Nanostructured Conducting Polymers and Their Applications in Energy Storage Devices

Due to the energy requirements for various human activities, and the need for a substantial change in the energy matrix, it is important to research and design new materials that allow the availability of appropriate technologies. In this sense, together with proposals that advocate a reduction in the conversion, storage, and feeding of clean energies, such as fuel cells and electrochemical capacitors energy consumption, there is an approach that is based on the development of better applications for and batteries. An alternative to commonly used inorganic materials is conducting polymers (CP). Strategies based on the formation of composite materials and nanostructures allow outstanding performances in electrochemical energy storage devices such as those mentioned. Particularly, the nanostructuring of CP stands out because, in the last two decades, there has been an important evolution in the design of various types of nanostructures, with a strong focus on their synergistic combination with other types of materials. This bibliographic compilation reviews state of the art in this area, with a special focus on how nanostructured CP would contribute to the search for new materials for the development of energy storage devices, based mainly on the morphology they present and on their versatility to be combined with other materials, which allows notable improvements in aspects such as reduction in ionic diffusion trajectories and electronic transport, optimization of spaces for ion penetration, a greater number of electrochemically active sites and better stability in charge/discharge cycles.

Synthesis and photophysical properties of N-alkyl dithieno[3,2-b:2',3'-d]pyrrole based donor/acceptor-π-conjugated copolymers for solar-cell application

Two kinds of donor–acceptor π-conjugated copolymer based on poly{[N-hexyl-dithieno(3,2-b:2′,3′-d)pyrrole-2,6-diyl]alt-[isoindigo]} (PDTP-IID) and poly{[N-hexyl-dithieno(3,2-b:2′,3′-d)pyrrole-2,6-diyl]alt-[thiazol-2,5-diyl]} (PDTP-Thz) were investigated. These copolymers were synthesized via a Stille coupling reaction. The results showed the structure–property relationships of different donor–acceptor (D–A) combinations. The polymer structures and photophysical properties were characterized by ¹H NMR, TGA, DSC, UV-vis absorption spectroscopy, AFM, CV, and XRD measurement. Through UV-vis absorption and cyclic voltammetry (CV) measurements, it showed that the copolymers exhibit not only a low bandgap of 1.29 eV and 1.51 eV but also a deep highest occupied molecular orbital (HOMO) of −5.49 and −5.11 eV. Moreover, photovoltaic properties in combination with the fullerene derivatives were investigated. The device based on the copolymers with PC₇₁BM exhibited higher maximum power conversion efficiency and higher maximum short-circuit current density of 0.23% with 1.64 mA cm⁻² of PDTP-IID:PC₇₁BM and 0.13% with 1.11 mA cm⁻² of PDTP-Thz:PC₇₁BM than those of the copolymers with PC₆₁BM. Measurements performed for N-hexyl-dithieno(3,2-b:2′,3′-d)pyrrole-based copolymers proved the potential of these polymers to be applied in optoelectronic applications.

The relationships between the structure and the property of donor–acceptor copolymers based on dithieno[3,2-b:2′,3′-d]pyrrole as a strong donor unit and isoindigo or thiazole as acceptor units are successfully studied.

Significant Difference in Semiconducting Properties of Isomeric All-Acceptor Polymers Synthesized via Direct Arylation Polycondensation

The direct arylation polycondensation (DArP) appeared as an efficient method for producing semiconducting polymers but often requires acceptor monomers with orienting or activating groups for the reactive carbon-hydrogen (C-H) bonds, which limits the choice of acceptor units. In this study, we describe a DArP for producing high-molecular-weight all-acceptor polymers composed of the acceptor monomers without any orienting or activating groups via a modified method using Pd/Cu co-catalysts. We thus obtained two isomeric all-acceptor polymers, P1 and P2, which have the same backbone and side-chains but different positions of the nitrogen atoms in the thiazole units. This subtle change significantly influences their optoelectronic, molecular packing, and charge-transport properties. P2 with a greater backbone torsion has favorable edge-on orientations and a high electron mobility μ_e of 2.55 cm²  V^-1  s^-1 . Moreover, P2-based transistors show an excellent shelf-storage stability in air even after the storage for 1 month.

A newly designed anthracene and isoindigo based polymer: synthesis, electrochemical characterization and biosensor applications

A novel sensing platform based on a newly designed and synthesized polymer, poly[(E)-6-methyl-6′-(10-methylanthracen-9-yl)-1,1′-diundecyl-[3,3′-biindolinylidene]-2,2′-dione] (namely PIIDAnth), was fabricated and explored as a glucose amperometric biosensor.

Synthesis and photophysical characterization of isoindigo building blocks as molecular acceptors for organic photovoltaics

Five isoindigo-based donor-acceptor-donor (D-A-D) type small molecules have been synthesized in order to investigate their intramolecular charge transfer characteristics. UV-vis absorption of these dyes exhibits a wide absorption band ranging from 300 to 650 nm with two distinct bands, giving the narrow bandgaps between 1.72 and 1.85 eV. Taking into account their HOMO-LUMO energy levels and bandgaps, isoindigo dyes have been used in the active layer of organic solar cell (OSC) devices. When these small molecule semiconductors were used as acceptors with the donor poly(3-hexylthiophene-2,5-diyl (P3HT) polymer in the inverted OSC devices, the highest power conversion efficiency (PCE) was obtained as 0.10% for pyrene-substituted isoindigo derivative.

Dual-Catalytic Ag-Pd System for Direct Arylation Polymerization to Synthesize Poly(3-hexylthiophene)

Direct arylation polymerization (DArP) has gained interest in materials chemistry as a method to synthesize conjugated polymers with minimal use of harsh reagents and additional steps. Traditional DArP conditions do not readily yield ideal polymerization characteristics, including chain-growth and low dispersities. It would be of great utility to advance DArP methodology to become competitive with traditional conjugated polymerization techniques. We have developed conditions for a dual-catalytic Ag-Pd system for the synthesis of poly(3-hexylthiophene) (P3HT) that exhibits chain-growth kinetics, low dispersities, and catalyst chain association by Pd. Specifically, the presence of Ag-carboxylate additives plays a beneficial role in the polymerization as a C-H activating agent, while PEPPSI-iPr is used as the Pd source for C-C coupling. The addition of pyridine is necessary to inhibit Pd-mediated C-H activation in the interest of catalyst orthogonality, which can lower dispersities.

Synthesis of a 1,2-Dithienylethene-Containing Donor-Acceptor Polymer via Palladium-Catalyzed Direct Arylation Polymerization (DArP)

This paper reports the synthesis of D-A polymers containing 1,2-dithienylethene (DTE) units via palladium-catalyzed direct arylation polymerization (DArP). The reaction of dibromoisoindigo (1-Br) and DTE (2-H), in the presence of Pd₂(dba)₃·CHCl₃ (0.5 mol%), P(2-MeOC₆H₄)₃ (L1) (2 mol%), pivalic acid (1 equiv) as catalyst precursors, and Cs₂CO₃ (3 equiv) as a base affords poly(1-alt-2) with a high molecular weight (Mn up to 44,900). Although, it has been known that monomers, with plural C⁻H bonds, tend to form insoluble materials via direct arylation at undesirable C⁻H positions; the reaction of 1-Br and 2-H cleanly proceeds without insolubilization. The resulting polymer has a well-controlled structure and exhibits good charge transfer characteristics in an organic field-effect transistor (OFET), compared to the polymer produced by Migita⁻Kosugi⁻Stille cross-coupling polymerization. The DArP product displays an ideal linear relationship in the current⁻voltage curve, whereas the Migita⁻Kosugi⁻Stille product shows a VG-dependent change in the charge mobility.

3D-Printed OFETs of the 1,4-bis(3-phenylquinoxalin-2-yl)benzene-based polymer semiconductors

In this study, we polymerized a 1,4-bis(3-phenylquinoxalin-2-yl)benzene unit with DPP and isoindigo units to produce four new polymers and deeply investigated the influence of DPP and isoindigo units on the semiconductor characteristics, band gap, and orientation properties of these polymers.

Synthesis and organic field effect transistor properties of isoindigo/DPP-based polymers containing a thermolabile group

The effect of hydrogen bonding and π–π intermolecular stacking on the physical properties and device performance.

The optimization of donor-to-acceptor feed ratios with the aim of obtaining black-to-transmissive switching polymers based on isoindigo as the electron-deficient moiety

The polymers based on isoindigo, thiophene and ProDOT were synthesized and characterized. Black to transmissive polymers were obtained by controlling the feed ratios of the units.

C-H Arylation in the Synthesis of π-Conjugated Polymers

C-H activation reactions have allowed us to react traditionally chemically inert bonds in molecules to develop new methods for cross-coupling reactions. This type of reactivity can be applied to conjugated polymer materials in an effort to improve existing synthetic difficulties including harsh reaction conditions, multiple monomer functionalization steps, and organometallic reagent waste. In this Viewpoint, we highlight some of the encouraging advances in direct arylation polymerization (DArP) as well as ongoing challenges for future improvement and utility.

Poly(pentacyclic lactam-alt-diketopyrrolopyrrole) for field-effect transistors and polymer solar cells processed from non-chlorinated solvents

A highly crystalline conjugated polymer incorporating two electron-deficient units was applied in high performance organic field-effect transistors and polymer solar cells.

A conformational locking strategy in linked-acceptor type polymers for organic solar cells

The concept of introducing intramolecular noncovalent conformational locks into the polymer main chain was implemented to improve the coplanarity of the linked-acceptor polymers. As a result, the novel polymer shows the best power conversion efficiency of 8.18%.

Enhancing the photovoltaic performance of binary acceptor-based conjugated polymers incorporating methyl units

“Binary acceptors” conjugated polymers with methyl side units were found to provide high photocurrent and efficiency in solar cells due to the small crystal domain of polymers in blended thin films.

High Mobility Ambipolar Diketopyrrolopyrrole-Based Conjugated Polymer Synthesized Via Direct Arylation Polycondensation

A diketopyrrolopyrrole-based conjugated polymer, PDPP-4FTVT, which exhibits ambipolar transport behavior in air with hole and electron mobilities up to 3.40 and 5.86 cm(2) V(-1) s(-1), respectively, is synthesized via direct arylation polycondensation. Incorporation of F-atoms in β-positions of thiophene rings dramatically improves the efficiency of direct arylation polycondensation.

Linked-Acceptor Type Conjugated Polymer for High Performance Organic Photovoltaics with an Open-Circuit Voltage Exceeding 1 V

A linked-acceptor type conjugated polymer is designed and sythesized based on 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (BDTT) and linked-thieno[3,4-c]pyrrole-4,6-dione (LTPD). This polymer uses alkyl-substituted thiophene as a bridge. The PBDTT-LTPD includes two TPD units in one repeating unit, which can enhance acceptor density in the polymer backbone and lower the highest occupied molecular orbital (HOMO) level. By contrast, variable alkyl substitutions in the thiophene-bridges ensure the subtle regulation of polymer properties. The solar cells based on PBDTT-LTPD display an open-circuit voltage (Voc) that exceeds 1 V, and a maximum power conversion efficiency (PCE) of 7.59% is obtained. This PCE value is the highest for conventional single-junction bulk heterojunction solar cells with Voc values of up to 1 V. Given that PBDTT-LTPD exhibits a low HOMO energy level and a band gap equivalent to that of poly(3-hexylthiophene), PBDTT-LTPD/phenyl-C61-butyric acid methyl ester may be a promising candidate for the front cell in tandem polymer solar cells.

A high mobility DPP-based polymer obtained via direct (hetero)arylation polymerization

Many diketopyrrolopyrrole-based (DPP) polymers have shown remarkable transport properties and to fabricate cost efficient materials, the new direct (hetero)arylation polymerization (DHAP) could become a valuable tool.

A new thieno-isoindigo derivative-based D–A polymer with very low bandgap for high-performance ambipolar organic thin-film transistors

A new thieno-isoindigo derivative was synthesized by replacing the outer benzene ring of the isoindigo derivative (BIBDF) with thiophene.

Direct C–H arylation synthesis of (DD′AD′DA′)-constituted alternating polymers with low bandgaps and their photovoltaic performance

The alternating copolymers possess a planar backbone structure and high intramolecular charge transfer, and they contain a strong push–pull (D–A) system and gave a power conversion efficiency up to 2.36%.

Modulation of the properties of pyrrolo[3,4-c]pyrrole-1,4-dione based polymers containing 2,5-di(2-thienyl)pyrrole derivatives with different substitutions on the pyrrole unit

Properties of the pyrrole-based polymers were modulatedviathe insertion of different functional groups into the pyrrole unit.

Use of heteroaromatic spacers in isoindigo-benzothiadiazole polymers for ambipolar charge transport

Not only do we report two new polymers (PIIG-DTBT and PIIG-DSeBT) involving isoindigo and benzothiadiazole blocks constructed with thiophene and selenophene spacers, but also explore the optical, electrochemical, and charge-transport properties.

A narrow band gap isoindigo based molecular donor for solution processed organic solar cells

Organic photovoltaics devices with 3.2% PCE were demonstrated using an isoindigo small molecule donor: fullerene acceptor active layer.

25th anniversary article: isoindigo-based polymers and small molecules for bulk heterojunction solar cells and field effect transistors

Driven by the potential advantages and promising applications of organic solar cells, donor-acceptor (D-A) polymers have been intensively investigated in the past years. One of the strong electron-withdrawing groups that were widely used as acceptors for the construction of D-A polymers for applications in polymer solar cells and FETs is isoindigo. The isoindigo-based polymer solar cells have reached efficiencies up to ∼7% and hole mobilities as high as 3.62 cm(2) V(-1) s(-1) have been realized by FETs based on isoindigo polymers. Over one hundred isoindigo-based small molecules and polymers have been developed in only three years. This review is an attempt to summarize the structures and properties of the isoindigo-based polymers and small molecules that have been reported in the literature since their inception in 2010. Focus has been given only to the syntheses and device performances of those polymers and small molecules that were designed for use in solar cells and FETs. Attempt has been made to deduce structure-property relationships that would guide the design of isoindigo-based materials. It is expected that this review will present useful guidelines for the design of efficient isoindigo-based materials for applications in solar cells and FETs.

Preparation and Chemical Properties of π-Conjugated Polymers Containing Indigo Unit in the Main Chain

π-Conjugated polymers based on indigo unit were prepared. Dehalogenative polycondensation of N-hexyl-6,6′-dibromoindigo with a zerovalent nickel complex gave a homopolymer, P(HexI), in 77% yield. Copolymer of N-hexyl-indigo and pyridine, P(HexI-Py), was also prepared in 50% yield. P(HexI) showed good solubility in organic solvents, whereas P(HexI-Py) was only soluble in acids such as HCOOH. The weight-average molecular weights (M_w) of P(HexI) and P(HexI-Py) were determined to be 10,000 and 40,000, respectively, by a light scattering method. Pd-catalyzed polycondensation between 6,6′-dibromoindigo with N-BOC (BOC = t-butoxycarbonyl) substituents and a diboronic compound of 9,9-dioctylfluorene afforded the corresponding alternating copolymer, P(BOCI-Flu), as a deep red solid in 98% yield. P(BOCI-Flu) was soluble in N-methyl-2-pyrroridone and showed an M_w of 29,000 in GPC analysis. Treatment of P(BOCI-Flu) with CF₃COOH smoothly led to a BOC-deprotection reaction to give an insoluble deep green polymer, P(I-Flu), in a quantitative yield. Diffuse reflectance spectra of powdery P(BOCI-Flu) and P(I-Flu) showed peaks at about 580 nm and 630 nm, respectively, which are thought to originate from the indigo unit.

Acceptor-acceptor type isoindigo-based copolymers for high-performance n-channel field-effect transistors

Two acceptor-acceptor (A-A) type copolymers (PIIG-BT and PIIG-TPD) with backbones composed exclusively of electron-deficient units are designed and synthesized. Both copolymers show unipolar n-type operations. In particular, PIIG-BT shows electron mobility of up to 0.22 cm(2) V(-1) s(-1). This is a record value for n-type copolymers based on lactam cores.

Pd-catalyzed direct C–H arylation of thieno[3,4-c]pyrrole-4,6-dione (TPD): a step-economical synthetic alternative to access TPD-centred symmetrical small molecules

A viable synthetic alternative for the facile construction of various thieno[3,4-c]pyrrole-4,6-dione (TPD)-based π-functional small molecules through direct C–H arylations has been demonstrated.

Synthesis of donor–acceptor conjugated polymers based on benzo[1,2-b:4,5-b′]dithiophene and 2,1,3-benzothiadiazole via direct arylation polycondensation: towards efficient C–H activation in nonpolar solvents

1,2-Dimethylbenzene, as a nonpolar high boiling point solvent, has been discovered to be a superior medium to perform direct-arylation polymerization.

Recent developments on isoindigo-based conjugated polymers

A review of recent advances in isoindigo-based conjugated polymers for organic photovoltaic and field-effect transistor applications is presented.