channel ordering along <100> or <110> crystal axis, respectively. Regardless of the atomic-scale irregularity in defect distribution at the doping ratio, the activation energy is largely suppressed to 0.43 eV, compared with ~0.9 eV measured in otherwise rigid phases. From first-principles calculations, we propose that the effective short-range attraction between two positively charged oxygen vacancies sharing lattice deformation not only forms the defect orders but also suppresses the activation energy through concerted hopping.

Studies of recrystallization in rhenium using positron annihilation spectroscopy

Pure rhenium exposed to cold-rolling was subjected to annealing studies using positron annihilation techniques. The recovery and recrystallization processes were observed using these techniques and they were confirmed by hardness measurement and X-ray diffraction. Using the positron diffusion trapping model the activation energy of the grain boundary migration was determined as 1.08±0.05 eV, and the recrystallization temperature was estimated to be around 950 °C. Additionally, the bulk positron lifetime in this metal determined as 98.38±0.30 ps.