Conducting polymers are being considered promising candidates for sustainable organic batteries mainly due to their fast electron transport properties and high recyclability. In this work, key properties of polythiophene and polypyridine have been assessed through a combined theoretical and experimental study focusing on such applications. A theoretical protocol has been developed to calculate redox potentials in solution within the framework of the density functional theory and using continuous solvation models. Here, the evolution of the electrochemical properties of solvated oligomers as a function of the length of the chain is analyzed and then the polymer properties are estimated via linear regressions using ordinary least square. The predicted values were verified against our electrochemical experiments. This protocol can now be employed to screen a large database of compounds in order to identify organic electrodes with superior properties.
Organic compounds evolve as a promising alternative to the currently used inorganic materials in rechargeable batteries due to their low-cost, environmentally friendliness and flexibility. One of the strategies to reach acceptable energy densities and to deal with the high solubility of known organic compounds is to combine small redox active molecules, acting as capacity carrying centres, with conducting polymers. Following this strategy, it is important to achieve redox matching between the chosen molecule and the polymer backbone. Here, a synergetic approach combining theory and experiment has been employed to investigate this strategy. The framework of density functional theory connected with the reaction field method has been applied to predict the formal potential of 137 molecules and identify promising candidates for the referent application. The effects of including different ring types, e.g. fused rings or bonded rings, heteroatoms, [small pi] bonds, as well as carboxyl groups on the formal potential, has been rationalized. Finally, we have identified a number of molecules with acceptable theoretical capacities that show redox matching with thiophene-based conducting polymers which, hence, are suggested as pendent groups for the development of conducting redox polymer based electrode materials.
Terephthalate-substituted thiophene derivatives are promising redox-active components for anode materials in lithium-ion batteries. In this study, we present the synthesis of substituted 2-(thiophen-3-yl)terephthalate derivatives (TTDs) as suitable monomers for thiophene-based conducting redox polymers, along with their characterization by electrochemical and spectroscopic techniques. Density functional theory (DFT) calculations, utilizing the universal solvation model based on solute electron density (SMD), were used to predict both the first and the second reduction potentials of these TTDs. The computational results showed good agreement with the experimental data in nonaqueous acetonitrile solvent, with mean absolute errors of 30 and 40 mV for the first and second reduction steps, respectively. Time-dependent (TD) DFT calculations on TTDs indicated terephthalate local transitions at both 200 and 240 nm and charge-transfer transitions above 300 nm by examination of the involved molecular orbitals.
A new versatile polythiophene building block, 3-(3,4-ethylenedioxythiophene)prop-1-yne (pyEDOT) (3), is prepared from glycidol in four steps in 28% overall yield. pyEDOT features an ethynyl group on its ethylenedioxy bridge, allowing further functionalization by alkyne chemistry. Its usefulness is demonstrated by a series of functionalized polythiophene derivatives that were obtained by pre- and post-electropolymerization transformations, provided by the synthetic ease of the Sonogashira coupling and click chemistry.
Organic matter based battery materials have attracted large interest due to their inherent ability to provide an environmentally benign alternative to inorganic batteries because such materials can be produced from renewable resources via eco-efficient processes. The development of organic battery materials rely on several key factors that need to be resolved, the most important being dissolution problems, limited electronic conductivity, degradation of active material and slow redox kinetics. Conducting polymers are insoluble in most electrolytes, they are electronically conducting and show fast redox conversion but are, to some extent, unstable and have insufficient charge capacities for battery applications.
To understand the instability of conducting polymers we have measured self discharge rates in polypyrrole at different temperatures. From these experiments it is clear that the self-discharge originates from an activated redox reaction with an activation barrier of around 0.4 eV. Although the exact nature of the redox reaction has not been identified we have been able to link the self discharge to, what is commonly referred to as, over-oxidation. Over-oxidation is common to polyacetylene, polyparaphenylene, polypyrrole and polythiophene and this mechanism of self discharge is thus a general feature of conducting polymers. This self-discharge mechanism is suppressed by low polymer doping levels, low potentials and low temperatures.
By attaching high capacity redox active groups onto the conducting polymer backbone the charge capacity can be increased while retaining electronic conductivity and insolubility. We have attached quinone groups to each repeat unit of polypyrrole for this purpose. Interestingly, in-situ spectroscopic measurements show that during quinone redox conversion the polymer doping level is in-fact reduced. Since the doping level of the polymer affects the rate of self-discharge the attachment of quinone units to the polypyrrole chain not only increases the charge capacity but also provides a conceptual strategy to control self discharge.
In this report we present the synthesis and characterization of two conducting redox polymers (CRPs) with polythiophene backbone and diethyl terephthalate pendant groups for the use as anode materials in secondary batteries. The materials show excellent rate capability allowing 301,Lm layers to be fully converted within seconds without the use of conductive additives. The high rate capability is traced to the open morphology of the materials that allows for fast ion transport, and to the mediation of electrons through the conducting polymer (CP) backbone. The requirements for the latter are i) that the redox chemistry of the pendant groups and the CP backbone overlaps and ii) that the CP conductivity is not compromised by the presence of the pendant groups. In the CRPs presented herein both these requirements are met and this is thus the first report on successful combination of the redox chemistry of organic redox molecules with the n-doping of conducting polymers.
The combination of small, high charge capacity molecules as pendant groups with a conducting polymer backbone having good electronic conductivity upon doping, gives the possibility to design a high capacity conducting redox polymer material for electric energy storage applications. The desired synergetic effect of the two components requires energy matching as well as chemical compatibility of the pendant group and the polymer backbone. Here we investigate the matching of diethyl terephthalate (DeT) with the thiophene-based conducting polymers polythiophene (PT), poly(3,4-ethylenedioxythiophene) (PEDOT), and polyphenylthiophene. We show that a stable and well-defined electrochemical response of DeT is achieved, together with all conducting polymers except for PT in tetrabutylammonium hexafluorophosphate electrolyte, indicating good energy match as well as chemical compatibility between DeT and polymers. By varying the size of ammonium cations in the electrolytes, we further show how this size affects the conductivity and the cycling stability of the polymers and also that the n-doping performance of all conducting polymers can be improved by the use of smaller alkyl ammonium cations. On the basis of these results, we suggest that PEDOT and PT are suitable candidates for a polymer backbone in conducting redox polymers with DeT pendant groups.
Abstract The combination of high capacity redox active pendent groups and conducting polymers, realized in conducting redox polymers (CRPs), provides materials with high charge storage capacity that are electronically conducting which makes CRPs attractive for electrical energy storage applications. In this report, six polythiophene and poly(3,4-ethylenedioxythiophene)(PEDOT)-based CRPs with a diethyl terephthalate unit covalently bound to the polymer chain by various linkers have been synthesized and characterized electrochemically. The effects of the choice of polymer backbone and of the nature of the link on the electrochemistry, and in particular the cycling stability of these polymers, are discussed. All CRPs show both the doping of the polymer backbone as well as the redox behavior of the pendent groups and the redox potential of the pendent groups in the CRPs is close to that of corresponding monomer, indicating insignificant interaction between the pendant and the polymer backbone. While all CRPs show various degrees of charge decay upon electrochemical redox conversion, the PEDOT-based CRPs show significantly improved stability compared to the polythiophene counterparts. Moreover, we show that by the right choice of link the cycling stability of diethyl terephthalate substituted PEDOT-based CRPs can be significantly improved.
Non-activated charge transport has been demonstrated in terephthalate-functionalized conducting redox polymers. The transition from a temperature-activated conduction mechanism to a residual scattering mechanism was dependent on the doping level. The latter mechanism is associated with apparent negative activation barriers to charge transport and is generally found in polymer materials with a high degree of order. Crystallographic data, however, suggested a low degree of order in this polymer, indicating the existence of interconnected crystal domains in the predominantly amorphous polymer matrix through which the charge was transported. We have thus shown that the addition of bulky pendant groups to conducting polymers does not prevent efficient charge transport via the residual scattering mechanism with low barriers to charge transport.
Herein, polypyridine (P25Py) is for the first time evaluated as an anode material for organic matter based electric energy storage devices. P25Py is synthesized both chemically and electrochemically and the influence of electrolyte and solvent on the doping behavior of the material is investigated in propylene carbonate and acetonitrile with LiClO4 and TBAPF6. A battery consisting of P25Py coupled to a lithium metal disc is assembled and the electrochemical performance and cycling stability of the conjugated polymer is analyzed. In all electrolyte combinations P25Py is conductive and shows reversible redox chemistry between -1.0 and -2.0 V vs ferrocene with capacitive response characteristics. The electrochemical impedance spectroscopy response of the material can be described by a Randles equivalent circuit with a finite length Warburg diffusion element in which the diffusion coefficient of the cations increases with increasing doping level of the polymer. In the battery cell configuration the polymer shows reversible cycling with no capacity fading during the first 100 cycles without conducting additives. P25Py thus provides a promising alternative conducting polymer base for electrical energy storage applications which expands both the potential widow as well as the electrolyte compatibility of the flora of known conducting polymers.
A new conducting polymer poly (3, 4-phenylenedioxythiophene) is synthesized by the electrochemical polymerization technique with different solvents. We find that solvents used in electrochemical polymerization play important roles for the catalytic activity and morphology of the formed conducting polymers. The obtained poly (3, 4-phenylenedioxythiophene) is for the first time employed as counter electrode electrocatalyst in dye sensitized solar cells with cobalt-based electrolytes. We demonstrate that a polymer prepared from a mixed acetonitrile-dichloromethane solvent exhibit higher catalytic activity for redox reactions, as compared to that from a single solvent, dichloromethane. The devices based on this mixed solvent-based polymer from a mixed solvents show a high power conversion efficiency of 5.97%. An additional advantageous feature of the electrochemically polymerized poly (3, 4-phenylenedioxythiophene) for solar cell applications is the high transparency in the visible and nearinfrared region. We also investigate the beneficial effect of the poly (3, 4-phenylenedioxythiophene) layer thickness on device performance, and concluded that the series resistance and charge transfer resistance are greatly influenced by the thickness of polymer, as evidenced by electrochemical impedance spectroscopy measurements. The optimal thickness for poly (3, 4-phenylenedioxythiophene) is about 100 nm. Furthermore, the high catalytic activity and transparency of the new conducting polymer as counter electrode shows great promise for other optoelectronic applications.
This study presents new hole-transport materials (HTMs) to replace the central spiro linkage inspiro-OMeTAD by a CC bond in H11 and CC double bond in H12. This structural change results in a facile synthetic process and a significant change in the molecular geometry. EmployingH11 as HTM in combination with mixed ion perovskite [HC(NH2)2]0.85(CH3NH3)0.15Pb(I0.85Br0.15)3, gives a solar cell power conversion efficiency of 19.8%.
Perovskite solar cells, as an emergent technology for solar energy conversion, have attracted much attention in the solar cell community by demonstrating impressive enhancement in power conversion efficiencies. However, the high temperature and manually processed TiO2 underlayer prepared by spray pyrolysis significantly limit the large-scale application and device reproducibility of perovskite solar cells. In this study, lowtemperature atomic layer deposition (ALD) is used to prepare a compact Al2 O3 underlayer for perovskite solar cells. The thickness of the Al2 O3 layer can be controlled well by adjusting the deposition cycles during the ALD process. An optimal Al2 O3 layer effectively blocks electron recombination at the perovskite/fluorine-doped tin oxide interface and sufficiently transports electrons through tunneling. Perovskite solar cells fabricated with an Al2 O3 layer demonstrated a highest efficiency of 16.2 % for the sample with 50 ALD cycles (ca. 5 nm), which is a significant improvement over underlayer-free PSCs, which have a maximum efficiency of 11.0 %. Detailed characterization confirms that the thickness of the Al2 O3 underlayer significantly influences the charge transfer resistance and electron recombination processes in the devices. Furthermore, this work shows the feasibility of using a high band-gap semiconductor such as Al2 O3 as the underlayer in perovskite solar cells and opens up pathways to use ALD Al2 O3 underlayers for flexible solar cells.
Tremendous progress has recently been achieved in the field of perovskite solar cells (PSCs) as evidenced by impressive power conversion efficiencies (PCEs); but the high PCEs of >20% in PSCs has so far been mostly achieved by using the hole transport material (HTM) spiro-OMeTAD; however, the relatively low conductivity and high cost of spiro-OMeTAD significantly limit its potential use in large-scale applications. In this work, two new organic molecules with spiro[fluorene-9,9-xanthene] (SFX)-based pendant groups, X26 and X36, have been developed as HTMs. Both X26 and X36 present facile syntheses with high yields. It is found that the introduced SFX pendant groups in triphenylamine-based molecules show significant influence on the conductivity, energy levels, and thin-film surface morphology. The use of X26 as HTM in PSCs yields a remarkable PCE of 20.2%. In addition, the X26-based devices show impressive stability maintaining a high PCE of 18.8% after 5 months of aging in controlled (20%) humidity in the dark. We believe that X26 with high device PCEs of >20% and simple synthesis show a great promise for future application in PSCs, and that it represents a useful design platform for designing new charge transport materials for optoelectronic applications.