Papers by Elham Rezasoltani
arXiv (Cornell University), Nov 28, 2017
We report a neutral salt water based battery which uses p-type and n-type solution processed poly... more We report a neutral salt water based battery which uses p-type and n-type solution processed polymer films as the cathode and the anode of the cell. The specific capacity of the electrodes (approximately 30 mAh cm -3 ) is achieved via formation of bipolarons in both the p-type and n-type polymers. By engineering ethylene glycol and zwitterion based side chains attached to the polymer backbone we facilitate rapid ion transport through the non-porous polymer films. This, combined with efficient transport of electronic charge via the conjugated polymer backbones, allowed the films to maintain constant capacity at high charge and discharge rates (>1000 C-rate). The electrodes also show good stability during electrochemical cycling (less than 30% decrease in capacity over >1000 cycles) and an output voltage up to 1.4 V. The performance of these semiconducting polymers with polar side-chains demonstrates the potential of this material class for fast-charging, water based electrochemical energy storage devices. of toxicity and safety, although finding stable conjugated polymers with the very negative reduction potentials needed to maximize operational voltage in water remains a challenge. One perceived limitation of organic electrodes is their volumetric capacity which is controlled by the density of individual redox sites and their range of oxidation state which limits the achievable charge density under charging; this may be further compromised by the use of non-redox-active side chains for polymer processability and ionic access as well as by blending the polymer with additional conductive or insulating scaffolds. Approaches to electrochemical energy storage using conjugated molecular materials have included: the use of conjugated polymers to conduct charges to and from redox-active units, 20 conjugated polymers with pendant redox-active groups and non-conjugated polymers bearing either inchain or pendant redox-active groups, 22 including in some cases radical groups that are easily charged. Encouraging specific capacities of hundreds of mAh g -1 have been reported 14 for some systems along with high cycle-life but with limited charging and discharging rates. Polymer chain conjugation has been shown to enhance charging rates, apparently by facilitating electronic transport, 18 but only to around 100 C. Most reported systems operate in organic or acidic electrolytes and whilst some work with aqueous salt electrolytes they tend to require high salt concentrations. A primary challenge, therefore, appears to be achieving high ionic and electronic conductivity simultaneously, to enable the electrodes to charge and discharge efficiently in aqueous electrolytes. Here, we present a design strategy for conjugated polymer electrodes whereby we exploit side chain design to enhance ionic conductivity and separately optimize backbone and side-chain structures to enable mixed electronic-ionic conduction. First, we identify conjugated polymers with a low ionization potential, here referred to as p-type, or low reduction potential, here referred to as n-type, to address specifications for both cathode and anode materials with redox potentials which complement the allowed electrochemical window for water (in this context, 'p-type' and 'n-type' simply indicate their relative energetic 'ease' for oxidation and reduction, respectively, and not extrinsic doping). Secondly, we design polymer side chains based on ethylene glycol based structures (glycol) for the p-type and zwitterion structures for the n-type polymer. These side chains were chosen to favor conduction of alkali metal cations and halide anions, and to enable the use of neutral pH, sodium chloride water based electrolyte. A similar strategy was previously applied to the design of polymers for organic electrochemical transistors for bioelectronics, resulting in stable p-and n-type polymers with specific capacitances >350 F cm -3 using NaCl:deionized water (DIW) as electrolyte. The n-type polymer structures presented here illustrate the potential to further improve the specific capacity and application potential of these materials through side chain engineering. Charging and discharging of ~100 nm thick polymer films occurs efficiently on the second timescale. Our material design strategy addresses the three factors described above in that it enables efficient ion transport within the polymer films for fast charging/discharging; it results in p-type and n-type polymers with redox activity which takes advantage of nearly the full available electrochemical window of water; and it results in highly reversible electrochemical charging which is extended to the whole polymer film. We demonstrate battery devices combining the p-and n-type conjugated polymers as the cathode and the anode of a water based electrochemical storage cell that can be operated under a nearly unipolar potential window of 1.4 V at >1000 C-rate (i.e. using current values which charge/discharge the battery in 1/1000 hours). The device is a demonstration of a solution processable polymer battery working under neutral pH water conditions and showing rate capabilities comparable to supercapacitors.
Journal of Applied Physics, Aug 19, 2014
Chemistry of Materials, Sep 2, 2020
The performance of photovoltaic devices based on blends of conjugated polymers with non-fullerene... more The performance of photovoltaic devices based on blends of conjugated polymers with non-fullerene acceptors depends upon the phase behaviour and microstructure of the binary, which in turn depends on the chemical structures of the molecular components and the blend composition. We investigate the correlation between molecular structure, composition, phase behaviour and device performance of a model system comprising semi-crystalline poly-3-hexylthiophene (P3HT) as the donor polymer and three non-fullerene acceptors, two of which (O-IDTBR/EH-IDTBR) have a planar core with 1
Energy and Environmental Science, 2019
We report the development of redox-active conjugated polymers that have potential applications in... more We report the development of redox-active conjugated polymers that have potential applications in electrochemical energy storage. Side chain engineering enables processing of the polymer electrodes from solution, stability in aqueous electrolytes and efficient transport of ionic and electronic charge carriers. We synthesized a 3,3 0-dialkoxybithiophene homo-polymer (p-type polymer) with glycol side chains and prepared naphthalene-1,4,5,8-tetracarboxylic-diimide-dialkoxybithiophene (NDI-gT2) copolymers (n-type polymer) with either a glycol or zwitterionic side chain on the NDI unit. For the latter, we developed a post-functionalization synthesis to attach the polar zwitterion side chains to the polymer backbone to avoid challenges of purifying polar intermediates. We demonstrate fast and reversible charging of solution processed electrodes for both the p-and n-type polymers in aqueous electrolytes, without using additives or porous scaffolds and for films up to micrometers thick. We apply spectroelectrochemistry as an in operando technique to probe the state of charge of the electrodes. This reveals that thin films of the p-type polymer and zwitterion n-type polymer can be charged reversibly with up to two electronic charges per repeat unit (bipolaron formation). We combine thin films of these polymers in a two-electrode cell and demonstrate output voltages of up to 1.4 V with high redox-stability. Our findings demonstrate the potential of functionalizing conjugated polymers with appropriate polar side chains to improve the accessible capacity, and to improve reversibility and rate capabilities of polymer electrodes in aqueous electrolytes. Broader context The ideal electrode material for electrochemical energy storage should be able to transport both electrons and ions efficiently and store a large density of these charges at accessible potentials. In high-performance battery electrodes, the requirements of ionic and electronic conductivity and charge storage are commonly fulfilled by combining different materials to implement these functions separately. In this work we show that conjugated polymers can be designed to combine favourable ionic and electronic transport properties in a single-phase material through appropriate design of the polymer backbone and side chains. We find that whilst choice of polymer backbone controls stability, redox-potentials and electronic transport, design of the polar side chain influences the ionic mobility, charging rate capability and capacity. Using solution-processed p-and n-type polymers we demonstrate fast charging (on the second timescale) and reversible behaviour for microns-thick electrodes in aqueous electrolytes, and present a proof-of-concept energy storage device that functions in a saltwater electrolyte. In comparison with conventional lithium-ion electrodes, the new materials show fast charging rates without the need for additives or porous scaffolds, although with lower specific capacity. The new materials thus open up a new approach to the design of solution processable, non-toxic electrodes compatible with aqueous electrolytes.
Nature Communications, Jun 15, 2021
Spectroscopic measurements of charge transfer (CT) states provide valuable insight into the volta... more Spectroscopic measurements of charge transfer (CT) states provide valuable insight into the voltage losses in organic photovoltaics (OPVs). Correct interpretation of CT-state spectra depends on knowledge of the underlying broadening mechanisms, and the relative importance of molecular vibrational broadening and variations in the CT-state energy (static disorder). Here, we present a physical model, that obeys the principle of detailed balance between photon absorption and emission, of the impact of CT-state static disorder on voltage losses in OPVs. We demonstrate that neglect of CT-state disorder in the analysis of spectra may lead to incorrect estimation of voltage losses in OPV devices. We show, using measurements of polymer:non-fullerene blends of different composition, how our model can be used to infer variations in CT-state energy distribution that result from variations in film microstructure. This work highlights the potential impact of static disorder on the characteristics of disordered organic blend devices.
Département de Physique Faculté des arts et des sciences Thèse présentée à la Faculté des études ... more Département de Physique Faculté des arts et des sciences Thèse présentée à la Faculté des études supérieures en vue de l'obtention du grade de Philosophiae Doctor (Ph.D.) en Faculté des arts et des sciences
Proceedings of the nanoGe Fall Meeting 2019, Jul 16, 2019
12:30-12:45 Evidence for Charged Species Formation in High Persistence Length Organic Semiconduct... more 12:30-12:45 Evidence for Charged Species Formation in High Persistence Length Organic Semiconductors in Solution E. Rezasoltani,1 A. W. Parker,2 I. Sazanovich,2 M. Towrie,2 M. Bird,3 A. Virbule,1 M. S. Vezie,1 J. Nelson,1 S. C. Hayes4 1 Physics Dept., Imperial College London, London, UK, 2 Central Laser Facility, Research Complex at Harwell, STFC Rutherford Appleton Laboratory, UK, 3 Brookhaven National Laboratory, Upton, NY, USA, 4 Dept. of Chemistry, University of Cyprus, Nicosia, Cyprus
Journal of Materials Chemistry C, 2020
In this work, we designed and synthesized two novel perylene diimide (PDI) tetramers based on a t... more In this work, we designed and synthesized two novel perylene diimide (PDI) tetramers based on a tetrathienylethene core, named TTE-PDI4 and FTTE-PDI4, and investigated their application as nonfullerene acceptors for organic photovoltaics. The free rotation of PDIs and adjacent thiophene units renders TTE-PDI4 with a highly twisted molecular geometry. The ring fusion of TTE-PDI4 yields FTTE-PDI4, a more rigid molecule with increased intramolecular stacking. Interestingly, TTE-PDI4 and FTTE-PDI4 possess similar energy levels but very different UV-Vis absorptions, with the latter showing strong broad-band absorption with multiple sharp peaks in the 300-600 nm region. Through timedependent density functional theory (TD-DFT) calculations, we show that this broad absorption spectrum in FTTE-PDI4 arises from the combination of multiple bright transitions in the visible region with a strong vibronic progression, tentatively assigned to the dominant CQC stretching mode. TTE-PDI4, despite having a lower energy absorption onset, shows weaker absorption at long wavelengths. Due to its higher absorption as well as its increased rigidity, FTTE-PDI4 shows a higher photocurrent and hence a higher power conversion efficiency (PCE), of 6.6%, when blended with the polymer donor PFBDB-T than TTE-PDI4 based blends (PCE of 3.8%). The greater rigidity of FTTE-PDI4 is likely to contribute to the good fill factor of the blend devices. Potential for further improvement through reducing voltage losses is identified.
arXiv (Cornell University), Nov 28, 2017
We report a neutral salt water based battery which uses p-type and n-type solution processed poly... more We report a neutral salt water based battery which uses p-type and n-type solution processed polymer films as the cathode and the anode of the cell. The specific capacity of the electrodes (approximately 30 mAh cm-3) is achieved via formation of bipolarons in both the p-type and n-type polymers. By engineering ethylene glycol and zwitterion based side chains attached to the polymer backbone we facilitate rapid ion transport through the non-porous polymer films. This, combined with efficient transport of electronic charge via the conjugated polymer backbones, allowed the films to maintain constant capacity at high charge and discharge rates (>1000 Crate). The electrodes also show good stability during electrochemical cycling (less than 30% decrease in capacity over >1000 cycles) and an output voltage up to 1.4 V. The performance of these semiconducting polymers with polar side-chains demonstrates the potential of this material class for fast-charging, water based electrochemical energy storage devices.
Energy & Environmental Science
We combine experiments with density functional theory calculations, statistical analysis, and mac... more We combine experiments with density functional theory calculations, statistical analysis, and machine-learning to reveal the structure–absorption strength relationship and predict the absorption strength of organic non-fullerene acceptors.
Proceedings of the nanoGe Spring Meeting 2022, 2022
Nature Communications, 2021
Spectroscopic measurements of charge transfer (CT) states provide valuable insight into the volta... more Spectroscopic measurements of charge transfer (CT) states provide valuable insight into the voltage losses in organic photovoltaics (OPVs). Correct interpretation of CT-state spectra depends on knowledge of the underlying broadening mechanisms, and the relative importance of molecular vibrational broadening and variations in the CT-state energy (static disorder). Here, we present a physical model, that obeys the principle of detailed balance between photon absorption and emission, of the impact of CT-state static disorder on voltage losses in OPVs. We demonstrate that neglect of CT-state disorder in the analysis of spectra may lead to incorrect estimation of voltage losses in OPV devices. We show, using measurements of polymer:non-fullerene blends of different composition, how our model can be used to infer variations in CT-state energy distribution that result from variations in film microstructure. This work highlights the potential impact of static disorder on the characteristics...
Département de Physique Faculté des arts et des sciences Thèse présentée à la Faculté des études ... more Département de Physique Faculté des arts et des sciences Thèse présentée à la Faculté des études supérieures en vue de l'obtention du grade de Philosophiae Doctor (Ph.D.) en Faculté des arts et des sciences
Journal of Materials Chemistry C, 2020
Two PDI tetramers with a central tetrathienylethene core were investigated as non-fullerene accep... more Two PDI tetramers with a central tetrathienylethene core were investigated as non-fullerene acceptors in organic photovoltaics and the dramatic differences in their optical absorption spectra were rationalised on the basis of DFT calculations.
Advanced Energy Materials, 2020
The temperature dependent aggregation behavior of PffBT4T polymers used in organic solar cells pl... more The temperature dependent aggregation behavior of PffBT4T polymers used in organic solar cells plays a critical role in the formation of a favorable morphology in fullerene-based devices. However, there has been little investigation into the impact of donor/acceptor ratio on morphology tuning, especially for non-fullerene acceptors (NFAs). Herein, the influence of composition on morphology is reported for blends of PffBT4T-2DT with two NFAs, O-IDTBR and O-IDFBR. The monotectic phase behavior inferred from differential scanning calorimetry provides qualitative insight into the interplay between solid-liquid and liquidliquid demixing. Transient absorption spectroscopy suggests that geminate recombination dominates charge decay and that the decay rate is insensitive to composition, corroborated by negligible changes in open-circuit voltage. Exciton lifetimes are also insensitive to composition, which is attributed to the signal being dominated by acceptor excitons which are formed and decay in domains of similar size and purity irrespective of composition. A 2 hierarchical morphology is observed, where the composition dependence of size scales and scattering intensity from resonant soft X-ray scattering (R-SoXS) is dominated by variations in volume fractions of polymer/polymer rich domains. Results suggest an optimal morphology where polymer crystallite size and connectivity are balanced, ensuring a high probability of hole extraction via such domains.
Proceedings of the nanoGe Fall Meeting 2019, 2019
Energy & Environmental Science, 2019
Solution processable p-type and n-type conjugated polymers with polar side chains enable fast cha... more Solution processable p-type and n-type conjugated polymers with polar side chains enable fast charging in aqueous electrolytes and 1.4 V cell voltage.
Proceedings of the 1st Interfaces in Organic and Hybrid Thin-Film Optoelectronics, 2019
12:30-12:45 Evidence for Charged Species Formation in High Persistence Length Organic Semiconduct... more 12:30-12:45 Evidence for Charged Species Formation in High Persistence Length Organic Semiconductors in Solution E. Rezasoltani,1 A. W. Parker,2 I. Sazanovich,2 M. Towrie,2 M. Bird,3 A. Virbule,1 M. S. Vezie,1 J. Nelson,1 S. C. Hayes4 1 Physics Dept., Imperial College London, London, UK, 2 Central Laser Facility, Research Complex at Harwell, STFC Rutherford Appleton Laboratory, UK, 3 Brookhaven National Laboratory, Upton, NY, USA, 4 Dept. of Chemistry, University of Cyprus, Nicosia, Cyprus
Journal of Polymer Science Part B: Polymer Physics, 2017
We investigate the influence of particle plasmons on exciton and charge generation and recombinat... more We investigate the influence of particle plasmons on exciton and charge generation and recombination processes in the blend of poly (9-(1-octylnonyl)-9H-carbazolebenzothiadiazole-4,7-diyl-2,5-thiophenediyl) (PCDTBT) and [6,6]-phenyl-C 70 butyric acid methyl ester (PC 70 BM). The particle plasmons are generated from gold nanoparticles, which are embedded into PCDTBT:PC 70 BM blend. For the blend with gold nanoparticles, we observe enhance light harvesting. Despite the enhanced light collection, we find that the quasi-steady-state charge generation has not been influenced by the particle plasmons. However, the generation and recombination of long-lived (sub-millisecond) polaron paris have been significantly enhanced: from untrapped state in the pristine blend to the trapped state in the gold nanoparticle-embedded blend. This result implies that the plasmon-influenced polarons are trapped at the broadband geminate polaron pair (GPP) state. This state acts as an intermediate state, which either leads to the formation of charge transfer excitons (CTXs) or free charge carriers. In our case, the particle plasmon-influenced polarons are trapped in the GPP state, which leads to the formation of CTXs. For this reason, we do not observe the enhanced charge generation in PCDTBT:PC 70 BM blend with particle plasmon resonance. Finally, we revealed that the long-lived polarons mainly resulted from the localization by particle plasmons. The macroscopic modification in the blend film made negligible contributions to this influence. V
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Papers by Elham Rezasoltani