Material Design Guidelines Research Articles

Recent advances in non-fullerene organic solar cells: from lab to fab.

Recently, the laboratory-scale power conversion efficiency (PCE) of organic solar cells (OSCs) has reached 18% in single-junction devices due to a combination of the rapid development of novel light-harvesting/interfacial materials and device engineering. Thus, such materials show considerable application prospects in the near future. It is of great importance to develop economically achievable, highly efficient, thickness-tolerant photovoltaic materials and processing methods for the manufacture of large flexible solar panels. Research in this area has been conducted from the very early stages of the development of organic photovoltaic materials and has never stopped. Herein, we focus on the fundamental requirements of photoactive materials and the processing methods used for commercialization based on the recent advances of the booming PCEs, to provide guidelines for future material design and mass production. In this review, the progress toward high-performance materials is briefly summarized, and the essential requirements for large-area printing modules, such as thickness tolerance and cost issues, and the latest findings on non-fullerene OSCs are introduced. In particular, important advances in the material design and device optimization of thick-film OSCs have been discussed. Significant advances in the processing methods used to prepare efficient non-fullerene OSCs and the challenges for the industrialization of OSCs are presented. Furthermore, the prospects and opportunities in this emerging field of research are also discussed.

Frustrated and Allowed Structural Transitions: The Theory-Guided Discovery of the Modulated Structure of IrSi.

To the experienced molecular chemist, predicting the geometries and reactivities of a system is an exercise in balancing simple concepts such as sterics and electronics. In this Article, we illustrate how recent theoretical developments can give this combination of concepts a similar predictive power in intermetallic chemistry through the anticipation and discovery of structural complexity in the nominally MnP-type compound IrSi. Analysis of the bonding scheme and DFT-Chemical Pressure (CP) distribution of the reported MnP-type structure exposes issues pointing toward new structural behavior. The placement of the Fermi energy below an electronic pseudogap indicates that this structure is electron-poor, an observation that can be traced via the 18-n rule to the structure's Ir-Ir connectivity. In parallel with this, the structure's CP scheme highlights facile paths of atomic motion that could enable a structural response to this electronic deficiency. Combined, these analyses suggest that IrSi may adopt a more complex structure than previously recognized. Through synthesis and detailed structural investigation of this phase, we confirm this prediction: single-crystal X-ray diffraction reveals an incommensurately modulated structure with the (3+1)D superspace group P21/n(0βγ)00 and q ≈ -0.22b* + 0.29c*. The structural modulations increase the average number of Ir-Ir bonds to nearly match the 18-n expectations of the phase through Ir-Ir trimerization along negative CPs with the incommensurability arising from the difficulty of contracting and stretching the Ir-Ir contacts in a regular pattern without expanding the structure along directions of negative Si-Si CP. Integrating these results with prior analyses of related systems points to a simple guideline for materials design, the Frustrated and Allowed Structural Transitions (FAST) principle: the ease with which competing structural phenomena can be experimentally realized is governed by the degree to which they are supported by the coordination of the atomic packing and electronic factors.

The electronic transport characteristics in wide band-gap nitrogen vacancy diamond/Si hetero-structure using Raman spectrum

Abstract The negative charged nitrogen vacancy center in diamond is ideal sensitive detectors for quantum measure applications. Raman active phonon and inelastic light scattering in face-centered cubic diamond/Si(1 0 0) films were primarily studies by Raman spectra in various scattering configurations and NV concentration. The fabricated diamond (1 0 0) thin films were successfully epitaxial grown on Si(1 0 0) substrate using MPCVD. The Raman scattering spectrum of diamond/Si(1 0 0) hetero-structure with different thickness nanostructure is present to investigate spin orbital transport dynamics of phase transition. Diamond hetero-junction experiments were carried out at different conditions such as temperature range of 15–300 K and concentration of NV. The results show a strong peak at 1332 cm−1 of D mode indicates the E2g of diamond, as well as the peak 1550 cm−1 of a broad band F2g symmetry G mode which corresponds to the nano-diamond. The disordered graphitic carbon is formed by disordered SP2 hybridization. The 1132 cm−1 and 1480 cm−1 are corresponding with hydrogen bonding within film grain boundaries. The transfer of diamond sp2 content extracted from C C peak and converted to the sp3 spin related effect. The diamond/Si(1 0 0) PDOS indicated the spin-related couple of SP3, and p and d orbital hybridization. The research leads to a better understanding of the Raman active spectra and inelastic light scattering of diamond/Si(1 0 0) films and offers guidelines for better orbital hybridization material design in deep ultra-violet photo-sensor, gyroscopes, field effect transistors (FET) using diamond hetero-structure and high-k oxide gate structure, magnetometer, thermometer, and optical switching micro-electromechanical system (MEMS) devices.

Enhanced π-π Interactions of Nonfullerene Acceptors by Volatilizable Solid Additives in Efficient Polymer Solar Cells.

Fine-tuning of the nanoscale morphologies of the active layers in polymer solar cells (PSCs) through various techniques plays a vital role in improving the photovoltaic performance. However, for emerging nonfullerene (NF) PSCs, the morphology optimization of the active-layer films empirically follows the methods originally developed in fullerene-based blends and lacks systematic studies. In this work, two solid additives with different volatilities, SA-4 and SA-7, are applied to investigate their influence on the morphologies and photovoltaic performances of NF-PSCs. Although both solid additives effectively promote the molecular packing of the NF acceptors, due to the higher volatility of SA-4, the devices processed with SA-4 exhibit a power conversion efficiency of 13.5%, higher than that of the control devices, and the devices processed with SA-7 exhibit poor performances. Through a series of detailed morphological analyses, it is found that the volatilization of SA-4 after thermal annealing is beneficial for the self-assembly packing of acceptors, while the residuals due to the incomplete volatilization of SA-7 have a negative effect on the film morphology. The results delineate the feasibility of applying volatilizable solid additives and provide deeper insights into the working mechanism, establishing guidelines for further material design of solid additives.

Developing a predictive model for nanoimprint lithography using artificial neural networks

Nanoimprint lithography (NIL) is a high-throughput and cost-effective technique for fabricating nanoscale features. However, the fine tuning of NIL process parameters is critical in achieving defect-free imprints. Currently, there exists no unified material and process design guidelines to deal with the complex set of process parameters. In this research, an artificial neural network (ANN) algorithm was developed to predict the imprint quality based on a set of input factors collected from experiments and literature. The prediction accuracy was tested in two stages by the use of three ANN models - General Regression Neural Network (GRNN), Back Propagation Neural Network (BPNN), and Probabilistic Neural Network (PNN). Higher prediction accuracy was observed for GRNN in both stages (1st stage=58.22% and 2nd stage=92.37%). A significant increase in the prediction accuracy was observed in the second stage after including additional input factors and larger data set. The average prediction accuracies for GRNN, BPNN, and PNN in the second stage were reported as 92.37%, 84.79%, and 91.19%, respectively. The prediction of the GRNN model was validated with experimental results confirming the accurate classification of all the outputs. This research lays the foundation for the development of an expert system for nanoimprint lithography.

The Status of Existing Building Materials in Thailand to Cope with Future Climate: Wall Component

Climate change tolerant building materials, such as high temperature resistance and flooding resistance, affect living condition of people in an accommodation. This study focuses on durability features of building material related with climate change in Thailand. The result suggests that the property of each wall material type cannot show proper value of tolerance and climate change resistance. Therefore, the conclusion for future tolerant building material properties are that the U-value should be greater than 0.64 W/m2k, the R-Value should be greater than 0.64 m2k/W, and the K-Value should be less than 0.155 W/m°C. Such values can cope with temperature up to approximately 49 degree Celsius. Apart from that, flood resistance should be less than or equal to 2%, water penetration should be less than or equal to 1.5% and swelling test should be less than or equal to 12%. This will be able to cope with flood that lasts about 60 days. The results of the study is a guideline for future wall material design and development.

Interlayer-Spacing-Regulated VOPO4 Nanosheets with Fast Kinetics for High-Capacity and Durable Rechargeable Magnesium Batteries.

Owing to the low-cost, safety, dendrite-free formation, and two-electron redox properties of magnesium (Mg), rechargeable Mg batteries are considered as promising next-generation secondary batteries with high specific capacity and energy density. However, the clumsy Mg2+ with high polarity inclines to sluggish Mg insertion/deinsertion, leading to inadequate reversible capacity and rate performance. Herein, 2D VOPO4 nanosheets with expanded interlayer spacing (1.42 nm) are prepared and applied in rechargeable magnesium batteries for the first time. The interlayer expansion provides enough diffusion space for fast kinetics of MgCl+ ion flux with low polarization. Benefiting from the structural configuration, the Mg battery exhibits a remarkable reversible capacity of 310 mAh g-1 at 50 mA g-1 , excellent rate capability, and good cycling stability (192 mAh g-1 at 100 mA g-1 even after 500 cycles). In addition, density functional theory (DFT) computations are conducted to understand the electrode behavior with decreased MgCl+ migration energy barrier compared with Mg2+ . This approach, based on the regulation of interlayer distance to control cation insertion, represents a promising guideline for electrode material design on the development of advanced secondary multivalent-ion batteries.

Droplet Cloaking Imaging and Characterization

Lubricant infused surfaces (LIS or SLIPS) have potential to enhance a variety of applications due to their non-wetting characteristics. Recently, LIS and SLIPS have been shown to greatly improve dropwise condensation heat transfer performance by enabling ultra-low contact angle hysteresis (< 5°) and droplet-surface adhesion. The low adhesion characteristics arise from the ultra-smooth liquid-liquid interface that depends on the lubricating fluid remaining infused into the surface by capillary forces. A key limiting phenomenon of LIS and SLIPS is cloaking, whereby the infused lubricant spreads and forms a very thin layer (∼100 nm) over liquid droplet residing on the substrate. This can lead to degradation due to drainage of the lubricant layer. Cloaking involves several fluid interfaces between the lubricant, droplet and air, and the resolution of the lubricant-droplet interface is essential to cloaking imaging and characterization. Our work involves goniometric measurements of advancing and receding contact angles, imaging of cloaked water droplets on LIS and SLIPS, and the characterization of cloaking during shear induced flow. The LIS and SLIPS substrates were created by spin coating lubricants of various viscosities (5 – 2712 cSt) onto superhydrophobic nanostructured boehmite (AlO(OH)). Cloaking effects were observed by inhibition of water droplet evaporation (Fig. a). Furthermore, the lubricantdroplet interface for non-cloaking droplets was resolved using lubricant-miscible dyes (Fig. a). Cloaking was also characterized by studying shear induced flow of both condensate and artificially injected droplets, resulting in lubricant drainage as shown in Figures (b) and (c). The results of this work not only provide a basis for understanding the lubricant-droplet interactions on LIS and SLIPS, but also material design guidelines for future LIS and SLIPS coatings.

Numerical study of inclusion parameters and their influence on fatigue lifetime

The understanding of the influence of inclusion parameters like size, shape and surface roughness on the material’s fatigue behavior can provide important guidelines for future material design. In this study, a numerical model is used to calculate the influence of inclusions on fatigue properties. The model consists of the statistical evaluation of numerous representative volume element (RVE) calculations in combination with a crystal plasticity (CP) constitutive model. The RVEs contain inclusions which differ in size, shape, surface roughness and elastic mismatch to the matrix. These parameters have been identified to determine the fatigue lifetime for the case that inclusions are the origin of failure. For each inclusion type, up to 100 RVEs are generated. The RVEs have statistically equivalent distributed microstructural properties but differ in detail, though. The results show that the inclusion size has the biggest influence on the lifetime. The influence of shape and roughness of the inclusion surface is negligible small. The study of the elastic mismatch is matching literature findings. All in all, this study shows that the numerical model can be used to calculate the influence of inclusions on fatigue lifetime. The use of the model can help to reduce the experimental effort for specifying the minimum cleanness requirement of a steel to guarantee the structural integrity under cyclic loading.

Highly efficient voltage control of spin and enhanced interfacial perpendicular magnetic anisotropy in iridium-doped Fe/MgO magnetic tunnel junctions

Voltage control of spin enables both a zero standby power and ultralow active power consumption in spintronic devices, such as magnetoresistive random-access memory devices. A practical approach to achieve voltage control is the electrical modulation of the spin–orbit interaction at the interface between 3d-transition-ferromagnetic-metal and dielectric layers in a magnetic tunnel junction (MTJ). However, we need to initiate a new guideline for materials design to improve both the voltage-controlled magnetic anisotropy (VCMA) and perpendicular magnetic anisotropy (PMA). Here we report that atomic-scale doping of iridium in an ultrathin Fe layer is highly effective to improving these properties in Fe/MgO-based MTJs. A large interfacial PMA energy, Ki,0, of up to 3.7 mJ m−2 was obtained, which was 1.8 times greater than that of the pure Fe/MgO interface. Moreover, iridium doping yielded a huge VCMA coefficient (up to 320 fJ Vm−1) as well as high-speed response. First-principles calculations revealed that Ir atoms dispersed within the Fe layer play a considerable role in enhancing Ki,0 and the VCMA coefficient. These results demonstrate the efficacy of heavy-metal doping in ferromagnetic layers as an advanced approach to develop high-density voltage-driven spintronic devices.

A Pore Network Modelling Study of Fuel Cell Gas Diffusion Layers with Patterned Wettability

Further improvements in power density of polymer electrolyte fuel cells (PEFCs) are required to lower the cost. At high current densities, mass transport related resistances limit the performance due to, mainly, a poor water management within the cell. It is therefore paramount to develop advanced water management strategies to maximize power output. In this context, diffusion layers play a notable role. They must ensure efficient gas transport toward the catalyst layer while removing the electrochemically produced liquid water in the opposite flow direction. A substantial amount of work has been carried out to improve gas diffusion layers (GDLs) and microporous layer over the last years, mainly controlling microstructural features, such as pore sizes, fiber arrangements and porosities, and hydrophobic coating load and distribution [1]. Our group has recently developed an approach consisting of artificially creating hydrophilic patterns throughout the entire GDL thickness using the radiation grafting method. The hydrophilic areas act as low pressure liquid water removal pathways, therefore liberating the remaining areas for the gas to flow throughout less tortuous domains [2]. The performance of PEFCs was significantly increased thanks to the use of the modified GDLs [3]. However, there is still plenty of room for improvement. Capillary pressure is the driving force for liquid water transport and it is influenced by the microstructure and liquid-solid interaction [4]. It therefore stands to reason that, for a given application, further optimization can be achieved when selecting the appropriate diffusion layer microstructure and wettability ratio. While the first experimental data investigating the effect of GDL morphology, contact angle and coating load has been recently published, these experiments require notable infrastructure and time efforts [5]. For that reason, modelling capillary pressure experiments using pore network models can be a valid approach to theoretically assess optimal material parameters. The open-source OpenPNM framework, which has been extensively used in recent fuel cell literature [6], was the software of choice for this investigation. In this talk we will start by presenting the model physics in which a modification of the Washburn equation has been used as required in the intermediate wettability range where this model fails to predict accurately water imbibition and the validation strategy. The definition of coating load and contact angle will be discussed. A good agreement was obtained between model and experiments, specially investigating the influence of coating load, contact angle and pore size distributions. In the second part of the talk, we will provide some material design guidelines based on model output information to maximize the quality of water segregation in GDLs with patterned wettability.

Photoactive/Passive Molecular Glass Blends: An Efficient Strategy to Optimize Azomaterials for Surface Relief Grating Inscription.

Irradiation of azomaterials causes various photophysical and photomechanical effects that can be exploited for the preparation of functional materials such as surface relief gratings (SRGs). Herein, we develop and apply an efficient strategy to optimize the SRG inscription process by decoupling, for the first time, the important effects of the azo content and glass transition temperature (Tg). We prepare blends of a photoactive molecular glass functionalized with the azo Disperse Red 1 (gDR1) with a series of analogous photopassive molecular glasses. Blends with 10 and 40 mol % of gDR1 are completely miscible, present very similar optical properties, and cover a wide range of Tg from below to well above ambient temperature. SRG inscription experiments show that the diffraction efficiency (DE), residual DE, and initial inscription rate reach a maximum when Tg is 25-40 °C above ambient temperature for low to high azo content, respectively. Indeed, for a fixed 40 mol % azo content, choosing the optimal Tg enables doubling the SRG inscription rate and increasing DE 6-fold. Moreover, a higher azo content enables higher DE for a similar Tg. Spectroscopy measurements indicate that the photo-orientation of DR1 and its thermal stability are maximal with Tg around 70 °C, independent of the azo content. We conclude that the SRG potential of azomaterials depends on their capability to photo-orient but that the matrix rigidity eventually limits the inscription kinetics, leading to an optimal Tg that depends on the azo content. This study exposes clear material design guidelines to optimize the SRG inscription process and the photoactivity of azomaterials.

Materials Design Guidelines for All-Solid-State Batteries

All-solid-state batteries with non-flammable solid-state electrolytes have significant advantages over Li-ion or Na-ion batteries with liquid electrolytes. In this poster we will present our recent advances in understanding the fundamental relationship between crystal structure and ionic transport in fast Li-ion conductors [1]. We find that the topology of the sites along the lithium hopping path, and the volume per anion, largely control the activation energy for Li motion. This topology is more favorable in compounds where the anions form a bcc lattice than in the typical close-packed fcc and hcp anion arrangements, explaining why most compounds are not fast-ion conductors. Furthermore, an accurate and efficient first-principles computational methodology has been developed to evaluate thermodynamic stability of the solid-state electrolyte against battery electrodes [2]. These findings not only provide valuable insights towards the understanding of materials behaviors in discovered ionic conductors, but also serve as design principles for new Li and Na conducting materials and all-solid-state batteries. We will also report a few novel Li and Na ionic conductors that are predicted based on our design principles and experimentally confirmed by our collaborators. [1] Y. Wang, et al., “Design principles for solid-state lithium superionic conductors,” Nat. Mater., 14, 1026-1031, (2015). [2] W. Richards, et al., “Interface stability in solid-state batteries”, Chem. Mater., 28, 266-273, (2016).

A microstructure-guided constitutive modeling approach for random heterogeneous materials: Application to structural binders

This paper presents a microstructure-guided modeling approach to predict the effective elastic response of heterogeneous materials, and demonstrates its application toward two highly heterogeneous, unconventional structural binders, i.e., iron carbonate and fly ash geopolymer. Microstructural information from synchrotron X-ray tomography (XRT) and intrinsic elastic properties of component solid phases from statistical nanoindentation are used as the primary inputs. The virtual periodic 3D microstructure reconstructed using XRT, along with periodic boundary conditions is used as a basis for strain-controlled numerical simulation scheme in the linear elastic range to predict the elastic modulus as well as the stresses in the microstructural phases. The elastic modulus of the composite material predicted from the microstructure-based constitutive modeling approach correlates very well with experimental measurements for both the materials considered. This technique efficiently links the microstructure to mechanical properties of interest and helps develop material design guidelines for novel heterogeneous composites.

Predictive modeling of interfacial damage in substructured steels: application to martensitic microstructures

Metallic composite phases, like martensite present in conventional steels and new generation high strength steels exhibit microscale, locally lamellar microstructures characterized by alternating layers of phases or crystallographic variants. The layers can be sub-micron down to a few nanometers thick, and they are often characterized by high contrasts in plastic properties. As a consequence, fracture in these lamellar microstructures generally occurs along the layer interfaces or within one of the layers, typically parallel to the interface. This paper presents a computational framework that addresses the lamellar nature of these microstructures, by homogenizing the plastic deformation at the mesoscale by using the microscale response of the laminates. Failure is accounted for by introducing a family of damaging planes that are parallel to the layer interface. Mode I, mode II and mixed-mode opening are incorporated. The planes along which failure occurs are captured using a smeared damage approach. Coupling of damage with isotropic or anisotropic plasticity models, like crystal plasticity, is straightforward. The damaging planes and directions do not need to correspond to crystalline slip planes, and normal opening is also included. Focus is given on rate-dependent formulations of plasticity and damage, i.e. converged results can be obtained without further regularization techniques. The validation of the model using experimental observations in martensite-austenite lamellar microstructures in steels reveals that the model correctly predicts the main features of the onset of failure, e.g. the necking point, the failure initiation region and the failure mode. Finally, based on the qualitative results obtained, some material design guidelines are provided for martensitic and multi-phase steels.

Recent progress of high performance polymer OLED and OPV materials for organic printed electronics

The development of organic printed electronics has been expanding to a variety of applications and is expected to bring innovations to our future life. Along with this trend, high performance organic materials with cost-efficient fabrication processes and specific features such as thin, light weight, bendable, and low power consumption are required. A variety of organic materials have been investigated in the development of this field. The basic guidelines for material design and the recent progress of polymer-based organic light-emitting diodes (OLEDs) and organic photovoltaic cells (OPVs) are reported.

ChemInform Abstract: Materials Design Considerations for Charge Generation in Organic Solar Cells

AbstractReview: 176 refs.

Materials Design Considerations for Charge Generation in Organic Solar Cells

This article reviews some of our recent progress on materials design guidelines for photoinduced charge generation in bulk-heterojunction organic solar cells. Over the last 7 years, our group has employed transient absorption measurement to determine the relative quantum yields of long-lived polaron pairs for over 300 different organic Donor/Acceptor blend films. We have shown that this optical assay of charge separation can be a strong indicator of photocurrent generation efficiency in complete devices. In this review, we consider the lessons that can be drawn from these studies concerning the parameters that determine efficiency of this photoinduced charge separation in such solar cells. We consistently find, from studies of several materials series, that the energy offset driving charge separation is a key determinant of the efficiency of this charge generation, and thereby photocurrent generation. Moreover, we find that the magnitude of the energy offset required to drive charge separation, and the st...

Band inversion mechanism in topological insulators: A guideline for materials design

Alteration of the topological order by band inversion is a key ingredient of a topologically nontrivial material. Using first-principles calculations for HgTe, PtScBi, and Bi${}_{2}$Se${}_{3}$, we argue that it is not accurate to ascribe the band inversion to the spin-orbit coupling. Instead, scalar relativistic effects and/or lattice distortions are found to be essential. Therefore, the search for topologically nontrivial materials should focus on band shifts due to these mechanisms rather than spin-orbit coupling. We propose an effective scheme to search for new topological insulators.

First-Principles Study of Structural Trend of BiMO3 and BaMO3: Relationship between Tetragonal or Rhombohedral Structure and the Tolerance Factors

The relationship between a tetragonal or rhombohedral structure and the tolerance factors in BiMO3 and BaMO3 has been investigated using a first-principles calculation with optimized structures. BiMO3 and BaMO3, which consist of M ions with d0-state transition metals (TMs) or non-TMs, were optimized within frameworks of P4mm (tetragonal) and R3m (rhombohedral) structures, and their total energies (Etetra and Erhombo, respectively) were compared. In BiMO3, except for BiGaO3, the total energy difference ΔE (≡Erhombo-Etetra) as a function of the tolerance factor t increases monotonically and smoothly, and the critical value from negative to positive in ΔE is about 1.00. In BiGaO3 with d10-state Ga ions, the tetragonal structure is more stable despite t<1.00. This result is due to the strong Coulomb repulsion between Ga 3s, 3p, and 3d states and O 2p states, which is consistent with tetragonal BiZn0.5Ti0.5O3 recently reported. In BaMO3, on the other hand, the dependence of ΔE is more complicated, that is, positive, zero [i.e., cubic (Pm3m)], negative, and positive, as t increases. The trend of the above calculated results is consistent with that of experimantal results, and can be a principal guideline for material design. The above crystal structures of AMO3 (A=Bi or Ba) are found to be closely related to the contribution of A ions to the local electric fields at M ions by the analysis of Lorentz corrections.