Interfacial Energy Barrier Research Articles

Elimination of Interface Energy Barriers Using Dendrimer Polyelectrolytes with Fractal Geometry.

In this work we study conjugated polyelectrolyte (CPE) films based on polyamidoamine (PAMAM) dendrimers of generations G1 and G3. These fractal macromolecules are compared to branched polyethylenimine (b-PEI) polymer using methanol as the solvent. All of these materials present a high density of amino groups, which protonated by methoxide counter-anions create strong dipolar interfaces. The vacuum level shift associated to these films on n-type silicon was 0.93 eV for b-PEI, 0.72 eV for PAMAM G1 and 1.07 eV for PAMAM G3. These surface potentials were enough to overcome Fermi level pinning, which is a typical limitation of aluminium contacts on n-type silicon. A specific contact resistance as low as 20 mΩ·cm2 was achieved with PAMAM G3, in agreement with the higher surface potential of this material. Good electron transport properties were also obtained for the other materials. Proof-of-concept silicon solar cells combining vanadium oxide as a hole-selective contact with these new electron transport layers have been fabricated and compared. The solar cell with PAMAM G3 surpassed 15% conversion efficiency with an overall increase of all the photovoltaic parameters. The performance of these devices correlates with compositional and nanostructural studies of the different CPE films. Particularly, a figure-of-merit (Vσ) for CPE films that considers the number of protonated amino groups per macromolecule has been introduced. The fractal geometry of dendrimers leads to a geometric increase in the number of amino groups per generation. Thus, investigation of dendrimer macromolecules seems a very good strategy to design CPE films with enhanced charge-carrier selectivity.

Multiscale Interfacial Interactions in Carbon Nanotube–Asphalt Nanocomposites: Implications for Asphalt Pavement Materials

Carbon nanotube (CNT)–asphalt nanocomposites are considered to be the next generation of pavement materials; however, the interaction between CNT and asphalt at the interface and the mechanisms of property enhancement are not well understood, which limits the application of CNT–asphalt nanocomposites. In this study, CNT is used as a representative of one-dimensional nanomaterials, and the interfacial multiscale interaction mechanism between CNT and asphalt molecules is investigated by density functional theory (DFT), molecular dynamics simulation, atomic force microscopy (AFM), gelation permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and performance evaluation. It has been shown that CNT and asphalt substrates are very compatible at the atomic scale, mainly due to π–π stacking, mechanical entanglement, and van der Waals forces. The interfacial energy barrier is −2.63 (kcal/mol)/Å2 and the shear barriers are 52.70 MPa, with asphaltene and aromatic making the greatest contribution to interfacial stress transfer. This research provides a theoretical basis for the targeted tuning of properties and establishes the basis for CNT–asphalt nanocomposites for highway applications.

Transport Layer Engineering by Hydrochloric Acid for Efficient Perovskite Solar Cells with a High Open-Circuit Voltage

A large number of defect states that exist at the interface between a perovskite film and an electron transport layer (ETL) are detrimental to the efficiency and the stability of perovskite solar cells (PSCs). It is still a challenge to simultaneously passivate the defects on both sides by a stable and low-cost ion compound. Herein, we demonstrate a simple and effective versatile strategy by introducing hydrochloric acid into SnO2 precursor solution to passivate the defects in both SnO2 and perovskite layers and simultaneously reduce the interface energy barrier, ultimately achieving a high-performance and hysteresis-free PSCs. Hydrogen ions can neutralize -OH groups on the SnO2 surface, whereas the Cl- can not only combine with Sn4+ in ETL but also suppress the Pb-I antisite defects formed at the buried interface. The reduced nonradiative recombination and the favorable energy level alignment result in a significantly increased efficiency from 20.71 to 22.06% of PSCs due to the enhancement of open-circuit voltage. In addition, the stability of the device can also be improved. This work presents a facile and promising approach for the development of highly efficient PSCs.

High thermoelectric performance in ZrNiSn through electron injection and boosting carrier mobility

Inert insulating oxides have been used as phonon scattering centers to reduce the lattice thermal conductivity of half-Heusler thermoelectric materials, but they often cause a decline in electrical transport performance. In this work, the in-situ conductive semi-metal ZrTe2 makes 15% decreased thermal conductivity and 42% increased electrical conductivity in ZrNiSn simultaneously. When the phase boundary scatters the mid-long wavelength phonons, it is not an obstacle for the electrons. Thanks to the decreased interfacial energy barrier and high mobility electron injection from ZrTe2, even when the charge carrier concentration increases by 56% due to the in-situ ZrTe2 induced bandgap decreasing, 190% improved mobility is also obtained. High zT ∼0.9 is achieved at 873 K in 4 at.% Te composited ZrNiSn through electron injection and boosting carrier mobility. These results have suggested a promising way to decouple the electron and phonon transport behaviors via forming the in-situ conductive secondary phase.

Steered electrical pathways of plasmonic metal-semiconductor heterostructures via crystal-phase-dependent selective deposition

Plasmon mediated heterojunction with tunable and superior photoelectrical performance is an intriguing approach to improve light harvesting in photocatalysis. However, the low separation efficiency and uncertain diffusion directions of charges remained still a challenge to meet desired photocatalytic process. To overcome these issues, in this work, we showed the crystal-phase-dependent effects of the semiconductor for hot-electrons transfer assisted by plasmonic heterostructures under visible light by using Au–P25 as a model. It was found that Au–P25 formed by Au-anatase-rutile was greatly advantageous over that of Au-rutile-anatase for the hot-electrons separation and transportation (∼3 folds increase in photocurrents density). Such differences may account for the suitable band alignment mediated by selective crystal phase contact, which forming a convenient pathway for fluent electrons transfer caused by the smaller interfacial energy barrier in Au-anatase-rutile, comparing to that in Au-rutile-anatase. Such results might offer some useful contributions to the future design of nanomaterials for plasmon-mediated photoelectrical or photochemical applications.

Dual Optimization of Bulk and Interface via the Synergistic Effect of Ligand Anchoring and Hole Transport Dopant Enables 23.28% Efficiency Inverted Perovskite Solar Cells

The crystalline morphology of perovskite film plays a key role in determining the stability and performance of perovskite solar cells (PSCs). In addition, the work function and conductivity of hole transport layer (HTL) have a great influence on the effciency of PSCs. Here, we develop a synergistic doping strategy to fabricate high-performance inverted PSCs, doping a functional nanographene (C78-AHM) into the poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) HTL, thus forming an HTL with higher conductivity, lower roughness, and frontier energy levels matching the perovskite absorber work function. On this basis, thiosemicarbazide (TSC) was doped into the precursor solution of perovskite as the grain and interface modifier to further improve the crystalline morphology of perovskite film. Compared with the current single passivation method, this codoping strategy can simultaneously reduce the surface and bulk defects of perovskite film and reduce the interface energy barrier. Eventually, high-quality TSC-doped perovskite films based on C78-AHM-doped PTAA HTL are obtained with over 2 μm sized grains, pinhole-free, and improved crystallinity. As a result, this synergistic doping strategy increases the efficiency of the device from 20.27% to 23.28%. Furthermore, the environmental and thermal stabilities of the devices are significantly improved. Therefore, this work provides a simple way for the preparation of other efficient optoelectronic devices.

Temperature-dependent slip length for water and electrolyte solution

HypothesisThe temperature dependence of boundary slip at liquid–solid interface is critical both for the fundamental theory and applications of fluid mechanics on micro and nanoscale, such as sustainable cooling of electronic devices. However, there is a controversy on the temperature dependence of boundary slip which lacks experimental evidence, we aim to resolve it by hypothesizing that the temperature dependent slip length depends on the variation in the interfacial energy barrier. ExperimentsHere, we measured ls – T relation of water and NaCl solution on self-assembled FDTS (Perfluorodecyltrichlorosilane) surface using colloidal probe AFM. The transition of ls – T monotonicity is found. For water and 0.1 M NaCl solution, ls is negatively correlated with T, while for 1 M NaCl solution, ls is positively correlated with T. FindingsTogether with molecular dynamics simulations, such observation is quantitatively explained with an analytical model based on rate theory, where the ls – T monotonicity depends on the difference between liquid–solid interfacial energy barrier and liquid internal energy barrier. Our results provide not only solid experimental evidence for the boundary slip being a rate process, but also a basis for the thermal-hydrodynamic design of microfluidic and nanofluidic devices.

First principles study of V/Pd interface interactions and their hydrogen absorption properties

Hydrogen permeation through vanadium/palladium (V/Pd) metal composite membranes is an effective and practical method of separating hydrogen from gas mixtures. In order to gain an insight into the relation between the interfacial structure and hydrogen adsorption/diffusion properties of the catalytic Pd layer bonded to the metal membrane, and then improve the ability of the alloy membrane to purify hydrogen, the first principle based on the density functional theory is used to study the hydrogen adsorption/diffusion behavior at the V/Pd metal composite membrane interface. The results show that because the charge density at the V/Pd interface increases with the V/Pd bonding increasing, the dissolution energy of hydrogen atom (H) increases with it approaching to the interface, and it has the highest dissolution energy near the V/Pd interface (0.567 eV). Hydrogen migration energy barrier calculations show that compared with the maximum energy barrier for horizontal diffusion of H along the V/Pd interface (0.64 eV), the H vertical V/Pd interface energy barrier (0.56 eV) is small, thus H tends to migrate vertically V/Pd interface and diffuse from the Pd layer to the V substrate side. As the hydrogen solvation energy of the Pd layer at the V/Pd interface (0.238 eV) is higher than that on the V membrane side (–0.165 eV), H will gather on the V film side of the interface, which is easy to cause hydrogen to be embrittled. Calculations of Pd/Fe doping of the V matrix show that comparing with the undoped energy barrier (0.56 eV), Pd/Fe doping can significantly reduce the maximum energy barrier (0.45 eV/0.54 eV) in the diffusion path of the interface, which is favorable for hydrogen permeation and diffusion. And the doped interface can inhibit the interdiffusion of V layer and catalytic Pd layer to a certain extent, which improves the structural stability of the composite film.

Interfacial engineering between SnO2/MAPbI3by maleate pheniramine halides toward carbon counter electrode-based perovskite solar cells with 16.21% efficiency

Multifunctional complex molecules (CHM and BHM) were used to passivate interfacial defects, reduce the interfacial energy barrier, induce the orderly growth of perovskite crystals, and improve the PCE of HTL-free C-PSCs.

Breaking through the interfacial energy barrier limitations of type-I heterojunctions via ferroelectric polarization engineering: a case study of Bi5Ti3FeO15/BiOCl

The band structure of a heterojunction significantly affects its photocharge separation efficiency.

A trifunctional polyethylene oxide buffer layer for stable and efficient all-inorganic CsPbBr3 perovskite solar cells.

Carbon-based all-inorganic perovskite solar cells have attracted growing interest owing to their simple fabrication process, low cost, and high stability in air. On account of the large interfacial energy barriers and polycrystalline features of perovskite films, the carrier interface recombination and inherent defects in the perovskite layer are still great challenges in further increasing the power conversion efficiency and stability of carbon-based PSCs. We present here a trifunctional polyethylene oxide buffer layer at the perovskite/carbon interface to promote the PCE and stability of carbon-based all-inorganic CsPbBr3 PSCs: (i) the PEO layer increases the crystallinity of inorganic CsPbBr3 grains for low defect state density; (ii) the oxygenic groups in PEO chains passivate the defects on the perovskite surface; and (iii) the long hydrophobic alkyl chains improve the stability in moisture. The best encapsulated PSC achieves a PCE of 8.84% and maintains 84.8% of its initial efficiency in air with 80% RH over 30 days.

Thermal-inert and ohmic-contact interface for high performance half-Heusler based thermoelectric generator

Unsatisfied electrode bonding in half-Heusler devices renders thermal damage and large efficiency loss, which limits their practical service at high temperatures. Here, we develop a thermodynamic strategy to screen barrier layer elements. Theoretically, we found that the interface between VIIB elements and half-Heuslers possesses near-zero interfacial reaction energy and large atomic diffusion barrier. Experimentally, such an interphase proves to be the atomic direct bonding and has high thermal stability at 1073 K, leading to ideal ohmic contact. Such thermally inert and ohmic contact interface enable modules stably to work at elevated temperature up to 1100 K, which releases the peak performance of half-Heuslers and in turn boosts the energy conversion efficiencies to the records of 11.1% and 13.3% for half-Heusler single-stage and half-Heusler/Bi2Te3 segmented modules. This design strategy provides a feasible solution for the high-temperature half-Heusler generators and gives enlightenment for other package interconnection design of electronic devices.

Interfacial energy barrier tuning of hierarchical Bi2O3/WO3 heterojunctions for advanced triethylamine sensor

Traditional triethylamine (TEA) sensors suffer from the drawback of serious cross-sensitivity due to the low charge-transfer ability of gas-sensing materials. Herein, an advanced anti-interference TEA sensor is designed by utilizing interfacial energy barriers of hierarchical Bi2O3/WO3 composite. Benefiting from abundant slit-like pores, desirable defect features, and amplification effect of heterojunctions, the sensor based on Bi2O3/WO3 composite with 40% Bi2O3 (0.4-Bi2O3/WO3) demonstrates remarkable performance in terms of faster response/recovery time (1.7-fold/1.2-fold), higher response (2.1-fold), and lower power consumption (30 °C-decrement) as compared with the pristine WO3 sensor. Furthermore, the composite sensor exhibits long-term stability, reproducibility, and negligible response towards interfering molecules, indicating the promising potential of Bi2O3/WO3 heterojunctions in anti-interference detection of low-concentration TEA in real applications. This work not only offers a rational solution to design advanced gas sensors by tuning the interfacial energy barriers of heterojunctions, but also provides a fundamental understanding of hierarchical Bi2O3 structures in the gas-sensing field.

Highly efficient and stable hole-transport-layer-free inverted perovskite solar cells achieved 22% efficiency through p-type molecular synergistic doping

low-cost, facile manufacturing processes are becoming more and more important for commercialization of perovskite solar cells (PSCs). In this aspect, the development of hole-transport-layer-free (HTL-free) PSC is particularly important. In this paper, we fabricated HTL-free PSC with improved photovoltaic performance via synergistic doping Cu(thiourea)Cl (Cu(Tu)Cl) and thiosemicarbazide into the perovskite precursor solution to obtain high-quality perovskite films with average grains of more than 1 µm. This synergistic doping strategy can simultaneously decrease perovskite surface and internal defects and mitigate interfacial energy barrier, which is superior to the present single passivation method which brings about defect passivation deficiency. As a result, compared to the control device with the efficiency of 13.10%, the HTL-free perovskite device prepared by synergistic doping strategy achieves a remarkable PCE of 22% with almost negligible hysteresis, which is the highest PCE values reported so far for the HTL-free PSCs. In addition, the environmental, thermal and long-term operational stabilities of the optimized devices prepared by synergistic doping strategy are significantly improved compare to the control devices. Especially, the unencapsulated optimized device retains 90% of the original efficiency under continuous illumination (100 mW cm−2) for 1000 h with the maximum power point (MPP) tracking in nitrogen-filled test box. Furthermore, this strategy has been shown to be effective in wide-bandgap perovskite. The wide-bandgap perovskite Cs0.05MA0.15FA0.8Pb(I0.75Br0.25)3 (1.65 eV) based HTL-free device achieves a PCE of 19.7% with an Voc of 1.2 V, which is the highest PCE values reported so far for the HTL-free wide-bandgap PSCs, which opens a new way to fabricate HTL-free perovskite-based tandem solar cells. This work manifests a noteworthy step towards the facile, cost-efficient fabricating of PSCs with both high efficiency and simple manufacturing processes.

Interface functionalization of composite electrolyte by Lix-CeO2 layer on the surface of Li6.4La3Zr1.4Ta0.6O12

The development of all-solid-state batteries has become an inevitable trend as safety is increasingly valued. Naturally, solid-state electrolytes(SSEs) have attracted extensive attention. The composite of superionic conductors and polymer is considered to be a material that can achieve both high energy density and safety. Nevertheless, the compatibility between the polymer and superionic conductors is poor due to the large differences in structure and electrochemistry, resulting in a high interfacial transport energy barrier of the cation. In this work, a functional Lix-CeO2(LCO) layer is synthesized on the surface of the superionic conductor. While broadening the cation transport path at the interface, the anion of lithium salt is successfully anchored and the concentration of lithium-ion is increased. In addition, the structural compatibility and adhesion between polymer and superionic conductors are improve. Compared with the pristine electrolyte, the ionic conductivity and the lithium-ion transference number (tLi+) of LLZTO@2%LCO are as high as 2.325 × 10−3 S cm−1(pristine sample is only 7.109 × 10−5 S cm−1) and 0.44 (pristine sample is only 0.27)respectively. At 2C, the discharge specific capacity of LiFePO4(LFP)|LLZTO@2%LCO-CSE|Li can reach 134.8mAh g−1. The outstanding performance of the composite electrolyte is attributed to the interface functionalized Lix-CeO2 compound coating. Therefore, polymer/ceramic interface engineering to promote the interaction between the two components should be one of the directions of future research.

Synthesis of highly dispersed TiO2 NPs/GO composites sol and its application in inverted perovskite solar cells

The poor dispersion property and agglomerate of TiO 2 /graphene oxide (GO) composites greatly limit its application in optoelectronic devices. Here, low-temperature processed, high dispersion TiO 2 nanoparticles/GO (TiO 2 NPs/GO) sol was synthesized via modified sol-gel strategy combing by a hydrothermal process. The formation mechanism of TiO 2 NPs/GO sol is investigated and the results show that the TiO 2 NPs can be embedded to GO sheet with Ti–O–C chemical bond via dehydration condensation reaction between the hydroxyl groups on the surfaces of them. In addition, there are charge transportation between TiO 2 NPs and GO is confirmed, which benefits to enhance the charge transport efficiency of TiO 2 NPs. Using TiO 2 NPs/GO composite as cathode interface, the energy barrier of cathode interface is eliminated, and the hysteresis effect is largely suppressed. The highest power conversion efficiency (PCE) of 17.73% is achieved with TiO 2 NPs/GO, and the average PCE is also enhanced by 14.71% comparing to the control devices. This simple strategy light on the preparation high dispersive TiO 2 NPs/GO composites and correspondingly applied in inverted PSCs to enhance the interface contact. • Low-temperature processed, high dispersive TiO 2 NPs/GO composite sol has been synthesized. • The interface energy barrier and hysteresis are eliminated with TiO 2 NPs/GO interface modification. • The highest power conversion efficiency (PCE) of 17.73% is achieved.

NMR Study of Lithium Transport in Liquid-Ceramic Hybrid Solid Composite Electrolytes.

Despite their high conductivity, factors such as being fragile enough to face processing issues and interfacial incompatibility with lithium electrodes are some of the main drawbacks hindering the commercialization of inorganic (mainly oxide-based) solid electrolytes for use in all-solid-state lithium batteries. To this end, strategies such as the addition of solid polymer electrolytes have been proposed to improve the electrode-electrolyte interface. Hybrid electrolytes, which are usually composed of ceramic particles dispersed in a polymer, generally have a better affinity with electrodes and higher ionic conductivity than pure inorganic electrolytes. However, a significant downside of this strategy is that differences in lithium transportability between electrolyte layers can result in the formation of a high interfacial energy barrier across the cell. One strategy to ensure sufficient "wetting" of ceramics is to incorporate a liquid electrolyte directly into the solid inorganic electrolyte resulting in the formation of a hybrid liquid-ceramic electrolyte. To this end, liquid-ceramic hybrid electrolytes were prepared by adding LiG4TFSI, a solvate ionic liquid (SIL), to garnet, NASICON, and perovskite-type ceramic electrolytes. Although SIL addition resulted in increased ionic conductivity, comparisons between the pure SIL and the hybrid systems revealed that improvements were due to the SIL alone. A thorough investigation of the hybrid systems by solid-state nuclear magnetic resonance (NMR) revealed little to no lithium exchange between the ceramic and the SIL. This confirms that lithium conductivity preferentially occurs through the SIL in these hybrid systems. The primary role of the ceramic is to provide mechanical strength.

Dually Modified Wide-Bandgap Perovskites by Phenylethylammonium Acetate toward Highly Efficient Solar Cells with Low Photovoltage Loss.

Wide-bandgap perovskites as a class of promising top-cell materials have shown great promise in constructing efficient perovskite-based tandem solar cells, but their intrinsic relatively low radiative efficiency results in a large open-circuit voltage (VOC) deficit and thereby limits the whole device performance. Reducing film flaws or optimizing interfacial energy level alignments in wide-bandgap perovskite devices can efficiently inhibit nonradiative recombination to boost device VOC and efficiency. However, the simultaneous regulation on both sides and their underlying mechanism are less explored. Herein, a bifunctional modification approach is proposed to optimize the wide-bandgap perovskite surface with an ultrathin layer of phenylethylammonium acetate (PEAAc) to synchronously decrease the surface imperfection and mitigate the interfacial energy barrier. This treatment effectively heals under-coordinated surface defects through the formation of chemical interaction between the perovskite and PEAAc, bringing about a much slower charge trapping process and dramatically decreasing nonradiative recombination losses. Meanwhile, the passivation-induced upshifted Fermi level of the perovskite contributes to accelerated electron extraction and larger Fermi-level splitting under illumination. Consequently, the PEAAc-modified wide-bandgap (1.68 eV) device achieves an optimal efficiency of 20.66% with a high VOC of 1.25 V, among the highest reported VOC values for wide-bandgap perovskite devices, enormously outperforming that (18.86% and 1.18 V) of the device without passivation. In addition, the radiative limit of VOC for both cells is determined to be 1.42 V, delivering nonradiative recombination losses of 0.24 and 0.17 V for the control and PEAAc-modified devices, respectively. These results highlight the significance of the bifunctional modification strategy in achieving high-performance wide-bandgap perovskite devices.

Tailoring multifunctional anion modifiers to modulate interfacial chemical interactions for efficient and stable perovskite solar cells

The further development of perovskite solar cells (PSCs) is still restricted by high grain boundary density, interfacial defects, and interfacial energy barrier. Herein, we report a simple and effective universal anion modification strategy to increase the photovoltaic performance of PSCs, which is implemented through incorporating a series of guanidinium salts containing different anions (guanidinium thiocyanate (GASCN), guanidinium sulfate (GASO4), guanidine acetate (GAAc) and guanidine chloride (GACl)) to modify perovskite/SnO2 interface. All anions play a positive role in passivating the defects from surfaces of both SnO2 and perovskite layers, optimizing interfacial energy band alignment and facilitating the crystallization of PbI2 and perovskite. Moreover, different degrees of positive actions are found for different modifiers, which can be modulated by rational tailoring of anion species and thus interfacial chemical interaction. The relationships between chemical interaction strength, defect density, energy level, carrier lifetimes, crystallinity and device performance are established. The GASCN-, GA2SO4-, GAAc- and GACl-modified devices achieve a PCE of 22.76% 23.43%, 23.57% and 23.74%, respectively, which are much higher than 21.84% of the control device. Our obtained champion efficiency is among the highest efficiencies reported for the devices fabricated by sequential deposition method. Moreover, thermal and ambient stabilities are ameliorated after interface modification.

Study of Lead-Free Perovskite Photoelectric Devices with TiO2 as a Buffer Layer

In this work, a titanium oxide buffer layer was explored as a possible buffer electron transporting layer (ETL) with iodine-tin-based perovskite material for enhancement of a thin-film lead-free perovskite solar cell. The open-circuit voltage of the device was used as an indicator for the interface energy barrier’s change with the thickness of the TiO2. The buffer and photoabsorbing layers were deposited by vacuum reactive sputtering and a low-temperature ion-assisted process from a confocal sintered source, respectively, allowing precise tuning of the film properties and reproducibility of the solar cell behavior. The surface roughness of the buffer layers was investigated by atomic force microscopy and together with the measured absorbance spectra conclusions about the optical losses in the device were made. It was found that the highest voltage was generated from the structure with 75 nm-thick ETL. The electrical behavior of the cell with this buffer layer was additionally studied by impedance measurements. Small interface capacitance and contact resistance were obtained and considered suitable for photodetector fabrication. The practical applicability of the structure with a dual function of self-powered photodetection was demonstrated by the measurement of the response time.