Surface Trap Sites Research Articles

Improving the Device Stability by Controlling the Morphology of Quantum Dot Emissive Layer Via a Coating Process in Blue QLEDs

AbstractBlue light‐emitting CdSe@ZnS/ZnS quantum dot (QD) nanoparticles (NPs) were synthesized and their photophysical properties in both solution and film phases were investigated. The morphological properties of films prepared by different coating methods i. e. single layer coating from low to high concentrations of QD solutions and layer‐by‐layer (multilayer) coating within constant low QD solution concentration, were also examined in detail. Varying the concentration (1–10 mg/mL) and the number of layers (from 1–16) did not essentially affect the photophysical properties of QD films, although it resulted in a direct increment in QD film thickness. The concentration and layer‐dependent films were used as an emissive layer (EML) in QD light‐emitting diodes (QLEDs). Although the “6 mg/ml−1 Layer” QD EML‐based device exhibited relatively high device efficiency compared to the “1 mg/ml−10 Layers” based one at working voltage region, it had ~2‐fold higher efficiency roll‐off at high voltage region. The performance differences for both devices with the same QD EML thickness were attributed to the morphological variations for the QD layer in terms of surface roughness, void density, aggregates/clusters, and trap sites that were directly related to the charge injection balance and Auger recombination.

Third-order nonlinear optical properties of CsPbCl3 and CsPbBr3 perovskite quantum dots: Effects of particle size and surface traps

Particle size and surface trap effects on the third-order nonlinear optical (NLO) properties of CsPbCl3 and CsPbBr3 perovskite quantum dots (PQD) have been investigated using a femtosecond (fs) z-scan experiment. Firstly, optical, morphological, and structural characterizations of the synthesized PQDs were performed using linear absorption and photoluminescence (PL) spectra, XRD, and TEM methods. Next, NLO properties of CsPbCl3 and CsPbBr3 PQDs were studied at the operating wavelength of 800 nm and 3.564 × 1011 W/cm2 laser intensity. The nonlinear absorption coefficient (β), the nonlinear refraction coefficient (γ), and the third-order susceptibilities (χ(3)) values for both sample types were calculated to be on the order of 10−11 m/W, 10−17 m2/W, and 10−11 esu, respectively. The effects of particle size and surface trap sites on the nonlinear properties of the PQDs were studied thoroughly. γ, χ(3), and the unitless nonlinear figure of merits (FOM) parameters were realized to be proportional to the particle size for both types of materials. In addition, these parameters were improved by decreasing the surface trap sites in the PQDs. These results strongly indicate the significant potential of CsPbCl3 and CsPbBr3 PQDs for numerous nonlinear applications.

Highly effective Fe-doped TiO2 nanoparticles for removal of toxic organic dyes under visible light illumination

This article addresses the synthesis of Fe3+ doped TiO2 nanoparticles with variations of molar concentrations of Fe3+ and their adequate use as potential photocatalysts for Photocatalysis applications. Synthesized photocatalysts were characterized thoroughly by different analytical techniques in terms of morphological, chemical, structural, crystalline, optical, electronic structure, surface area etc properties. The occurrence of red shift phenomenon of the energy band gap attributes to the transfer of charges and transition between the d electrons of dopant and conduction band (CB) or valence band (VB) of TiO2. The doping of Fe3+ ions generates more trap sites for charge carriers with the surface trap sites. Thorough experimental conclusions revealed that the Fe3+ ions necessarily regulate the catalytic property of TiO2 nanomaterial. The obtained total degradation efficiency rate of Methylene Blue (MB) was 93.3% in the presence of 0.1 M Fe3+ in the host material and for Malachite Green Oxalate the efficiency was 100% in the presence of 0.05 M and 0.1 M Fe3+in the host material. In both the cases the total visible light irradiation time was 90 min. The adsorption properties of the photocatalysts have been also performed in a dark for 90 min in the presence of MB dye. However, till now there are hardly reported photocatalysts which shows complete degradation of these toxic organic dyes by visible light driven photocatalysis. of potential values of valence and conduction band shows the production of active oxidizing species for hydrogen yield and the possible mechanism of the Schottky barrier has been proposed. A schematic diagram of visible light driven Photocatalysis has been pictured showing degradation activity of Fe3+-TiO2 catalysts sample.

Acetylacetone‐TiO2 Promoted Large Area Compatible Cascade Electron Transport Bilayer for Efficient Perovskite Solar Cells

In designing efficient perovskite solar cells (PSCs), the selection of suitable electron transport layers (ETLs) is critical to the final device performance as they determine the driving force for selective charge extraction. SnO2 nanoparticles (NPs) based ETLs have been a popular choice for PSCs due to superior electron mobility, but their relatively deep‐lying conduction band energy levels (ECB) result in substantial potential loss. Meanwhile, TiO2 NPs establish favorable band alignment owing to shallower ECB, but their low intrinsic mobility and abundant surface trap sites impede the final performance. For this reason, constructing a cascaded bilayer ETL is highly desirable for efficient PSCs, as it can rearrange energy levels and exploit on advantages of an individual ETL. In this study, we prepare SnO2 NPs and acetylacetone‐modified TiO2 (Acac‐TiO2) NPs and implement them as bilayer SnO2/Acac‐TiO2 (BST) ETL, to assemble cascaded energy band structure. SnO2 contributes to rapid charge carrier transport from high electron mobility while Acac‐TiO2 minimizes band‐offset and effectively suppresses interfacial recombination. Accordingly, the optimized BST ETL generates synergistic influence and delivers power conversion efficiency (PCE) as high as 23.14% with open‐circuit voltage (VOC) reaching 1.14 V. Furthermore, the BST ETL is transferred to a large scale and the corresponding mini module demonstrates peak performance of 18.39% PCE from 25 cm2 aperture area. Finally, the BST‐based mini module exhibit excellent stability, maintaining 83.1% of its initial efficiency after 1000 h under simultaneous 1 Sun light‐soaking and damp heat (85 °C/RH 85%) environment.

Accelerating solid-liquid interfacial hole transfer kinetics through designed flower-like trivalent bismuth crystallite island for photoelectrochemical application

Hematite (Fe2O3) is an appealing photoanode material for photoelectrochemical application due to its suitable band-gap. However, the serious electron-hole recombination of hematite results in the photocurrent density generated is lower than the theoretical value. In this work, we loaded flower-like trivalent bismuth crystallite islands onto nano Fe2O3 electrodes to improve photoelectrochemical application. The trivalent bismuth ions decorated hematite photoanode demonstrates excellent photocurrent density, rapid water oxidation kinetics, and remarkable bulk separation efficiency. Mott-Schottky results indicate that surface-treated hematite showed increased carrier density and enhanced uptrend band bending. Furthermore, the trivalent bismuth ions accelerate hole capture through Bi(III)/Bi(V) exchange, reducing the recombination of oxygen-related holes with surface trapping sites. Under simulated sunlight irradiation, the photocurrent density at 1.23 (vs. RHE) exhibits fourfold enhancement that of hematite film. This work demonstrates a new possibility that Bi(III) compounds, in a passivation-like form, can effectively improve carrier transport on the surface of hematite photoanodes.

Perovskite zinc titanate-reduced graphene oxide nanocomposite photoanode for improved photovoltaic performance in dye-sensitized solar cell

The current generation of solar cells are playing a predominant role in energy storage industries due to their economic cost, abundant, and compact design for photovoltaic applications. In this context, composite materials based on perovskite zinc titanate nanoparticles (ZnTiO3 NPs) and perovskite zinc titanate-reduced graphene oxide nanocomposite (RGO-ZnTiO3 NC) were prepared by a simple sol-gel technique. The ZnTiO3 NPs and RGO-ZnTiO3 NC were subjected to X-ray diffraction analysis for calculating crystal structure, crystallite size, microstrain, and dislocation density. The band gap energy of the ZnTiO3 NPs and RGO-ZnTiO3 NCs was found to be 2.9 and 3.1 eV, respectively. X-ray photoelectron spectroscopy was used to determine elemental species of the RGO-ZnTiO3 NC. The photovoltaic performance of the dye-sensitized solar cell (DSSC) with RGO-ZnTiO3 NC photoanode exhibited strong dye adsorption to facilitate considerable light absorption and efficient electron transport, due to less surface trapping sites compared to unmodified ZnTiO3NPs photoanode based DSSC. The RGO-ZnTiO3 NC photoanode demonstrated best photovoltaic performance with a short-circuit current density of 4.27 mA cm−2 and better photoelectric conversion efficiency of 1.11%, which is ∼2.6 folds higher than the DSSC with ZnTiO3 NPs photoanode.

F- Serve as Surface Trapping Sites to Promote the Charge Separation and Transfer of TiO2.

Finding an effective strategy to promote the charge transfer and separation of TiO2 is urgently needed. Herein, a surface fluorination (F–)-modified TiO2 (denoted as TO-xF, where x represents the volume of HF added in the solution) catalyst has been prepared by a mild and facile post-treatment method. The changes induced by surface F– on the morphological, structural, and surface electronic features and the charge separation and transfer efficiency of TiO2 were specifically examined. Compared with pristine TO, TO-0.4F exhibits enhanced photocatalytic degradation of methyl orange and phenol, production of hydroxyl radicals, and photocurrent response. The enhanced photocatalytic activities of TO-0.4F can be attributed to the role of surface F– as surface trapping sites in effectively boosting the charge transfer and separation processes, which is verified by the steady-state and time-resolved fluorescence spectroscopy, electrochemical impedance spectroscopy, Bode plot, transient photocurrent response, and open-circuit voltage measurements. This study emphasizes the role of surface F– in promoting the charge transfer and separation and improving the photocatalytic activity of TiO2.

Inorganometallic Photocatalyst for CO2 Reduction.

ConspectusDuring the last few decades, the design of catalytic systems for CO2 reduction has been extensively researched and generally involves (1) traditional approaches using molecular organic/organometallic materials and heterogeneous inorganic semiconductors and (2) combinatory approaches wherein these materials are combined as needed. Recently, we have devised a number of new TiO2-mediated multicomponent hybrid systems that synergistically integrate the intrinsic merits of various materials, namely, molecular photosensitizers/catalysts and n-type TiO2 semiconductors, and lower the energetic and kinetic barriers between components. We have termed such multicomponent hybrid systems assembled from the hybridization of various organic/inorganic/organometallic units in a single platform inorganometallic photocatalysts. The multicomponent inorganometallic (MIOM) hybrid system onto which the photosensitizer and catalyst are coadsorbed efficiently eliminates the need for bulk-phase diffusion of the components and avoids the accumulation of radical intermediates that invokes a degradation pathway, in contrast to the homogeneous system, in which the free reactive species are concentrated in a confined reaction space. In particular, in energetic terms, we discovered that in nonaqueous media, the conduction band (CB) levels of reduced TiO2 (TiO2(e-)) are positioned at a higher level (in the range -1.5 to -1.9 V vs SCE). This energetic benefit of reduced TiO2 allows smooth electron transfer (ET) from injected electrons (TiO2(e-)) to the coadsorbed CO2 reduction catalyst, which requires relatively high reducing power (at least more than -1.1 V vs SCE). On the other hand, the existence of various shallow surface trapping sites and surface bands, which are 0.3-1.0 eV below the CB of TiO2, efficiently facilitates electron injection from any photosensitizer (including dyes having low excited energy levels) to TiO2 without energetic limitation. This is contrasted with most photocatalytic systems, wherein successive absorption of single high-energy photons is required to produce excited states with enough energy to fulfill photocatalytic reaction, which may allow unwanted side reactions during photocatalysis. In this Account, we present our recent research efforts toward advancing these MIOM hybrid systems for photochemical CO2 reduction and discuss their working mechanisms in detail. Basic ET processes within the MIOM system, including intervalence ET in organic/organometallic redox systems, metal-to-ligand charge transfer of organometallic complexes, and interfacial/outer-sphere charge transfer between components, were investigated by conducting serial photophysical and electrochemical analyses. Because such ET events occur primarily at the interface between the components, the efficiency of interfacial ET between the molecular components (organic/organometallic photosensitizers and molecular reduction catalysts) and the bulk inorganic solid (mainly n-type TiO2 semiconductors) has a significant influence on the overall photochemical reaction kinetics and mechanism. In some TiO2-mediated MIOM hybrids, the chemical attachment of organic or organometallic photosensitizing units onto TiO2 semiconductors efficiently eliminates the step of diffusion/collision-controlled ET between components and prevents the accumulation of reactive species (oxidatively quenched cations or reductively quenched anions) in the reaction solution, ensuring steady photosensitization over an extended reaction period. The site isolation of a single-site organometallic catalyst employing TiO2 immobilization promotes the monomeric catalytic pathway during the CO2 reduction process, resulting in enhanced product selectivity and catalytic performance, including lifetime extension. In addition, as an alternative inorganic solid scaffold, the introduction of a host porphyrin matrix (interlinked in a metal-organic framework (MOF) material) led to efficient and durable photocatalytic CO2 conversion by the new MOF-Re(I) hybrid as a result of efficient light harvesting/exciton migration in the porphyrinic MOF and rapid quenching of the photogenerated electrons by the doped Re(I) catalytic sites. Overall, the case studies presented herein provide valuable insights for the rational design of advanced multicomponent hybrid systems for artificial photosynthesis involving CO2 reduction.

Engineering interfacial charge transfer channel for efficient photocatalytic H2 evolution: The interplay of CoPx and Ca2+ dopant

Cobalt phosphide (CoPx) has been developed as a cost-effective cocatalyst for photocatalytic H2 evolution with the advantages of excellent conductivity, strong reduction ability, good thermal and chemical stability. In this work, a facile preparation strategy was proposed to fabricate ultrafine CoPx nanoparticles on the surface of CdS. The effective H2 production over ultrafine CoPx nanoparticles has been realized. In addition, we found Ca2+ as an alkaline earth metal ion can promote the interaction between CdS and CoPx. Both experimental results and density function theory indicate that the Ca2+ dopant can act as surface trapping sites on CdS and lead to efficient separation of photogenerated electron-hole pairs. The integration of CoPx and Ca2+ dopant can synergistically enhance both photogenerated electron-hole separation as well as interfacial charge transfer, which enables a remarkable improvement on the H2 generation performance of CdS. The photocatalytic H2 generation rate of Ca-modified CoPx@CdS can reach up to 2441.5 μmol h−1 under optimal conditions with the apparent quantum efficiency as high as 35.4% at 420 nm. This finding motivates the development of simplified fabrication procedures for constructing and modifying cobalt active sites with efficient photocatalytic H2 generation performance.

Surface Modification and Stabilization of Photoluminescence Perovskite Nanocrystals Via Atomic Layer Deposition

Photoluminescence perovskite nanocrystals (NCs) have shown significant potential in optoelectronic applications in view of their narrow band emission with high photoluminescence quantum yields (PLQYs) and color tunability. However, their poor stability in light, heat and water environments still hinders practical applications in optoelectronic and bioimaging fields due to their ionic character.Atomic layer deposition (ALD) has been developed as an attractive method to stabilize the crystal structure of perovskite NCs through encapsulation and surface passivation. In this presentation, several stabilization methods through ALD are introduced. First, a low-temperature Al2O3 ALD process was developed to enhance the stability of CsPbBr3 quantum dots-silica sphere in light, water and heat, which originated from the crystal structure stabilization after ALD coating. Nonetheless, a significant photoluminescence (PL) quenching of NCs was typically observed upon Al2O3 ALD. Accordingly, a specially designed ALD reactor integrated a FTIR spectrometer was exploited, which enabled in-situ characterizations to investigate ligands exchange and evolution during deposition after each precursor dosing. It was found that the surface chemical reaction between ALD precursor and capping oleic acid (OA) ligands led to reorganization of OA ligands that increased surface trap sites, leading to PL quenching. Based on the reaction mechanisms observed, a hybrid passivation strategy was developed to simultaneously enhance the photoluminescence quantum yield and the stability of perovskite NCs by two-step modification with surface halogen replenishment and ALD. Consequently, the PL quenching was avoided and the perovskite NCs/Al2O3 nanocomposites exhibited exceptional stability against water, light and heat. Our work provides a versatile method for preparing ultrastable perovskite NCs through ALD method and significantly improves their potential in LED illumination and backlight displays.

Anisotropic, Nonthermal Lattice Disordering Observed in Photoexcited PbS Quantum Dots

Given their nanoscale dimensions, colloidal semiconductor nanocrystals provide unique systems for investigating the dynamics controlling surface chemistry and fundamental issues regarding lattice reorganization upon changes in electron distribution. These systems are particularly amenable to ultrafast electron probes, offering an atomic level picture of the lattice reorganization involved following photoexcitation. Here, we study lead sulfide (PbS) quantum dots with ultrafast electron diffraction to characterize the atomic motions following high-intensity photoexcitation. Short-range nonthermal lattice distortions and increased atomic disorder were observed in PbS colloidal quantum dots ranging from 2.4 to 8.7 nm in size. These effects scaled inversely with size and were less pronounced in nanocrystals with a chloride-containing surface rather than only organic ligands, which is consistent with an effect arising at the surface. The anisotropic, nonthermal lattice disordering occurs preferentially along the (100) crystallographic directions, which could indicate an anisotropic distribution of localized charge between the differing lattice terminations of the {111} and {100} crystal facets. This is consistent with the larger anharmonicity for the lattice potential at lattice sites with reduced ligand coordination relative to the bulk, which has been shown to cause accelerated relaxation into dynamic and static surface trap sites. Through an exploration of quantum dot size and variation in surface termination, this work provides the missing structural details to advance our understanding and control of charge-carrier formation, trapping, and recombination processes in nanoscale semiconductor systems.

The Multiple Roles of Metal Ion Dopants in Spectrally Stable, Efficient Quasi‐2D Perovskite Sky‐Blue Light‐Emitting Devices

AbstractPerovskite light‐emitting devices (peLEDs) have recently gained widespread attention as candidates for next‐generation display technologies. Red and green peLEDs have achieved over 20% external quantum efficiency (EQE), however blue peLEDs still lag behind. One proposed solution for improving the performance of blue peLEDs has been doping the perovskite films with metal ions, ostensibly to passivate surface trap sites and improve the EQE. Despite a few recent reports, however, the many roles of the metal ion dopants have not yet been fully explored. Here improvements in the EQE and spectral stability of quasi‐2D perovskites, often called 2D/3D or layered perovskites are reported. CsPbBr3−xClx sky‐blue emitting peLEDs, with a maximum EQE of 7.5%, and color stable spectra at high applied voltages are achieved, via doping with divalent metal ions at concentrations of 0.5 to 10%, by mole ratio. After screening several candidates, two metal ions are identified, Mn2+ and Mg2+ that are particularly effective, as compared with PEA‐based quasi‐2D control devices. Then these examples are used to study the effect of metal ions more generally on the film morphology, the hole transport layer's conductivity, the trap density, and the energy funneling dynamics, all of which strongly influence the device performance.

Conformational and Compositional Tuning of Phenanthrocarbazole-Based Dopant-Free Hole-Transport Polymers Boosting the Performance of Perovskite Solar Cells.

Conjugated polymers are regarded as promising candidates for dopant-free hole-transport materials (HTMs) in efficient and stable perovskite solar cells (PSCs). Thus far, the vast majority of polymeric HTMs feature structurally complicated benzo[1,2-b:4,5-b’]dithiophene (BDT) analogs and electron-withdrawing heterocycles, forming a strong donor–acceptor (D–A) structure. Herein, a new class of phenanthrocarbazole (PC)-based polymeric HTMs (PC1, PC2, and PC3) has been synthesized by inserting a PC unit into a polymeric thiophene or selenophene chain with the aim of enhancing the π–π stacking of adjacent polymer chains and also to efficiently interact with the perovskite surface through the broad and planar conjugated backbone of the PC. Suitable energy levels, excellent thermostability, and humidity resistivity together with remarkable photoelectric properties are obtained via meticulously tuning the conformation and elemental composition of the polymers. As a result, PSCs containing PC3 as dopant-free HTM show a stabilized power conversion efficiency (PCE) of 20.8% and significantly enhanced longevity, rendering one of the best types of PSCs based on dopant-free HTMs. Subsequent experimental and theoretical studies reveal that the planar conformation of the polymers contributes to an ordered and face-on stacking of the polymer chains. Furthermore, introduction of the “Lewis soft” selenium atom can passivate surface trap sites of perovskite films by Pb–Se interaction and facilitate the interfacial charge separation significantly. This work reveals the guiding principles for rational design of dopant-free polymeric HTMs and also inspires rational exploration of small molecular HTMs.

The influence of orthophosphoric-acid surface modification on charge-storage enhancement in polypropylene electrets

Bipolar electrets from polypropylene (PP) are essential, e.g., in electret air filters and in cellular-foam ferroelectrets. Therefore, the mechanism of surface-charge stability enhancement on PP electrets via orthophosphoric-acid surface treatment is investigated in detail. It is shown that the significant charge-stability enhancement can be mainly attributed to deeper surface traps originating from deposited chemicals and topographic features on the modified surfaces. Thermally stimulated discharge of chemically treated and non-treated PP films with different surface-charge densities is used to test the limits of the newly formed deep traps in terms of the capacity for hosting surface charges. When the initial surface-charge density is very high, more charges are forced into shallower original traps on the surface or in the bulk of the treated PP samples, reducing the effect of the deeper surface traps brought by the surface modification. The well-known crossover phenomenon (of the surface-charge decay curves) has been observed between modified PP electrets charged to ±2 kV and to ±3 kV. Acoustically probed charge distributions in the thickness direction of PP electrets at different stages of thermal discharging indicate that the deep surface trapping sites may have preference for negative charges, resulting in the observed asymmetric charge stability of the modified PP films.

Fluorescence and Optical Activity of Chiral CdTe Quantum Dots in Their Interaction with Amino Acids.

Ligand-induced chirality in semiconducting nanocrystals has been the subject of extensive study in the past few years and shows potential applications in optics and biology. Yet, the origin of the chiroptical effect in semiconductor nanoparticles is still not fully understood. Here, we examine the effect of the interaction with amino acids on both the fluorescence and the optical activity of chiral semiconductor quantum dots (QDs). A significant fluorescence enhancement is observed for l/d-Cys-CdTe QDs upon interaction with all the tested amino acids, indicating suppression of nonradiative pathways as well as the passivation of surface trap sites brought via the interaction of the amino group with the CdTe QDs’ surface. Heterochiral amino acids are shown to weaken the circular dichroism (CD) signal, which may be attributed to a different binding configuration of cysteine molecules on the QDs’ surface. Furthermore, a red shift of both CD and fluorescence signals in l/d-Cys-CdTe QDs is only observed upon adding cysteine, while other tested amino acids do not exhibit such an effect. We speculate that the thiol group induces orbital hybridization of the highest occupied molecular orbital (HOMOs) of cysteine and the valence band of CdTe QDs, leading to the decrease of the energy band gap and a concomitant red shift of CD and fluorescence spectra. This is further verified by density functional theory calculations. Both the experimental and theoretical findings indicate that the addition of ligands that do not “directly” interact with the valence band (VB) of the QD (noncysteine moieties) changes the QD photophysical properties, as it probably modifies the way cysteine is bound to the surface. Hence, we conclude that it is not only the chemistry of the amino acid ligand that affects both CD and PL but also the exact geometry of binding that modifies these properties. Understanding the relationship between the QD’s surface and chiral amino acid thus provides an additional perspective on the fundamental origin of induced chiroptical effects in semiconductor nanoparticles, potentially enabling us to optimize the design of chiral semiconductor QDs for chiroptic applications.

Effect of Pelargonidin on carrier recombination lifetime of CTS quantum dots

In the current work, we have prepared stacks of Copper tin sulphide (CTS)/Pelargonidin core/shell quantum dots on soda lime substrates by SILAR technique. Copper tin sulphide quantum dots were of tetragonal phase matching well with JCPDS 089-4714. The absorption coefficient of the core/shell quantum dots increased while the photoluminescence intensity decreased with increasing shell thickness. Decrease of charge carrier confinement energy due to leakage of wavefunction into the shell is the cause of fall in PL intensity. Three transitions were found in all the samples corresponding to 1Se-1Sh, 1Pe-1Ph and 1De-1Dh transitions using the non-interacting particle model. Charge carrier recombination lifetime of P state was found to be in the order of 100 ns, with lifetime increasing with shell thickness, probably due to the P state being the most occupied at room temperature and decrease of surface trap sites with increasing shell thickness. Owing to the high lifetime of CTS/Pelargonidin core/shell quantum dots, these can be used effectively in solar cells where recombination time is a deciding factor for efficiency and also in bioimaging of living cells and tissues.

Polymeric, Cost-Effective, Dopant-Free Hole Transport Materials for Efficient and Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) has skyrocketed in the past decade to an unprecedented level due to their outstanding photoelectric properties and facile processability. However, the utilization of expensive hole transport materials (HTMs) and the inevitable instability instigated by the deliquescent dopants represent major concerns hindering further commercialization. Here, a series of low-cost, conjugated polymers are designed and applied as dopant-free HTMs in PSCs, featuring tuned energy levels, good temperature and humidity resistivity, and excellent photoelectric properties. Further studies highlight the critical and multifaceted roles of the polymers with respect to facilitating charge separation, passivating the surface trap sites of perovskite materials, and guaranteeing long-term stability of the devices. A stabilized power conversion efficiency (PCE) of 20.3% and remarkably enhanced device longevity are achieved using the dopant-free polymer P3 with a low concentration of 5 mg/mL, qualifying the device as one of the best PSC systems constructed on the basis of dopant-free HTMs so far. In addition, the flexible PSCs based on P3 also exhibit a PCE of 16.2%. This work demonstrates a promising route toward commercially viable, stable, and efficient PSCs.

Modeling SOx trapping on a copper-doped CuO/SBA-15 sorbent material

A mixture of SO2 and air was continuously injected in a fixed bed reactor containing a CuO/SBA-15 sorbent material and submitted to an isothermal temperature between 325 and 400 °C. The SO2 emissions were measured at the exit of the reactor. Different isothermal temperatures, different injected SO2 concentrations and different sorbent masses, all representative of industrial conditions, were tested. The purpose of the paper was to propose efficient global models which simulate the breakthrough curves whatever the experimental conditions. A simplified model was first considered assuming that the oxidation and trapping processes can occur on each copper site. The values of the four kinetic parameters which are involved were determined solving this model using Scilab software and an optimization routine. Because this model failed to reproduce in a satisfying way the breakthrough curves for different sorbent masses, a second model was introduced which involves surface and bulk trapping sites and six kinetic parameters. The breakthrough curves simulated with this second model following the same resolution techniques were in better agreement with the experimental ones, whatever the experimental conditions. For comparison, a simulation of the breakthrough curves returned by a model with bulk diffusion was presented.

Resonance-Frequency Modulation for Rapid, Point-of-Care Ebola-Glycoprotein Diagnosis with a Graphene-Based Field-Effect Biotransistor

Recent outbreaks of Ebola-virus infections in several countries demand a rapid point-of-care (POC) detection strategy. Here we report an innovative pathway founded on electronic-resonance-frequency modulation to detect Ebola glycoprotein (GP), on the basis of a carrier-injection-trapping-release-transfer mechanism and the standard antibody-antigen interaction principle within a dielectric-gated reduced graphene oxide (rGO) field-effect transistor (GFET). The sensitivity of Ebola detection can be significantly enhanced by monitoring the device’s electronic-resonance frequency, such as its inflection frequency, where the phase angle reaches a maximum. In addition to an excellent selectivity, a sensitivity of ~36-160 % and ~17-40 % for 0.001-3.401 mg/L Ebola GP can be achieved at high and low inflection resonance frequencies, respectively, which are several orders of magnitude higher than those from other electronic parameters (e.g., resistance-based sensitivity). Using equivalent circuit modeling for contributions from channel and contact, analytical equations for resonance shifts have been generalized. When matching with the incoming ac-measurement signal, electronic resonance from the phase-angle spectrum evolves from various relaxation processes (e.g., trap and release of injected charges at surface-trap sites of the channel-gate oxide and channel-source or drain interfaces) that are associated with a characteristic emission frequency. Using charge relaxation dynamics, a high-performance bio-FET sensing platform for healthcare is realized through resonance shifting. Figure 1

Resonance-Frequency Modulation for Rapid, Point-of-Care Ebola-Glycoprotein Diagnosis with a Graphene-Based Field-Effect Biotransistor.

Recent outbreaks of Ebola-virus infections in several countries demand a rapid point-of-care (POC)-detection strategy. This paper reports on an innovative pathway founded on electronic-resonance-frequency modulation to detect Ebola glycoprotein (GP), on the basis of a carrier-injection-trapping-release-transfer mechanism and the standard antibody-antigen-interaction principle within a dielectric-gated reduced graphene oxide (rGO) field-effect transistor (GFET). The sensitivity of Ebola detection can be significantly enhanced by monitoring the device's electronic-resonance frequency, such as its inflection frequency ( fi), where the phase angle reaches a maximum (θmax). In addition to excellent selectivity, a sensitivity of ∼36-160% and ∼17-40% for 0.001-3.401 mg/L Ebola GP can be achieved at high and low inflection-resonance frequencies, respectively, which are several orders of magnitude higher than the sensitivity from other electronic parameters (e.g., resistance-based sensitivity). Using equivalent circuit modeling for contributions from channel and contact, analytical equations for resonance shifts have been generalized. When matching with the incoming ac-measurement signal, electronic resonance from the phase-angle spectrum evolves from various relaxation processes (e.g., trap and release of injected charges at surface-trap sites of the channel-gate oxide and channel-source or drain interfaces) that are associated with a characteristic emission frequency. Using charge-relaxation dynamics, a high-performance bio-FET sensing platform for healthcare and bioelectronic applications is realized through resonance shifting.