Energy Mismatch Research Articles

Oxygen doping in nickel oxide for highly efficient planar perovskite solar cells

The presence of oxygen decreased the energy mismatch between NiO and perovskites, and led to a final efficiency of 19.2%.

Origin of Concentration Quenching in Ytterbium Coordination Polymers: Phonon‐Assisted Energy Transfer

Phonons are important in energy transfer for compensating the energy mismatch between a donor and an acceptor. In inorganic hosts doped with lanthanides, phonon‐assisted energy transfer can lead to quenching by a direct transfer of the energy to the phonon mode of the acceptor lanthanide. We demonstrate that this also applies to lanthanide coordination polymers and is the reason for the weak concentration quenching in this type of material. [YbxGd1–x(hfa)3dpbp]n [x = 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1; hfa: hexafluoroacetylacetonate, dpbp: 4,4′‐bis(diphenylphosphoryl)biphenyl] coordination polymers have been synthesized and their photophysical properties investigated. The single‐exponential emission lifetimes of Yb3+ gradually decreased with increasing concentration of Yb3+. Qualitative agreement was achieved between the experimental and theoretical lifetimes by using the phonon‐assisted energy‐transfer‐induced quenching model, which indicates that the origin of the concentration quenching in the coordination polymers is phonon‐assisted energy transfer.

An experimental study on storing thermal energy in packed beds with saturated steam as heat transfer fluid

Large number of solar thermal power plants operating or being designed use steam as a working fluid or heat transfer fluid. Therefore, a thermal energy storage (TES) system which can directly store the energy from steam can improve the demand-supply mismatch of thermal or electrical energy. Packed bed TES systems with solid rocks as packing material are one of the most economical and robust energy storage solutions available. This study investigates thermal energy storage process in packed bed systems with steam as heat transfer fluid (HTF). Experiments were conducted to understand thermal response of cylindrical packed bed filled with uniform and chemically inert alumina particles upon saturated steam injection along the axial direction. Axial thermal gradients determine the efficiency of the storage process. Saturated steam is introduced at different flow rates leading to different thermal gradients in the axial direction during different stages of thermal storage process. Rate of steam injection significantly impacts the modes of heat transfer– advection and diffusion. These experimental studies were extended with air as a HTF to compare thermal gradients in the bed under extremely different heat injection rates. In case of steam injection, wall heat loss rate is significantly lower than heat injection rate whereas, wall heat loss rate is comparable to heat injection rate in case of hot air injection.

Aqueous Solvation of Ammonia and Ammonium: Probing Hydrogen Bond Motifs with FT-IR and Soft X-ray Spectroscopy.

In a multifaceted investigation combining local soft X-ray and vibrational spectroscopic probes with ab initio molecular dynamics simulations, hydrogen-bonding interactions of two key principal amine compounds in aqueous solution, ammonia (NH3) and ammonium ion (NH4+), are quantitatively assessed in terms of electronic structure, solvation structure, and dynamics. From the X-ray measurements and complementary determination of the IR-active hydrogen stretching and bending modes of NH3 and NH4+ in aqueous solution, the picture emerges of a comparatively strongly hydrogen-bonded NH4+ ion via N-H donating interactions, whereas NH3 has a strongly accepting hydrogen bond with one water molecule at the nitrogen lone pair but only weakly N-H donating hydrogen bonds. In contrast to the case of hydrogen bonding among solvent water molecules, we find that energy mismatch between occupied orbitals of both the solutes NH3 and NH4+ and the surrounding water prevents strong mixing between orbitals upon hydrogen bonding and, thus, inhibits substantial charge transfer between solute and solvent. A close inspection of the calculated unoccupied molecular orbitals, in conjunction with experimentally measured N K-edge absorption spectra, reveals the different nature of the electronic structural effects of these two key principal amine compounds imposed by hydrogen bonding to water, where a pH-dependent excitation energy appears to be an intrinsic property. These results provide a benchmark for hydrogen bonding of other nitrogen-containing acids and bases.

Techno-economic analysis of the viability of residential photovoltaic systems using lithium-ion batteries for energy storage in the United Kingdom

Rooftop photovoltaic systems integrated with lithium-ion battery storage are a promising route for the decarbonisation of the UK’s power sector. From a consumer perspective, the financial benefits of lower utility costs and the potential of a financial return through providing grid services is a strong incentive to invest in PV-battery systems. Although battery storage is generally considered an effective means for reducing the energy mismatch between photovoltaic supply and building demand, it remains unclear when and under which conditions battery storage can be profitably operated within residential photovoltaic systems. This fact is particularly pertinent when battery degradation is considered within the decision framework. In this work, a commercially available coupled photovoltaic lithium-ion battery system is installed within a mid-sized UK family home. Photovoltaic energy generation and household electricity demand is recorded for more than one year. A comprehensive battery degradation model based on long-term ageing data collected from more than fifty long-term degradation experiments on commercial Lithium-ion batteries is developed. The comprehensive model accounts for all established modes of degradation including calendar ageing, capacity throughput, ambient temperature, state of charge, depth of discharge and current rate. The model is validated using cycling data and exhibited an average maximum transient error of 7.4% in capacity loss estimates and 7.3% in resistance rise estimates for over ayear of cycling. The battery ageing model is used to estimate the cost of battery degradation associated with cycling the battery according to the power profile logged from the residential property. A detailed cost-benefit analysis using the data collected from the property and the battery degradation model shows that, in terms of utility savings and export revenue, the integration of a battery yields no added benefit. This result was, in-part, attributed to the relatively basic control strategy and efficiency of the system. Furthermore, when the cost of battery degradation is included, the homeowner is subject to a significant financial loss.

Non-Hermitian matter-wave mixing in Bose-Einstein condensates: Dissipation-induced amplification

We investigate the nonlinear scattering dynamics in interacting atomic Bose-Einstein condensates under non-Hermitian dissipative conditions. We show that by carefully engineering a momentum-dependent atomic loss profile one can achieve matter-wave amplification through four wave mixing in a one-dimensional quasi free-space setup - a process that is forbidden in the counterpart Hermitian systems due to energy mismatch. Additionally, we show that similar effects lead to rich nonlinear dynamics in higher dimensions. Finally, we propose a physical realization for selectively tailoring the momentum-dependent atomic dissipation. Our strategy is based on a two step process: (i) exciting atoms to narrow Rydberg- or metastable excited states, and (ii) introducing loss through recoil; all while leaving the bulk condensate intact due to protection by quantum interference.

Tuning Surface Energy of Conjugated Polymers via Fluorine Substitution of Side Alkyl Chains: Influence on Phase Separation of Thin Films and Performance of Polymer Solar Cells.

Different contents of fluorine in side alkyl chains were incorporated into three conjugated polymers (namely, PBDTTT-f13, PBDTTT-f9, and PBDTTT-f5) whose backbones consist of benzodithiophene donors and thienothiophene acceptors. These three fluorinated polymers, in comparison with the well-known analogue PTB7-Th, show comparable energy levels and optical band gaps. However, the fluorination of side alkyl chains significantly changed the surface energy of bulk materials, which leads to distinctly different self-assembly behaviors and phase separations as being mixed with PC71BM. The increased mismatch in surface energies between the polymer and PC71BM causes larger scale phase domains, which makes a sound explanation for the difference in their photovoltaic properties.

High-Index Facets Bounded Platinum–Lead Concave Nanocubes with Enhanced Electrocatalytic Properties

High-index facets bounded platinum-based alloy nanocrystals usually exhibit enhanced electrocatalytic activity. However, the high surface energy, thermodynamic instability, and lattice mismatch make it a significant challenge to synthesize well-defined bimetallic nanocrystals with high-index facets. Here we developed a one-step wet-chemical synthesis of uniform PtPb concave nanocubes (CNCs) enclosed by {520} high-index facets. The as-prepared PtPb CNCs exhibited high synthetic yield and highly concave structure with an average size of 14 nm. Moreover, the synergistic effects and exposed {520} facets endowed the PtPb CNCs with excellent stability and electrocatalytic mass activity toward the methanol oxidation reaction (MOR), which was 2.16- and 4.62-times higher than PtPb nanocubes (NCs) and commercial Pt/C catalysts, respectively. This work provides a new way for rational design and practical application of efficient catalysts.

Porous RuO2 nanosheet/CNT electrodes for DMSO-based Li-O2 and Li ion O2 batteries

Two-dimensional (2D) porous RuO2 nanosheets are synthesized using graphene oxide as the template, on which numerous holes of a few nanometers in diameter are simultaneously created. The holey RuO2 nanosheets are rationally assembled with carbon nanotube (CNT) interlayers to form a hybrid with highly enhanced mass/electron transport through the conductive, porous structure. The 2D/1D hybrid electrodes deliver exceptional performance in Li-oxygen batteries (LOBs). The first-principle calculations combined with microscopy reveal that Li2O2 interacts strongly with RuO2 and thermodynamically follows a Stranski-Krastanov growth mode. The state hybridization transforms inherently insulative Li2O2 conductive, reducing the overpotentials encouraged by the Ohmic loss. The highly LiO2-soluble dimethyl sulfoxide-based electrolyte is employed for the first time to prepare Li ion oxygen batteries (LIOBs) through refining the solid-electrolyte interphase and concentrated electrolyte. This approach effectively mitigates the energy mismatch present between the lowest unoccupied molecular orbitals of electrolyte and the work functions of Si/C anode. The LIOBs with the developed RuO2/CNT hybrid electrodes deliver cyclic stability and ultrahigh gravimetric energy and power densities up to 1897Whkg−1 and 1396Wkg−1, respectively. This work offers new insights into designing highly porous 2D/1D oxygen catalysts together with highly LiO2-soluble electrolytes for high-performance LOBs/LIOBs.

Infrared and visible laser spectroscopy for highly-charged Ni-like ions

Application of visible or infrared (IR) lasers for spectroscopy of highly-charged ions (HCI) has not been particularly extensive so far due to a mismatch in typical energies. We show here that the energy difference between the two lowest levels within the first excited configuration 3d94s in Ni-like ions of heavy elements from ZN=60 to ZN=92 is within the range of visible or near-IR lasers. The wavelengths of these transitions are calculated within the relativistic model potential formalism and compared with other theoretical and limited experimental data. Detailed collisional-radiative simulations of non-Maxwellian and thermal plasmas are performed showing that photopumping between these levels using relatively moderate lasers is sufficient to provide a two-order of magnitude increase of the pumped level population. This accordingly results in a similar rise of the X-ray line intensity thereby allowing control of X-ray emission with visible/IR lasers.

Few-body interactions in frozen Rydberg gases

The strong dipole-dipole coupling and the Stark tunability make Forster resonances an attractive tool for the implementation of quantum gates. In this direction a generalization to a N-body process would be a powerful instrument to implement multi-qubit gate and it will also path the way to the understanding of many-body physics. In this review, we give a general introduction on Forster resonances, also known as two-body FRET, giving an overview of the different application in quantum engineering and quantum simulation. Then we will describe an analogous process, the quasi-forbidden FRET, which is related to the Stark mixing due to the presence of an external electric field. We will then focus on its use in a peculiar four-body FRET. The second part of this review is focused on our study of few-body interactions in a cold gas of Cs Rydberg atoms. After a detailed description of a series of quasi-forbidden resonances detected in the proximity of an allowed two-body FRET we will show our most promising result: the observation of a three-body FRET. This process corresponds to a generalization of the usual two-body FRET, where a third atom serves as a relay for the energy transport. This relay also compensates for the energy mismatch which prevents a direct two-body FRET between the donor and the acceptor, but on the other side allowed a three-body process; for this reason, the three-body FRET observed is a “Borromean” process. It can be generalized for any quantum system displaying two-body FRET from quasi-degenerate levels. We also predict N-body FRET, based on the same interaction scheme. Three-body FRET thus promises important applications in the formation of macro-trimers, implementation of few-body quantum gates, few-body entanglement or heralded entanglement.

Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer.

The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

Fabrication of p-Type La: Fe2O3 as Photocathode Via Atomic Layer Deposition

P-type La: Fe2O3 and the n-p junction of Fe2O3/La: Fe2O3 have been fabricated by ALD technique for its excellent conformability and controllable film growth with low defect densities. La: Fe2O3 film is demonstrated with p-type characteristics by Mott−Schottky plots and the hole concentration is calculated ~ 1.97 × 1015 cm-3. It also obtains a cathodic photocurrent ~28 μA/cm2 at -0.8 V vs. Ag/AgCl. When forming the n-p junction of Fe2O3/La: Fe2O3, it is found that the onset potentialexhibits a negative shift of ~150 mV and the photocurrent densities increases from 0.62 mA/cm2 to 1.31 mA/cm2 at 0.5 V vs. Ag/AgCl. Generally, the incident photon-to-current conversion efficiency (IPCE) of Fe2O3/La: Fe2O3 n-p junction reaches ~4.47% at 400 nm. Our results imply that it is desirable to tune the energy mismatch between water splitting potentials and the band edges of Fe2O3 by a facile surface modification by forming a solid n-p junction.

Fluorescent Carbon Nanotube Defects Manifest Substantial Vibrational Reorganization

Fluorescent defects have opened up exciting new opportunities to chemically tailor semiconducting carbon nanotubes for imaging, sensing, and photonics needs such as lasing, single photon emission, and photon upconversion. However, experimental measurements on the trap depths of these defects show a puzzling energy mismatch between the optical gap (difference in emission energies between the native exciton and defect trap states) and the thermal detrapping energy determined by application of the van ’t Hoff equation. To resolve this fundamentally important problem, here we synthetically incorporated a series of fluorescent aryl defects into semiconducting single-walled carbon nanotubes and experimentally determined their energy levels by temperature-dependent and chemically correlated evolution of exciton population and photoluminescence. We found that depending on the chemical nature and density of defects, the exciton detrapping energy is 14–77% smaller than the optical gap determined from photoluminesce...

Plasmonic enhancement of UV emission from ZnO thin films induced by Al nano-concave arrays

Surface plasmons (SPs) supported by Al nano-concave arrays with increasing interpore distance (Dc) were used to enhance the ultraviolet light emission from ZnO thin films. Two sets of samples were prepared: in the first set the thin ZnO films were deposited directly on Al nanoconcaves (the Al/ZnO samples) and in the second set a 10nm − Al2O3 spacer was placed between the textured Al and the ZnO films (the Al/Al2O3-ALD/ZnO samples). In the Al/ZnO samples the enhancement was limited by a nonradiative energy dissipation due to the Ohmic loss in the Al metal. However, for the ZnO layer deposited directly on Al nanopits synthesized at 150V (Dc=333±18nm), the largest 9-fold enhancement was obtained by achieving the best energy fit between the near band-edge (NBE) emission from ZnO and the λ(0,1) SPP resonance mode. In the Al/Al2O3-ALD/ZnO samples the amplification of the UV emission was smaller than in the Al/ZnO samples due to a big energy mismatch between the NBE emission and the λ(0,1) plasmonic mode. The results obtained in this work indicate that better tuning of the NBE − λ(0,1) SPP resonance mode coupling is possible through a proper modification of geometrical parameters in the Al/Al2O3-ALD/ZnO system such as Al nano-concave spacing and the thickness of the corresponding layer. This approach will reduce the negative influence of the non-radiative plasmonic modes and most likely will lead to further enhancement of the SP-modulated UV emission from ZnO thin films.

Quantum Phase Transitions with Parity-Symmetry Breaking and Hysteresis.

Symmetry-breaking quantum phase transitions play a key role in several condensed matter, cosmology and nuclear physics theoretical models1-3. Its observation in real systems is often hampered by finite temperatures and limited control of the system parameters. In this work we report for the first time the experimental observation of the full quantum phase diagram across a transition where the spatial parity symmetry is broken. Our system is made of an ultra-cold gas with tunable attractive interactions trapped in a spatially symmetric double-well potential. At a critical value of the interaction strength, we observe a continuous quantum phase transition where the gas spontaneously localizes in one well or the other, thus breaking the underlying symmetry of the system. Furthermore, we show the robustness of the asymmetric state against controlled energy mismatch between the two wells. This is the result of hysteresis associated with an additional discontinuous quantum phase transition that we fully characterize. Our results pave the way to the study of quantum critical phenomena at finite temperature4, the investigation of macroscopic quantum tunneling of the order parameter in the hysteretic regime and the production of strongly quantum entangled states at critical points5.

Synthesis and characterization of poly(3-hexylthiophene)-block-poly(dimethylsiloxane) for photovoltaic application

A diblock copolymer poly(3-hexylthiophene)-block-poly(dimethylsiloxane) (P3HT-b-PDMS) was synthesized as a donor material for organic photovoltaic devices. The regioregular poly(3-hexylthiophene) (P3HT) with a bromo-terminal was prepared via Grignard metathesis polymerization, and poly(dimethylsiloxane) (PDMS) with a silane terminal was obtained by anionic polymerization. Finally, the coupling reaction of these homopolymers via hydrosilylation afforded P3HT-b-PDMSs with different lengths of the PDMS segment. Device evaluation of photovoltaic cells based on P3HT-b-PDMS blended with [6,6]-phenyl-C61-butylic acid methyl ester (PCBM) revealed that the incorporation of PDMS segment effectively increase the photocurrent compared to a P3HT/PCBM system. From AFM and SEM observations for P3HT-b-PDMS/PCBM blend films, it was clearly revealed that the phase-separated structure within several tens nanometer scale was obtained, and that the aggregation of PCBM was sufficiently suppressed by the introduction of PDMS. These facts indicate that the PDMS segment is probably assembled into the interface between P3HT and PCBM to relieve the mismatch of the surface free energy.

Molecular Tailoring for Efficient Conversion of Near-Infrared Light in Dye-Sensitized Solar Cellsoral

Dye-sensitized solar cells (DSCs) stand actually as a promising alternative to conventional silicon photovoltaic devices owing to lower production cost, low environmental footprint and unique properties to convert efficiently low light intensities and diffuse day light.( 1 ) Today more than 14 % power conversion efficiency (PCE) has been achieved by optimizing a cocktail of organic dye in conjunction with a Co+III/+IItris(1,10-phenanthroline) redox couple.( 2 ) So far, the current chemistry developed for DSC still present a lack in absorbing and converting substantially low-lying energy photons greater than λ >750 nm. With the aim to continue improving light harvesting capability of DSC for approaching closer to silicon standards, two important breakthroughs are needed: (i) reducing the internal energy loss arising from energy mismatch for electron injection and for dye regeneration (ii) extending light harvesting towards the NIR by the development of a new class of efficient sensitizers energetically well-coupled with the electronic properties of anatase TiO2 semi-conductor and electrolyte redox couple. We have developed a series of new efficient organic sensitizers based on squaraine core-units, croconines or cyanines which are able to shift towards the red the light absorption from ca. 520 nm from the current ruthenium polypyridil-based sensitizers to as high as 830 nm. These new sensitizers not only show NIR absorption but also exhibit significantly higher molar extinction coefficients (100 000 - 320 000 mol-1cm-1) while being cost competitive. This communication will describe these new efficient sensitizers converting up to 20% IPCE until 950 nm. Their light-to-electricity performances have been optimized by using highly diluted dye solution to promote aggregate-free self-assembled monolayer and carefully chosen electrolyte composition. Finally, the relationship between dye structure, electrolyte composition and the kinetic of charge transfers will be discussed on the basis of complementary set of techniques such as electrochemical impedance spectroscopy, time-correlated single photon-counting and ultra-fast pump-probe transient absorption spectroscopy. 1. B. O'Regan and M. Gratzel, Nature, 1991, 353, 737-740. 2. K. Kakiage, Y. Aoyama, T. Yano, K. Oya, J.-i. Fujisawa and M. Hanaya, Chem. Commun., 2015, 51, 15894-15897.

Nanocomposites of Hydrophobized Cellulose Nanocrystals and Polypropylene

Cellulose nanocrystals (CNCs) are high-strength sustainable nanomaterials, the incorporation of which to a host polymer matrix can potentially lead to nanocomposites with superior mechanical properties. However, the mismatch in surface energy of CNCs and common structural polymers is a challenge that needs to be overcome to prevent the aggregation of CNCs and ensure the robust integration of CNCs into a polymer matrix. Herein, we report an approach involving the functionalization of CNCs with maleated-anhydride polypropylene (MAPP) through diethylenetriamine (DETA) linkers to significantly enhance the compatibility between CNCs and polypropylene. Polypropylene/modified CNC nanocomposites displayed 74% and 76% increase in elastic modulus in comparison to neat polypropylene and polypropylene/untreated CNC nanocomposites, respectively. The tensile strength was also higher for nanocomposites withmodified CNC than neat polypropylene, as well as nanocomposites with untreated CNCs. The tensile strength at 5.5% strain of polypropylene/modified CNCnanocomposites was 32% and 28% larger that of polypropylene and polypropylene/untreated CNC nanocomposites, respectively. Finally, such CNC-based nanocomposites have a lower density than many competitive systems resulting in opportunities to propagate this environmentally-responsible technology to nanocomposites used in additive manufacturing, automotive applications, construction materials and consumer products.

Luminescence Properties of SrZrO3/Tb(3+) Perovskite: Host-Dopant Energy-Transfer Dynamics and Local Structure of Tb(3+).

SrZrO3 perovskite (SZP) was synthesized using gel-combustion route and characterized systematically using X-ray diffraction and time-resolved photoluminescence techniques. A detailed analysis of the optical properties of Tb(3+) ions in SrZrO3 was performed to correlate them with the local environment of the lanthanide ions in this perovskite. Photoluminescence (PL) spectroscopy showed that emission spectrum consists of host as well as Tb(3+) emission indicating the absence of complete host-dopant energy transfer. On the basis of emission spectrum and PL decay study it was also observed that Tb(3+) is not homogeneously distributed in SrZrO3 perovskite; rather, it is occupying two different sites. It is corroborated using extended X-ray absorption fine structure studies that Tb(3+) is stabilized on both six-coordinated Zr(4+) and eight-coordinated Sr(2) site. The energies calculated using density functional theory (DFT) indicates that Tb occupation in Sr site is energetically more favorable than Zr site. The analysis of valence charge distribution also substantiated our structural stability analysis of site-selective Tb doping in SrZrO3. Time-resolved emission spectroscopy is employed to elucidate the difference in the spectral feature of Tb(3+) ion at Sr(2+) and Zr(4+) site. DFT-calculated density of states analysis showed that energy mismatch of Tb-d states with Zr-d and O-p states of SZP makes the energy transfer from host SZP to Tb(3+) ion difficult.