Modification Of Energy Levels Research Articles

Regulating Charge Distribution in Porphyrin-Based Polymer for Achieving Photocatalytic CO2 Conversion to CH4 or C2H6.

The photocatalytic conversion of CO2 into products such as CH4 and C2H6 poses a significant challenge due to the lengthy reaction steps and the high energy barrier involved. In this study, both benzothiadiazole (BTD) and hydroxyl groups (-OH) are introduced into cobalt-based polymerized porphyrinic network (PPN) through a C-C coupling reaction. This modification of orbital energy levels that strengthens the ability of gain electrons and facilitates the charge transfer in PPN. Hydroxyl group largely enhances the ability for light response, while thiadiazole unit tunes the molecular orbital to proper energy level. By this way, BTD-DBP-PPN(Co) achieves the capability for CO2 conversion to CH4 and C2H6 under the irradiation of light. Co active site is introduced to reduce the energy barrier and facilitate the charge transfer. The reaction pathway for C2H6 production has been studied for further mechanism explanation. Overall, a series of cobalt-based porphyrin centers with a donor-acceptor (D-A) structure are designed and synthesized to enhance CO2 reduction performance and achieve the formation of C2 products under 300-W Xe lamp irradiation.

Anisotropy in Carbon Dioxide Adsorption on Forsterite.

In this study, density functional theory (DFT) method were used to investigate the adsorption behavior and binding mechanism of CO2 molecules on six crystallographic surfaces of forsterite (Mg2SiO4). The influence of surface crystallographic orientation on CO2 adsorption efficiency was examined at the atomic level. Results showed stable binding of CO2 on all surfaces. The interaction strength decreases in the order: (001) > (101) > (120) > (111) > (010) > (110), with the (001) surface exhibiting the highest binding capacity due to accessible magnesium cations interacting with CO2. Detailed electronic property analysis revealed significant charge transfer between CO2 oxygen atoms and surface magnesium atoms, driven by hybridization of oxygen 2p and magnesium 2s orbitals, leading to the formation of ionic and covalent bonds. These interactions stabilize the adsorbed CO2 and are accompanied by changes in the electronic structure, such as energy level shifts and modifications in the partial density of states (PDOS). The computational analysis provides a theoretical foundation for understanding CO2 binding mechanisms by forsterite. The findings highlight the importance of crystallographic orientation and electronic properties of the mineral surface in adsorption efficiency, contributing to a deeper understanding of CO2 interactions with mineral surfaces.

Charge Recombination and Transport Phenomena in Lead-Free Quantum Dot Solar Cells Probed by Impedance Spectroscopy

Due to their unique tunability and solution processability, the implementation of nanoscale semiconductor particles into optoelectronic devices is of increasing interest for future applications.1 Regarding the incorporation into solar cells, one of the most well-studied materials in form of quantum dots (QDs) is lead sulphide.1–3 However, due to its toxicity, replacing lead by a more environmentally friendly material would be immensely advantageous. In that context, ternary metal chalcogenides attracted a lot of interest, as many of them also provide a suitable band gap and high absorbance coefficients. One of the more prominent examples of that material class is AgBiS2.4 It has already been implemented in QD solar cells with remarkably high efficiencies, exceeding 8%.5 Nevertheless, detailed understanding of the charge recombination and transport processes in these devices still needs to be improved, especially with respect to the effect differences in surface passivation have on the aforementioned parameters.At the same time, impedance spectroscopy is a versatile technique that allows to probe the inductive, capacitive and resistive properties of a material or device over a wide range of time scales.6 However, it is a rarely employed method in this specific field of research.Therefore, it has been utilized here to study the recombination and transport properties in AgBiS2 QD solar cells to gain new insights into the underlying dynamics. Additionally, transient photovoltage and photocurrent measurements were employed to obtain an initial model and thus be able to reliably interpret the data from the impedance spectroscopy.As a result, it was found that changing the surface passivating treatment of the AgBiS2 QDs from iodide-containing compounds to bromide or chloride would improve the charge carrier lifetime and recombination resistance, while simultaneously the corresponding transport times exhibited a much less pronounced response. However, there were subtle differences found in the related transport resistances, which give rise to the hypothesis that there might be divergent mechanisms involved or even limiting charge transport depending on the exact surface composition of the QDs.Consequently, this study highlights the crucial importance of understanding the interplay of QD-ligand interaction in those hybrid systems, since it will significantly impact the overall material properties and thereby any device based on it. Furthermore, it demonstrates the suitability and value of employing impedance spectroscopy as a tool to probe for charge transport and recombination processes in this material.References Carey, G. H. et al. Colloidal Quantum Dot Solar Cells. Chem. Rev. 115, 12732–12763 (2015).Brown, P. R. et al. Energy level modification in lead sulfide quantum dot thin films through ligand exchange. ACS Nano 8, 5863–5872 (2014).Liu, M. et al. Hybrid organic-inorganic inks flatten the energy landscape in colloidal quantum dot solids. Nat. Mater. 16, 258–263 (2017).Bernechea, M. et al. Solution-processed solar cells based on environmentally friendly AgBiS2 nanocrystals. Nat. Photonics 10, 521–525 (2016).Wang, Y. et al. Cation disorder engineering yields AgBiS2 nanocrystals with enhanced optical absorption for efficient ultrathin solar cells. Nat. Photonics 16, 396 (2022).Von Hauff, E. Impedance Spectroscopy for Emerging Photovoltaics. J. Phys. Chem. C 123, 11329–11346 (2019).

Terbium doping and energy level modification of zirconium organic frameworks as probes for the improved determination of histamine and visual inspection of food freshness

Food safety is a common concern among people, and the development of high-performance food freshness detection technology is crucial, but is still highly challenging. Fluorescent sensing based on metal organic frameworks is a promising technology to tackle this issue. In this work, three UiO-66 type Zirconium organic frameworks (ZrOFs) which are functionalized with varying numbers of hydroxyl groups to alter the energy levels, and partial replacement of Zirconium(IV) by Terbium(III) ions to introduce additional emitting centers, were explored as probes for the sensing of Histamine (His). With one hydroxyl group introduced, UiO-66-OH@Tb can be developed as ratiometric fluorescent probe with improved sensing performance, showing a wide detection range of 0 to 120 mg/L, and a low detection limit of 0.13 mg/L. UiO-66-OH@Tb can also be fabricated into composite film to function as visual sensing material of His. This work can provide instructions for the development of other fluorescent sensors.

Efficient and Stable Perovskite Solar Cells by Tailoring of Interfaces.

The interface tailoring is crucial for the efficiency and stability of Perovskite Solar Cells (PSCs). The reported interface engineering primarily focuses on the energy level turning and trap state passivation to improve the photovoltaic performance of PSCs. In this review, molecule modifications are classified according to the basics of electron transfer mechanisms for the interface tailoring of materials. An in-depth analysis of energy level modification and trap passivation, as well as the universal Density Functional Theory (DFT) method employed in interface tailoring. In addition, strategies to address environmental protection and large-scale mini-modules fabrication by interface engineering are also discussed. This review can guide the researchers in understanding interface engineering to design interface materials for efficient, stable, and eco-friendly PSCs.

Modification of energy levels by cetyltrimethylammonium bromide at the perovskite/carbon interface for highly efficient and stable perovskite solar cells

Carbon electrodes represent a promising strategy for creating stable and low-cost perovskite solar cells (PSCs). However, PSCs with carbon electrodes usually suffer from energy level mismatch at the perovskite/carbon interface. In this study, the application of cetyltrimethylammonium bromide (CTABr) as a self-assembled monolayer (SAM) is explored to optimize the energy level alignment. As a result, CTABr-modified cell shows a 22.26% improvement in power conversion efficiency (PCE) and delivers an impressive PCE of 11.26% with a stabilized current density of 15.59 mA/cm2. Moreover, in a damp environment (humidity ≈85%) without encapsulation, CTABr-modified PSCs remain at 90% and 57% of the initial efficiency after being aged for 240 and 480 h, respectively. This study paves a new route for preparing better-performing PSCs with carbon using a low-temperature process.

Tuning product selectivity and visible-light-driven activity in oxidative coupling of amines to imines: A case study of BiOIxCl1−x photocatalyst

BiOCl has shown a promising photocatalytic activity in non-selective oxidation reactions, however its application in selective photocatalytic organic transformations is often limited by the strong oxidizing ability of photogenerated holes along with inefficient visible-light absorption. Herein, we showed that the poor visible-light-harvesting ability and low product selectivity of BiOCl in the selective oxidation of primary amines to corresponding imines can be alleviated by band energy level modification using a solid solution strategy. We combined an efficient visible light absorption performance of BiOI with a strong oxidizing ability of BiOCl to achieve BiOIxCl1−x solid solution catalysts with substantial improvements in imine yield. Among the BiOIxCl1−x catalysts, BiOI0.2Cl0.8 delivers the highest benzylamine conversion of ~84% with a selectivity of ~96% towards the imine, while pure BiOCl shows much lower conversion (~65%) and product selectivity (~81%). Such excellent performance could be attributed to electronic structure modifications induced by iodine atom incorporation into BiOCl structure as supported by UV–vis DRS, Mott-Schottky, and VB-XPS studies. Based on photoelectrochemical studies and material characterizations, band energy diagram of the BiOI0.2Cl0.8 is proposed and compared with that of pristine BiOCl and BiOI. Radical scavenging study, EPR spin trapping result, and Hammett plot suggest that the imine formation mechanism may occur via both 1O2- and O2•–-mediated pathways. This work highlights a rational catalyst design for which the benefits from each individual components are used to maximize photocatalytic performance toward the selective synthesis of value-added organic compounds.

Conjugated Random Terpolymer Donors towards High‐Efficiency Polymer Solar Cells

AbstractOver the past decades, polymer solar cells (PSCs) which contain conjugated polymers as electron donor and/or acceptor materials in active layers have achieved the power conversion efficiency (PCE) over 17%. Among them, tremendous alternative donor‐acceptor (D‐A) type conjugated copolymers have been reported as donor materials. Nevertheless, plenty of rooms still exist to further improve the photovoltaic performance for practical applications. Besides the exploration of the increasingly challenging novel D and/or A monomers to construct new D‐A copolymer donors, conjugated random terpolymer donors which involve a third existing monomer (D or A) provide an extra simple promising strategy to promote the photovoltaic performance to a higher level. Herein, recent progress on random terpolymer donors for efficient PSCs was reviewed. Firstly, random terpolymer donors were classified by several typical molecular building blocks. Then, the influences of the third monomer on various random terpolymers were highlighted according to the enhancement of light‐harvesting ability, modification of energy levels and optimization of the bulk‐heterojunction (BHJ) morphology. Finally, several issues which might be concerned in future research on random terpolymer donors were proposed. This review may be helpful for providing guidelines to design efficient random terpolymer donors as well as better‐understanding of the structure‐property‐performance correlations towards high performance PSCs via random terpolymer approach.

Controlling the energy gap of a tunable two-level system by ac drive

We study the influence of a strong off-resonant driving signal to the energy levels of a superconducting flux qubit both experimentally and theoretically. In the experiment, we carry out a three-tone spectroscopy. This allows us to directly observe the modification of the qubit's energy levels by the dynamical Stark shift caused by the driving signal. A theoretical treatment including corrections from both, rotating and counter-rotating frame, allowed us to completely explain the observed experimental results and to reconstruct the influence of the strong driving to the dissipative dynamics as well as to the coupling constants of the qubit. As one potential application, the tunability of the minimal energy-level splitting of a superconducting qubit by a microwave induced dynamical Stark shift can help to overcome the parameter spread induced by the micro fabrication of superconducting artificial quantum circuits.

Photosensitivity and charge injection dynamics of pentacene based thin-film transistors: influence of substrate temperature

In this work, we have performed an in-depth analysis to investigate the effect of substrate temperature on the molecular packing arrangement and energy levels of pentacene films. We have also explored their influence on the charge injection mechanism and photosensing behaviour of pentacene-based organic field-effect transistors (OFETs). In this study, we find the contact resistance and photosensitivity of the devices to be severely influenced by the active layer processing condition owing to the aforementioned structural and energy level modifications. Contact resistance of the devices at metal-semiconductor interfaces was observed to be reduced significantly upon increase in the substrate temperature; however, above a certain temperature, formation of pentacene thin-films was severely affected and no transistor characteristics were obtained afterwards. Detailed experimental analysis and theoretical investigations revealed that the processing temperature could strongly influence the grain structure and unit cell volume of the pentacene molecules, which consequently enhanced the carrier injection across the interface through a control over carrier mobility and the distribution of electronic states in the proximity of Fermi energy. Furthermore, our study demonstrates the role of substrate temperature in effectively enhancing the photosensitivity of the transistors. This report thus represents a step forward towards understanding a correlation between the processing temperature and the dynamics of charge injection in pentacene based organic transistors. The results also illustrate the viability of using proper substrate temperature to achieve an efficient photosensitivity from OFET devices. • Effect of substrate temperature on the charge injection dynamics is investigated. • Substrate temperature induced structural and energy level modification of pentacene is explored. • Delocalization of electronic states strongly influenced the interfacial charge injection. • High substrate temperature processed devices exhibited excellent photo sensitivity.

Efficient and Stable Perovskite Solar Cell with High Open-Circuit Voltage by Dimensional Interface Modification.

High-efficiency organic-inorganic hybrid perovskite solar cells have experienced rapid development and attracted significant attention in recent years. However, instability to an ambient environment such as moisture is a facile challenge for the application of perovskite solar cells. Herein, 1,8-octanediammonium iodide (ODAI) is employed to construct a two-dimensional modified interface by in situ combined with residual PbI2 on the formamidinium lead iodide (FAPbI3) perovskite surface. The ODA2+ ion seems to lie horizontally on the surface of a three-dimensional perovskite due to its substitution for two FA+ ions, which could protect the bulk perovskite more effectively. The unencapsulated perovskite solar cells showed notably improved stability, which remained 92% of its initial efficiency after storing in an ambient environment for 120 days. In addition, a higher open-circuit voltage of 1.13 V compared to that of the control device (1.04 V) was obtained due to the interface energy level modification and defect passivation. A champion power conversion efficiency of 21.18% was therefore obtained with a stabilized power output of 20.64% at the maximum power point for planar perovskite solar cells.

Highly Efficient and Stable Perovskite Solar Cells via Modification of Energy Levels at the Perovskite/Carbon Electrode Interface.

Perovskite solar cells (PSCs) have attracted great attention in the past few years due to their rapid increase in efficiency and low-cost fabrication. However, instability against thermal stress and humidity is a big issue hindering their commercialization and practical applications. Here, by combining thermally stable formamidinium-cesium-based perovskite and a moisture-resistant carbon electrode, successful fabrication of stable PSCs is reported, which maintain on average 77% of the initial value after being aged for 192 h under conditions of 85 °C and 85% relative humidity (the "double 85" aging condition) without encapsulation. However, the mismatch of energy levels at the interface between the perovskite and the carbon electrode limits charge collection and leads to poor device performance. To address this issue, a thin-layer of poly(ethylene oxide) (PEO) is introduced to achieve improved interfacial energy level alignment, which is verified by ultraviolet photoemission spectroscopy measurements. Indeed as a result, power conversion efficiency increases from 12.2% to 14.9% after suitable energy level modification by intentionally introducing a thin layer of PEO at the perovskite/carbon interface.

Metal Composition and Polyethylenimine Doping Capacity Effects on Semiconducting Metal Oxide-Polymer Blend Charge Transport.

Charge transport and film microstructure evolution are investigated in a series of polyethylenimine (PEI)-doped (0.0-6.0 wt%) amorphous metal oxide (MO) semiconductor thin film blends. Here, PEI doping generality is broadened from binary In2O3 to ternary (e.g., In+Zn in IZO, In+Ga in IGO) and quaternary (e.g., In+Zn+Ga in IGZO) systems, demonstrating the universality of this approach for polymer electron doping of MO matrices. Systematic comparison of the effects of various metal ions on the electronic transport and film microstructure of these blends are investigated by combined thin-film transistor (TFT) response, AFM, XPS, XRD, X-ray reflectivity, and cross-sectional TEM. Morphological analysis reveals that layered MO film microstructures predominate in PEI-In2O3, but become less distinct in IGO and are not detectable in IZO and IGZO. TFT charge transport measurements indicate a general coincidence of a peak in carrier mobility (μpeak) and overall TFT performance at optimal PEI doping concentrations. Optimal PEI loadings that yield μpeak values depend not only on the MO elemental composition but also, equally important, on the metal atomic ratios. By investigating the relationship between the MO energy levels and PEI doping by UPS, it is concluded that the efficiency of PEI electron-donation is highly dependent on the metal oxide matrix work function in cases where film morphology is optimal, as in the IGO compositions. The results of this investigation demonstrate the broad generality and efficacy of PEI electron doping applied to electronically functional metal oxide systems and that the resulting film microstructure, morphology, and energy level modifications are all vital to understanding charge transport in these amorphous oxide blends.

Measuring the Electronic Structure of Nanocrystal Thin Films Using Energy-Resolved Electrochemical Impedance Spectroscopy.

Use of nanocrystal thin films as active layers in optoelectronic devices requires tailoring of their electronic band structure. Here, we demonstrate energy-resolved electrochemical impedance spectroscopy (ER-EIS) as a method to quantify the electronic structure in nanocrystal thin films. This technique is particularly well-suited for nanocrystal-based thin films as it allows for in situ assessment of electronic structure during solution-based deposition of the thin film. Using well-studied lead sulfide nanocrystals as an example, we show that ER-EIS can be used to probe the energy position and number density of defect or dopant states as well as the modification of energy levels in nanocrystal solids that results through the exchange of surface ligands. This work highlights that ER-EIS is a sensitive and fast method to measure the electronic structure of nanocrystal thin films and enables their optimization in optoelectronic devices.

Contact engineering for efficient charge injection in organic transistors with low-cost metal electrodes

Controlling charge injection at the metal-semiconductor interface is very crucial for organic electronic devices in general as it can significantly influence the overall device performance. Herein, we report a facile, yet efficient contact modification approach, to enhance the hole injection efficiency through the incorporation of a high vacuum deposited TPD [N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine] interlayer between the electrodes and the active semiconducting layer. The device performance parameters such as mobility and on/off ratio improved significantly after the inclusion of the TPD buffer layer, and more interestingly, the devices with cost effective Ag and Cu electrodes were able to exhibit a superior device performance than the typically used Au source-drain devices. We have also observed that this contact modification technique can be even more effective than commonly used metal oxide interface modifying layers. Our investigations demonstrate the efficacy of the TPD interlayer in effectively reducing the interfacial contact resistance through the modification of pentacene energy levels, which consequently results in the substantial improvement in the device performances.

Radical induced intermolecular linkage and energy level modifications of a porphyrin monolayer.

A new method to directly modify the surface structure and energy levels of a porphyrin monolayer was examined in the molecular scale using scanning tunneling microscopy and spectroscopy (STM and STS) and presented in this communication. The exposure to atomic oxygen has induced highly ordered surface cross-linking and changed the occupied and unoccupied orbital levels of a cobalt(ii) octaethyl porphyrin (CoOEP) monolayer, and as a result, the HOMO-LUMO gap was reduced by ∼10%. Counterintuitively, the STM/STS data indicated that the reactive central Co atoms did not participate in the gas-surface reactions. Reflection-absorption infrared spectroscopy (RAIRS) measurements further indicated that the STM observed intermolecular linkages are stabilized via hydrogen bonding. This CoOEP + O˙ system also illustrates an example that the six-fold surface packing symmetry predominates the four-fold molecular symmetry in producing a three-fold symmetric surface cross-linking structure.

Tuning optical and three photon absorption properties in graphene oxide-polyvinyl alcohol free standing films

We report the optical and nonlinear optical properties of graphene oxide (GO)-polyvinyl alcohol (PVA) free standing films. The composite polymer films were prepared in ex-situ method. The variation in optical absorption spectra and optical constants with the amount of GO loading was noteworthy from the optical absorption spectroscopic studies. Nonlinear optical studies done at 532 nm using 5 ns laser pulses show three photon absorption like behaviour. Both steady state and time resolved fluorescence studies reveal that the GO was functioning as a pathway for the decay of fluorescence from PVA. This is attributed to the energy level modifications of GO through hydroxyl groups with PVA. Raman spectroscopy also supports the interaction between GO and PVA ions through OH radicals.

The band-gap enhanced photovoltaic structure

We critically examine the recently suggested structure that was postulated to potentially add 50% to the photo-conversion efficiency of organic solar cells. We find that the structure could be realized using stepwise increase in the gap as long as the steps are not above 0.1 eV. We also show that the charge extraction is not compromised due to an interplay between the contact's space charge and the energy level modification, which result in a flat energy band at the extracting contact.

Diketopyrrolopyrroles with a Distinct Energy Level Cascade for Efficient Charge Carrier Generation in Organic Solar Cells

Three structurally different low molecular weight diketopyrrolopyrroles (DPPs) are synthesized in order to provide donors with a precise offset in their energy levels. The DPPs are characterized for optical, electrochemical, and thermal properties. By changing the terminal aryl groups attached to the DPP core from phenyl over m‐pyridine to p‐pyridine, different solid state packing is observed in thin film studies using UV/VIS absorption spectra and X‐ray diffraction. Most importantly it is shown that both, reduction as well as oxidation potentials can be precisely tuned with a gradual stepping of about 100 meV by changing the terminal groups attached to the DPP core. Exploiting this energy level modification, these materials are tested in planar cascade organic photovoltaic devices using C60 as acceptor. A sub nm thick interlayer of a suitable DPP derivative is introduced to obtain a distinct energy level cascade at the donor/acceptor interface. Power conversion efficiency as well as short‐circuit current density is doubled with respect to the reference bilayer devices lacking the interface cascade. Spectrally resolved analysis of external quantum efficiency reveals that this enhancement can mainly be attributed to destabilization of bound charge transfer states formed in the C60 layer at the interlayer interface, thus reducing geminate recombination losses.

Tunable Photoluminescent Core/Shell Cu(+)-Doped ZnSe/ZnS Quantum Dots Codoped with Al(3+), Ga(3+), or In(3+).

Semiconductor quantum dots (QDs) with stable, oxidation resistant, and tunable photoluminescence (PL) are highly desired for various applications including solid-state lighting and biological labeling. However, many current systems for visible light emission involve the use of toxic Cd. Here, we report the synthesis and characterization of a series of codoped core/shell ZnSe/ZnS QDs with tunable PL maxima spanning 430-570 nm (average full width at half-maximum of 80 nm) and broad emission extending to 700 nm, through the use of Cu(+) as the primary dopant and trivalent cations (Al(3+), Ga(3+), and In(3+)) as codopants. Furthermore, we developed a unique thiol-based bidentate ligand that significantly improved PL intensity, long-term stability, and resilience to postsynthetic processing. Through comprehensive experimental and computational studies based on steady-state and time-resolved spectroscopy, electron microscopy, and density functional theory (DFT), we show that the tunable PL of this system is the result of energy level modification to donor and/or acceptor recombination pathways. By incorporating these findings with local structure information obtained from extended X-ray absorption fine structure (EXAFS) studies, we generate a complete energetic model accounting for the photophysical processes in these unique QDs. With the understanding of optical, structural, and electronic properties we gain in this study, this successful codoping strategy may be applied to other QD or related systems to tune the optical properties of semiconductors while maintaining low toxicity.