Mats Fahlman - Academia.edu (original) (raw)

Papers by Mats Fahlman

Applied Catalysis B-environmental, Oct 1, 2019

The presence of elemental vacancies in materials are inevitable according to statistical thermody... more The presence of elemental vacancies in materials are inevitable according to statistical thermodynamics, which will decide the chemical and physical properties of the investigated system. However, the controlled manipulation of vacancies for specific applications is a challenge. Here we report a facile method for creating large concentrations of S vacancies in the inert basal plane of MoS2 supported on semimetal CoMoP2. With a small applied potential, S atoms can be removed in the form of H2S due to the optimized free energy of formation. The existence of vacancies favors electron injection from the electrode to the active site by decreasing the contact resistance. As a consequence, the activity is increased by 221 % with the vacancy-rich MoS2 as electrocatalyst for hydrogen evolution reaction (HER). A small overpotential of 75 mV is needed to deliver a current density of 10 mA cm-2 , which is considered among the best values achieved for MoS2. It is envisaged that this work may provide a new strategy for utilizing the semimetal phase for structuring MoS2 into a multifunctional material.

Research Square (Research Square), Aug 4, 2023

Water-based conductive inks are vital for sustainable manufacturing and widespread adoption of or... more Water-based conductive inks are vital for sustainable manufacturing and widespread adoption of organic electronic devices. Traditional methods to produce waterborne conductive polymers involve modifying their backbone with hydrophilic side chains or using surfactants to form and stabilize aqueous nanoparticle dispersions. However, these chemical approaches are not always feasible and can lead to poor material/device performance. Here, we demonstrate that groundstate electron transfer (GSET) between donor and acceptor polymers allows the processing of water-insoluble polymers from aqueous solutions. This mutual electrical doping enables solid films with 10,000× higher electrical conductivities than pristine polymers, low work function, and excellent thermal/solvent stability. These waterborne conductive films have technological implications for realizing high-performance organic solar cells, with efficiency and stability superior to conventional metal oxide electron transport layers, and organic electrochemical neurons with biorealistic firing frequency. Our findings demonstrate that GSET offers a new avenue to develop water-based conductive inks for a wide range of potential applications in organic electronics.

Journal of Materials Research, May 1, 2003

The contact formed between aluminum and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic aci... more The contact formed between aluminum and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) (PEDOT-PSS) derivatives was studied using x-ray photoelectron spectroscopy. The aluminum/PEDOT-PSS contact contains an interfacial layer formed by chemical reactions between aluminum and mainly poly(styrenesulfonic acid) (PSSH). These chemical interactions were studied with the help of model systems (PSSH, benzenesulfonic acid, and sodium benzenesulfonate). The preferred reaction site of aluminum is the SO3− and SO3−H+ groups of the PSS chains, giving rise to C-S-Al(-O) and C-O-Al species. The resulting contact formed consists of an insulating aluminum/PSS layer and a thin region of partially dedoped PEDOT-PSS. There is significant aluminum diffusion into films of the highly conducting form of PEDOT-PSS that have substantially less PSS at the surface. Hence, no (thick) aluminum/PSS layer is formed in this case, though the PEDOT chains close to the aluminum contact will still be partially dedoped as for the aluminum/PEDOT-PSS case.

Solid State Ionics, Jan 15, 2007

Chemical degradation of conjugated polymers is one cause of material failures in polymer-based (o... more Chemical degradation of conjugated polymers is one cause of material failures in polymer-based (opto)electronic devices, but can also be used as a technique for subtractive patterning of polymer films. When a large anodic potential is applied to the conducting polymer blend poly(3,4ethylenedioxythiophene)-poly(4styrenesulfonate), PEDOT:PSS, an over-oxidation reaction occurs, altering its electrical conductivity. Here, we have studied the effect of pH on the electrochemical over-oxidation process of PEDOT in PEDOT:PSS. High pH is associated with a decrease of over-oxidation potential and an increase of resistivity in the resulting film. Vibrational spectroscopy and photoelectron spectroscopy measurements on over-oxidized PEDOT:PSS films indicate that the decrease in conductivity results from cleavage of the conjugation pathway accompanied by the formation of sulfone, carbonyl and carboxylic groups in the polymer chain.

Synthetic Metals, Mar 1, 2001

ABSTRACT Sandwich-style interfaces of Al/LiF/poly(9,9-dioctyl-fluorene) and Al/CsF/poly(9,9-dioct... more ABSTRACT Sandwich-style interfaces of Al/LiF/poly(9,9-dioctyl-fluorene) and Al/CsF/poly(9,9-dioctyl-fluorene) have been studied using X-ray and ultraviolet photoelectron spectroscopy. In the case of LiF-deposition on poly(9,9-dioctyl-fluorene) films, doping did not occur, nor did the LiF dissociate upon Al-deposition. No significant shifts in binding energy of the core levels, or any changes in the work function were detected. However, for the Al/LiF/poly(9,9-dioctyl-fluorene) interface, there was no degradation of the pi -electronic structure, unlike the case for Al deposited directly unto poly(9,9-dioctyl-fluorene). For the Al/CsF/poly(9,9-dioctyl-fluorene) interface, the CsF dissociated upon Al deposition, with the Cs likely n-doping the polymer at the interface. When deposited onto an Al surface, CsF also was found to dissociate at the interface but remaining in the CsF form away from the Al surface. Vacuum level alignment occurs for poly(9,9-dioctyl-fluorene) films spun onto 'metal' substrates. The hole-injection barrier in poly(9,9-dioctyl-fluorene)-based LEDs is hence determined by the difference between anode work function and the polymer ionization potential.

ACS Applied Materials & Interfaces, May 12, 2017

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Angewandte Chemie, Aug 13, 2019

Conductivity,carrier mobility,and asuitable Gibbs free energy are important criteria that determi... more Conductivity,carrier mobility,and asuitable Gibbs free energy are important criteria that determine the performance of catalysts for ah ydrogen evolution reaction (HER). However,itisachallenge to combine these factors into asingle compound. Herein, we discover as uperior electrocatalyst for aH ER in the recently identified Dirac nodal arc semimetal PtSn 4 .T he determined turnover frequency (TOF) for each active site of PtSn 4 is 1.54 H 2 s À1 at 100 mV.T his sets abenchmark for HER catalysis on Pt-based noble metals and earthabundant metal catalysts.W em ake use of the robust surface states of PtSn 4 as their electrons can be transferred to the adsorbed hydrogen atoms in the catalytic process more efficiently.I na ddition, PtSn 4 displays excellent chemical and electrochemical stabilities after long-term exposure in air and long-time HER stability tests.

Chemistry of Materials, Apr 14, 2009

Chemical polymerization of a 3,4-ethylenedioxythiophene derivative bearing a sulfonate group (EDO... more Chemical polymerization of a 3,4-ethylenedioxythiophene derivative bearing a sulfonate group (EDOT-S) is reported. The polymer, PEDOT-S, is fully water-soluble and has been produced by polymerizing EDOT-S in water, using Na 2 S 2 O 8 and a catalytic amount of FeCl 3. Elemental analysis and XPS measurements indicate that PEDOT-S is a material with a substantial degree of self-doping, but also contains free sulfate ions as charge-balancing counterions of the oxidized polymer. Apart from selfdoping PEDOT-S, the side chains enable full water solubility of the material; DLS studies show an average cluster size of only 2 nm. Importantly, the solvation properties of the PEDOT-S are reflected in spin-coated films, which show a surface roughness of 1.2 nm and good conductivity (12 S/cm) in ambient conditions. The electro-optical properties of this material are shown with cyclic voltammetry and spectroelectrochemical experiment reveals an electrochromic contrast (∼48% at λ max) 606 nm).

Organic Electronics, Feb 1, 2005

A set of polyaniline-and poly(3,4-ethylene dioxythiophene)-based materials were studied as hole i... more A set of polyaniline-and poly(3,4-ethylene dioxythiophene)-based materials were studied as hole injection layers in polymer light emitting devices. The choice of polymeric counterion/dopant poly(styrenesulfonic acid), and poly(acrylamido-2-methyl-1-propanesulfonic acid), and poly(acrylamide) blended with polyaniline/poly(acrylamido-2-methyl-1-propanesulfonic acid) was found to influence both work function and film morphology, which in turn affects device performance. The work functions of the polymer films spanned the range of over 1 eV and the surface region of the films were found to be low in conducting polymer content compared to the bulk. This was particularly the case of the polyaniline/poly(acrylamido-2-methyl-1-propanesulfonic acid) blended with poly(acrylamide) which showed device efficiency equal to that of the poly(3,4-ethylene dioxythiophene)-poly(styrenesulfonic acid) reference. The turn on voltage, however, was significantly larger, likely due to the insulating poly(acrylamide)-rich surface region of the polyaniline/poly(acrylamido-2-methyl-1-propanesulfonic acid)/poly(acrylamide) film. The polymer blend of polyaniline/ poly(styrenesulfonic acid) yielded the highest work function (5.5 ± 0.1 eV).

Conventional electronics based on silicon, germanium, or compounds of gallium require prohibitive... more Conventional electronics based on silicon, germanium, or compounds of gallium require prohibitively expensive investments. A state-of-the-art microprocessor fabrication facility can cost up to $15 billion while using environmentally hazardous processes. In that context, the discovery of solution-processable conducting (and semiconducting) polymers stirred up expectations of ubiquitous electronics because it enables the mass-production of devices using well established high-volume printing techniques.In essence, this thesis attempts to study the characteristics and applications of thin conducting polymer films ( 100 μm). First, thin-films of organic materials were combined with an electric double layer capacitor to decrease the operating voltage of organic field effect transistors. In addition, ionic current-rectifying diodes membranes were integrated inside electrochromic displays to increase the device’s bistability and obviate the need for an expensive addressing backplane.This wo...

Polyaniline-metal interfaces : Implications on corrosion protection of steel and aluminum alloys.

Advanced Functional Materials, 2020

Despite quick development of perovskite light‐emitting diodes (PeLEDs) during the past few years,... more Despite quick development of perovskite light‐emitting diodes (PeLEDs) during the past few years, the fundamental mechanisms on how ion migration affects device efficiency and stability remain unclear. Here, it is demonstrated that the dynamic redistribution of mobile ions in the emissive layer plays a key role in the performance of PeLEDs and can explain a range of abnormal behaviours commonly observed during the device measurement. The dynamic redistribution of mobile ions changes charge–carrier injection and leads to increased recombination current; at the same time, the ion redistribution also changes charge transport and results in decreased shunt resistance current. As a result, the PeLEDs show hysteresis in external quantum efficiencies (EQEs) and radiance, that is, higher EQEs and radiance during the reverse voltage scan than during the forward scan. In addition, the changes on charge injection and transport induced by the ion redistribution also well explain the rise of the...

Science Bulletin, 2021

n/aFunding Agencies|Knut and Alice Wallenberg Foundation (KAW) through a Wallenberg Scholar grant... more n/aFunding Agencies|Knut and Alice Wallenberg Foundation (KAW) through a Wallenberg Scholar grant</p

Advanced Materials Technologies, 2021

Fluorescent nanohybrids, based on π‐extended hydroxyoxophosphole ligands grafted onto ZnO nanopar... more Fluorescent nanohybrids, based on π‐extended hydroxyoxophosphole ligands grafted onto ZnO nanoparticles, are designed and studied. The restriction of the intramolecular motions of the organic fluorophore, through either aggregates’ formation in solution or processing into thin films, forms highly emissive materials due to a strong aggregation induced emission effect. Theoretical calculations and XPS analyses were performed to analyze the interactions between the organic and inorganic counterparts. Preliminary results on the use of these nanohybrids as solution‐processed emissive layers in organic light emitting diodes (OLEDs) illustrate their potential for lighting applications.

Nature Communications, 2021

Conducting polymers, such as the p-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)... more Conducting polymers, such as the p-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), have enabled the development of an array of opto- and bio-electronics devices. However, to make these technologies truly pervasive, stable and easily processable, n-doped conducting polymers are also needed. Despite major efforts, no n-type equivalents to the benchmark PEDOT:PSS exist to date. Here, we report on the development of poly(benzimidazobenzophenanthroline):poly(ethyleneimine) (BBL:PEI) as an ethanol-based n-type conductive ink. BBL:PEI thin films yield an n-type electrical conductivity reaching 8 S cm−1, along with excellent thermal, ambient, and solvent stability. This printable n-type mixed ion-electron conductor has several technological implications for realizing high-performance organic electronic devices, as demonstrated for organic thermoelectric generators with record high power output and n-type organic electrochemical transistors with a unique depletion...

Nature Communications, 2020

Although perovskite light-emitting diodes (PeLEDs) have recently experienced significant progress... more Although perovskite light-emitting diodes (PeLEDs) have recently experienced significant progress, there are only scattered reports of PeLEDs with both high efficiency and long operational stability, calling for additional strategies to address this challenge. Here, we develop perovskite-molecule composite thin films for efficient and stable PeLEDs. The perovskite-molecule composite thin films consist of in-situ formed high-quality perovskite nanocrystals embedded in the electron-transport molecular matrix, which controls nucleation process of perovskites, leading to PeLEDs with a peak external quantum efficiency of 17.3% and half-lifetime of approximately 100 h. In addition, we find that the device degradation mechanism at high driving voltages is different from that at low driving voltages. This work provides an effective strategy and deep understanding for achieving efficient and stable PeLEDs from both material and device perspectives.