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Dive into the research topics where Svante Hedström is active.

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Featured researches published by Svante Hedström.


Physical Chemistry Chemical Physics | 2014

Light-harvesting capabilities of low band gap donor–acceptor polymers

Svante Hedström; Patrik Henriksson; Ergang Wang; Mats R. Andersson; Petter Persson

A series of nine donor-acceptor polymers, including three new and six polymers from previous work, have been investigated experimentally and theoretically. The investigation focuses on narrow band gaps and strong absorptions of the polymers, where experimentally determined first peak absorption energies range from 1.8 to 2.3 eV, and peak absorption coefficients vary between 19-67 L g(-1) cm(-1). An overall assessment of each polymers light-harvesting capability is made, and related to the chemical structure. Oligomer calculations using density functional theory are extrapolated to obtain size-converged polymer properties, and found to reproduce the experimental absorption trends well. Accurate theoretical predictions of absorption energies to within 0.06 eV of experiments, and absorption strength to within 12%, are obtained through the introduction of an empirical correction scheme. The computational and experimental results provide insight for the design of polymers with efficient absorption, concerning the intrinsic properties of the constituent units and the use of bulky side-groups.


Nature Materials | 2017

Robust resistive memory devices using solution-processable metal-coordinated azo aromatics

Sreetosh Goswami; Adam J. Matula; Santi Prasad Rath; Svante Hedström; Surajit Saha; Meenakshi Annamalai; Debabrata Sengupta; Abhijeet Patra; Siddhartha Sankar Ghosh; Hariom Jani; Soumya Sarkar; M. Motapothula; Christian A. Nijhuis; Jens Martin; Sreebrata Goswami; Victor S. Batista; T. Venkatesan

Non-volatile memories will play a decisive role in the next generation of digital technology. Flash memories are currently the key player in the field, yet they fail to meet the commercial demands of scalability and endurance. Resistive memory devices, and in particular memories based on low-cost, solution-processable and chemically tunable organic materials, are promising alternatives explored by the industry. However, to date, they have been lacking the performance and mechanistic understanding required for commercial translation. Here we report a resistive memory device based on a spin-coated active layer of a transition-metal complex, which shows high reproducibility (∼350 devices), fast switching (≤30 ns), excellent endurance (∼1012 cycles), stability (>106 s) and scalability (down to ∼60 nm2). In situ Raman and ultraviolet-visible spectroscopy alongside spectroelectrochemistry and quantum chemical calculations demonstrate that the redox state of the ligands determines the switching states of the device whereas the counterions control the hysteresis. This insight may accelerate the technological deployment of organic resistive memories.


Applied Physics Letters | 2013

Conformation sensitive charge transport in conjugated polymers

L. Mattias Andersson; Svante Hedström; Petter Persson

Temperature dependent charge carrier mobility measurements using field effect transistors and density functional theory calculations are combined to show how the conformation dependent frontier orb ...


ACS Applied Materials & Interfaces | 2015

One-Step Synthesis of Precursor Oligomers for Organic Photovoltaics: A Comparative Study between Polymers and Small Molecules

Wei Li; Daojuan Wang; Suhao Wang; Wei Ma; Svante Hedström; David Ian James; Xiaofeng Xu; Petter Persson; Simone Fabiano; Magnus Berggren; Olle Inganäs; Fei Huang; Ergang Wang

Two series of oligomers TQ and rhodanine end-capped TQ-DR were synthesized using a facile one-step method. Their optical, electrical, and thermal properties and photovoltaic performances were systematically investigated and compared. The TQ series of oligomers were found to be amorphous, whereas the TQ-DR series are semicrystalline. For the TQ oligomers, the results obtained in solar cells show that as the chain length of the oligomers increases, an increase in power conversion efficiency (PCE) is obtained. However, when introducing 3-ethylrhodanine into the TQ oligomers as end groups, the PCE of the TQ-DR series of oligomers decreases as the chain length increases. Moreover, the TQ-DR series of oligomers give much higher performances compared to the original amorphous TQ series of oligomers owing to the improved extinction coefficient (ε) and crystallinity afforded by the rhodanine. In particular, the highly crystalline oligomer TQ5-DR, which has the shortest conjugation length shows a high hole mobility of 0.034 cm(2) V(-1) s(-1) and a high PCE of 3.14%, which is the highest efficiency out of all of the six oligomers. The structure-property correlations for all of the oligomers and the TQ1 polymer demonstrate that structural control of enhanced intermolecular interactions and crystallinity is a key for small molecules/oligomers to achieve high mobilities, which is an essential requirement for use in OPVs.


Physical Chemistry Chemical Physics | 2015

Rational design of D–A1–D–A2 conjugated polymers with superior spectral coverage

Svante Hedström; Qiang Tao; Ergang Wang; Petter Persson

The spectral coverage of a light-harvesting polymer largely determines the maximum achievable photocurrent in organic photovoltaics, and therefore constitutes a crucial parameter for improving their performance. The D-A1-D-A2 copolymer motif is a new and promising design strategy for extending the absorption range by incorporating two acceptor units with complementary photoresponses. The fundamental factors that promote an extended absorption are here determined for three prototype D-A1-D-A2 systems through a combination of experimental and computational methods. Systematic quantum chemical calculations are then used to reveal the intrinsic optical properties of ten further D-A1-D-A2 polymer candidates. These investigated polymers are all predicted to exhibit intense primary absorption peaks at 615-954 nm, corresponding to charge-transfer (CT) transitions to the stronger acceptor, as well as secondary absorption features at 444-647 nm that originate from CT transitions to the weaker acceptors. Realization of D-A1-D-A2 polymers with superior spectral coverage is thereby found to depend critically on the spatial and energetic separation between the two distinct acceptor LUMOs. Two promising D-A1-D-A2 copolymer candidates were finally selected for further theoretical and experimental study, and demonstrate superior light-harvesting properties in terms of significantly extended spectral coverage. This demonstrates great potential for enhanced light-harvesting in D-A1-D-A2 polymers via multiple absorption features compared to traditional D-A polymers.


RSC Advances | 2016

Ultrafast excited state dynamics of [Cr(CO) 4 (bpy)] : Revealing the relaxation between triplet charge-transfer states

Fei Ma; Martin Jarenmark; Svante Hedström; Petter Persson; Ebbe Nordlander; Arkady Yartsev

Ultrafast excited state dynamics of [Cr(CO)4(bpy)] upon metal-to-ligand charge-transfer (1MLCT) transition have been studied by pump-probe absorption spectroscopy in CH3CN, pyridine and CH2Cl2 solvents. Intersystem crossing (ISC) was found to be very fast (∼100 fs) and efficient, while the formation of the photoproduct with one axial CO dissociated is significantly less competitive, indicating a barrier along the dissociative coordinate. As a refinement of the previous dynamic model [I. R. Farrell, et al., J. Am. Chem. Soc., 1999, 121, 5296−5301], we show that a conventional downhill energy relaxation concept dominates the observed dynamics. Experimentally, we have identified the consecutive population of two triplet states as a result of triplet electronic relaxation convoluted with vibrational and solvent relaxation (the overall time is 2.7–6.9 ps depending on solvent), as well as the overall depopulation of the excited state through the lowest triplet state (57–84 ps). Adaptive excitation pulse shaping could not achieve optimization of the photoproduct quantum yield via re-distribution of only low-frequency vibrational modes during excitation, indicating that the two low-lying 1MLCT states, Cr(3d) → π*bpy and Cr(3d) → π*CO, are not coupled.


Molecular Physics | 2017

Defining donor and acceptor strength in conjugated copolymers

Svante Hedström; Ergang Wang; Petter Persson

ABSTRACT The progress in efficiency of organic photovoltaic devices is largely driven by the development of new donor–acceptor (D–A) copolymers. The number of possible D–A combinations escalates rapidly with the ever-increasing number of donor and acceptor units, and the design process often involves a trial-and-error approach. We here present a computationally efficient methodology for the prediction of optical and electronic properties of D–A copolymers based on density functional theory calculations of donor- and acceptor-only homopolymers. Ten donors and eight acceptors are studied, as well as all of their 80 D–A copolymer combinations, showing absorption energies of 1.3–2.3 eV, and absorption strengths varying by up to a factor of 2.5. Focus lies on exhibited trends in frontier orbital energies, optical band gaps, and absorption intensities, as well as their relation to the molecular structure. Based on the results, we define the concept of donor and acceptor strength, and calculate this quantity for all investigated units. The light-harvesting capabilities of the 80 D–A copolymers were also assessed. This gives a valuable theoretical guideline to the design of D–A copolymers with the potential to reduce the synthesis efforts in the development of new polymers. GRAPHICAL ABSTRACT


Journal of Chemical Theory and Computation | 2017

Electron Transfer Assisted by Vibronic Coupling from Multiple Modes

Subhajyoti Chaudhuri; Svante Hedström; Dalvin D. Méndez-Hernández; Heidi P. Hendrickson; Kenneth A. Jung; Junming Ho; Victor S. Batista

Understanding the effect of vibronic coupling on electron transfer (ET) rates is a challenge common to a wide range of applications, from electrochemical synthesis and catalysis to biochemical reactions and solar energy conversion. The Marcus-Jortner-Levich (MJL) theory offers a model of ET rates based on a simple analytic expression with a few adjustable parameters. However, the MJL equation in conjunction with density functional theory (DFT) has yet to be established as a predictive first-principles methodology. A framework is presented for calculating transfer rates modulated by molecular vibrations, that circumvents the steep computational cost which has previously necessitated approximations such as condensing the vibrational manifold into a single empirical frequency. Our DFT-MJL approach provides robust and accurate predictions of ET rates spanning over 4 orders of magnitude in the 106-1010 s-1 range. We evaluate the full MJL equation with a Monte Carlo sampling of the entire active space of thermally accessible vibrational modes, while using no empirical parameters. The contribution to the rate of individual modes is illustrated, providing insight into the interplay between vibrational degrees of freedom and changes in electronic state. The reported findings are valuable for understanding ET rates modulated by multiple vibrational modes, relevant to a broad range of systems within the chemical sciences.


Nature Materials | 2017

Corrigendum: Robust resistive memory devices using solution-processable metal-coordinated azo aromatics

Sreetosh Goswami; Adam J. Matula; Santi Prasad Rath; Svante Hedström; Surajit Saha; Meenakshi Annamalai; Debabrata Sengupta; Abhijeet Patra; Siddhartha Sankar Ghosh; Hariom Jani; Soumya Sarkar; M. Motapothula; Christian A. Nijhuis; Jens Martin; Sreebrata Goswami; Victor S. Batista; T. Venkatesan

This corrects the article DOI: 10.1038/nmat5009.


Macromolecules | 2015

D-A(1)-D-A(2) Copolymers with Extended Donor Segments for Efficient Polymer Solar Cells

Qiang Tao; Yuxin Xia; Xiaofeng Xu; Svante Hedström; Olof Bäcke; David Ian James; Petter Persson; Eva Olsson; Olle Inganäs; Lintao Hou; Weiguo Zhu; Ergang Wang

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Ergang Wang

Chalmers University of Technology

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David Ian James

Chalmers University of Technology

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Jens Martin

University of California

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Patrik Henriksson

Chalmers University of Technology

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