Bichalcogenophene Imide-Based Homopolymers: Chalcogen-Atom Effects on the Optoelectronic Property and Device Performance in Organic Thin-Film Transistors

Biselenophene Imide: Enabling Polymer Acceptor with High Electron Mobility for High-Performance All-Polymer Solar Cells

The shortage of narrow band gap polymer acceptors with high electron mobility is the major bottleneck for developing efficient all-polymer solar cells (all-PSCs). Herein, we synthesize a distannylated electron-deficient biselenophene imide monomer (BSeI-Tin) with high purity/reactivity, affording an excellent chance to access acceptor-acceptor (A-A) type polymer acceptors. Copolymerizing BSeI-Tin with dibrominated monomer Y5-Br, the resulting A-A polymer PY5-BSeI shows a higher molecular weight, narrower band gap, deeper-lying frontier molecular orbital levels and larger electron mobility than the donor-acceptor type counterpart PY5-BSe. Consequently, the PY5-BSeI-based all-PSCs deliver a remarkable efficiency of 17.77 % with a high short-circuit current of 24.93 mA cm-2 and fill factor of 75.83 %. This efficiency is much higher than that (10.70 %) of the PY5-BSe-based devices. Our study demonstrates that BSeI is a promising building block for constructing high-performance polymer acceptors and stannylation of electron-deficient building blocks offers an excellent approach to developing A-A type polymers for all-PSCs and even beyond.

Recent advances in n-type and ambipolar organic semiconductors and their multi-functional applications

Organic semiconductors have received broad attention and research interest due to their unique integration of semiconducting properties with structural tunability, intrinsic flexibiltiy and low cost. In order to meet the requirements of organic electronic devices and their integrated circuits, p-type, n-type and ambipolar organic semiconductors are all necessary. However, due to the limitation in both material synthesis and device fabrication, the development of n-type and ambipolar materials is quite behind that of p-type materials. Recent development in synthetic methods of organic semiconductors greatly enriches the range of n-type and ambipolar materials. Moreover, the newly developed materials with multiple functions also put forward multi-functional device applications, including some emerging research areas. In this review, we give a timely summary on these impressive advances in n-type and ambipolar organic semiconductors with a special focus on their synthesis methods and advanced materials with enhanced properties of charge carrier mobility, integration of high mobility and strong emission and thermoelectric properties. Finally, multi-functional device applications are further demonstrated as an example of these developed n-type and ambipolar materials.

Synthesis and Derivatization of an Isomerized Bithiophene Imide (iBTI) Acceptor with a Controllably Twisted Backbone

A heptagonal isomerized bithiophene imide (iBTI) acceptor has been effectively synthesized on a gram scale. Its series of β-, α',β-, α,α'-, α,α',β-, and α,α',β,β'-substituted derivatives can be obtained by controlling brominated sites. Single-crystal analyses indicate that the torsion angle of the imide backbone depends on the number and rigidity of β-substituted groups. Furthermore, the helical chirality of tetrasubstituted and [7]helicene-like derivatives based on iBTI shows great promise for the construction of chiral semiconductor materials.

n-Type Polymer Semiconductors Based on Dithienylpyrazinediimide

The development of n-type organic semiconductors critically relies on the design and synthesis of highly electron-deficient building blocks with good solubility and small steric hindrance. We report here a strongly electron-deficient dithienylpyrazinediimide (TPDI) and its n-type semiconducting polymers. The pyrazine substitution leads to the resulting polymers with much lower-lying lowest unoccupied molecular orbital (LUMO) levels and improved backbone planarity compared to the reported dithienylbenzodiimide (TBDI)- and fluorinated dithienylbenzodiimide (TFBDI)-based polymer analogues, thus yielding n-type transport character with an electron mobility up to 0.44 cm² V^-1 s^-1 in organic thin-film transistors. These results demonstrate that dithienylpyrazinediimide is a highly promising electron-deficient building block for constructing high-performance n-type polymers and the incorporation of pyrazine into imide-functionalized (hetero)arenes is an effective strategy to develop n-type polymers with deep-lying frontier molecular orbital (FMO) levels for organic optoelectronic devices.

Fusion of Aza- and Oxadiborepins with Furans in a Reversible Ring-Opening Process Furnishes Versatile Building Blocks for Extended π-Conjugated Materials

A modular synthesis of both difurooxa- and difuroazadiborepins from a common precursor is demonstrated. Starting from 2,2'-bifuran, after protection of the positions 5 and 5' with bulky silyl groups, formation of the novel polycycles proceeds through opening of the furan rings to a dialkyne and subsequent re-cyclization in the borylation step. The resulting bifuran-fused diborepins show pronounced stability, highly planar tricyclic structures, and intense blue light emission. Deprotection and transformation into dibrominated building blocks that can be incorporated into π-extended materials can be performed in one step. Detailed DFT calculations provide information about the aromaticity of the constituent rings of this polycycle.

Group 16 conjugated polymers based on furan, thiophene, selenophene, and tellurophene

Five-membered aromatic rings containing Group 16 elements (O, S, Se, and Te), also referred as chalcogenophenes, are ubiquitous building blocks for π-conjugated polymers (CPs). Among these, polythiophenes have been established as a model system to study the interplay between molecular structure, solid-state organization, and electronic performance. The judicious substitution of alternative heteroatoms into polythiophenes is a promising strategy for tuning their properties and improving the performance of derived organic electronic devices, thus leading to the recent abundance of CPs containing furan, selenophene, and tellurophene. In this review, we first discuss the current status of Kumada, Negishi, Murahashi, Suzuki-Miyaura, and direct arylation polymerizations, representing the best routes to access well-defined chalcogenophene-containing homopolymers and copolymers. The self-assembly, optical, solid-state, and electronic properties of these polymers and their influence on device performance are then summarized. In addition, we highlight post-polymerization modifications as effective methods to transform polychalcogenophene backbones or side chains in ways that are unobtainable by direct polymerization. Finally, the major challenges and future outlook in this field are presented.

Fused Bithiophene Imide Dimer-Based n-Type Polymers for High-Performance Organic Electrochemical Transistors

The development of n-type organic electrochemical transistors (OECTs) lags far behind their p-type counterparts. In order to address this dilemma, we report here two new fused bithiophene imide dimer (f-BTI2)-based n-type polymers with a branched methyl end-capped glycol side chain, which exhibit good solubility, low-lying LUMO energy levels, favorable polymer chain orientation, and efficient ion transport property, thus yielding a remarkable OECT electron mobility (μ_e ) of up to ≈10^-2  cm²  V^-1  s^-1 and volumetric capacitance (C*) as high as 443 F cm^-3 , simultaneously. As a result, the f-BTI2TEG-FT-based OECTs deliver a record-high maximum geometry-normalized transconductance of 4.60 S cm^-1 and a maximum μC* product of 15.2 F cm^-1  V^-1  s^-1 . The μC* figure of merit is more than one order of magnitude higher than that of the state-of-the-art n-type OECTs. The emergence of f-BTI2TEG-FT brings a new paradigm for developing high-performance n-type polymers for low-power OECT applications.

n-Type Organic and Polymeric Semiconductors Based on Bithiophene Imide Derivatives

ConspectusIn the last three decades, p-type (hole-transporting) organic and polymeric semiconductors have achieved great success in terms of materials diversity and device performance, while the development of n-type (electron-transporting) analogues greatly lags behind, which is limited by the scarcity of highly electron-deficient building blocks with compact geometry and good solubility. However, such n-type semiconductors are essential due to the existence of the p-n junction and a complementary metal oxide semiconductor (CMOS)-like circuit in organic electronic devices. Among various electron-deficient building blocks, imide-functionalized arenes, such as naphthalene diimide (NDI) and perylene diimide (PDI), have been proven to be the most promising ones for developing n-type organic and polymeric semiconductors. Nevertheless, phenyl-based NDI and PDI lead to sizable steric hindrance with neighboring (hetero)arenes and a high degree of backbone distortion in the resultant semiconductors, which greatly limits their microstructural ordering and charge transport. To attenuate the steric hindrance associated with NDI and PDI, a novel imide-functionalized heteroarene, bithiophene imide (BTI), was designed; however, the BTI-based semiconductors suffer from high-lying frontier molecular orbital (FMO) energy levels as a result of their electron-rich thiophene framework and monoimide group, which is detrimental to n-type performance.In this Account, we review a series of BTI derivatives developed via various strategies, including ring fusion, thiazole substitution, fluorination, cyanation, and chalcogen substitution, and elaborate the synthesis routes designed to overcome the synthesis challenges due to their high electron deficiency. After structural optimization, these BTI derivatives can not only retain the advantages of good solubility, a planar backbone, and small steric hindrance inherited from BTI but also have greatly suppressed FMO levels. These novel building blocks enable the construction of a great number of n-type organic and polymeric semiconductors, particularly acceptor-acceptor (or all-acceptor)-type polymers, with remarkable performance in various devices, including electron mobility (μ_e) of 3.71 cm² V^-1 s^-1 in organic thin-film transistors (OTFTs), a power conversion efficiency (PCE) of 15.2% in all-polymer solar cells (all-PSCs), a PCE of 20.8% in inverted perovskite solar cells (PVSCs), electrical conductivity (σ) of 0.34 S cm^-1 and a power factor (PF) of 1.52 μW m^-1 K^-2 in self-doped diradicals, and σ of 23.3 S cm^-1 and a PF of ∼10 μW m^-1 K^-2 in molecularly n-doped polymers, all of which are among the best values in each type of device. The structure-property-device performance correlations of these n-type semiconductors are elucidated. The design strategy and synthesis of these novel BTI derivatives provide important information for developing highly electron-deficient building blocks with optimized physicochemical properties. Finally, we offer our insights into the further development of BTI derivatives and semiconductors built from them.

Dithiophene-Fused Oxadiborepins and Azadiborepins: A New Class of Highly Fluorescent Heteroaromatics

Access to dithiophene-fused oxadiborepins and the first azadiborepins attained via a modular synthesis route are presented. The new compounds emit intense blue light, some of which demonstrate fluorescence quantum yields close to unity. Cyclic voltammetry (CV) revealed electrochemically reversible one-electron reduction processes. The weak aromatic character of the novel 1,2,7-azadiborepin ring is demonstrated with in-depth theoretical investigations using nucleus-independent chemical shift (NICS) scans and anisotropy of the induced current density (ACID) calculations.

Synthesis of benzo[b]chalcogenophenes fused to selenophenes via intramolecular electrophilic cyclization of 1,3-diynes

We describe herein an alternative and transition-metal-free procedure for the access of benzo[b]chalcogenophenes fused to selenophenes via intramolecular cyclization of 1,3-diynes. This efficient protocol involves a double cyclization of 1,3-diynyl chalcogen derivatives promoted by the electrophilic species of organoselenium generated in situ by the oxidative cleavage of the Se-Se bond of dibutyl diselenide using Oxone® in acetonitrile as solvent in an open-flask at 80 °C. In this study, 15 selenophenes with broad substrate scope were prepared in moderate to excellent yields (55-98%) with short reaction times (0.5-3.0 h).

Recent Advances in the Synthesis of Selenophenes and Their Derivatives

The selenophene derivatives are an important class of selenium-based heterocyclics. These compounds play an important role in prospecting new drugs, as well as in the development of new light-emitting materials. During the last years, several methods have been emerging to access the selenophene scaffold, employing a diversity of cyclization-based synthetic strategies, involving specific reaction partners and particularities. This review presents a comprehensive discussion on the recent advances in the synthesis of selenophene-based compounds, starting from different precursors, highlighting the main differences, the advantages, and limitations among them.

Naphthodithiophenediimide-Bithiopheneimide Copolymers for High-Performance n-Type Organic Thermoelectrics: Significant Impact of Backbone Orientation on Conductivity and Thermoelectric Performance

The development of n-type conjugated polymers with high electrical conductivity (σ) has continued to pose a massive challenge in organic thermoelectrics (OTEs). New structural insights into the charge-carrier transport are necessitated for the realization of high-performance OTEs. In this study, three new n-type copolymers, named pNB, pNB-Tz, and pNB-TzDP, consisting of naphthodithiophenediimide (NDTI) and bithiopheneimide (BTI) units, are synthesized by direct arylation polymerization. The backbone orientation is altered by incorporating thiazole units into the backbone and tuning the branching point of the side chain. The alteration of the backbone orientation from face-on to bimodal orientation with both face-on and edge-on fractions significantly impacts the σ and the power factors (PFs) of the polymers. As a result, pNB-TzDP, with the bimodal orientation, demonstrates a high σ of up to 11.6 S cm^-1 and PF of up to 53.4 µW m^-1 K^-2 , which are among the highest in solution-processed n-doped conjugated polymers reported so far. Further studies reveal that the bimodal orientation of pNB-TzDP introduces 3D conduction channels and leads to better accommodation of dopants, which should be the key factors for the excellent thermoelectric performance.

Narrow bandgap difluorobenzochalcogenadiazole-based polymers for high-performance organic thin-film transistors and polymer solar cells

A series of difluorobenzochalcogenadiazole-bithiophene copolymers are developed for high-performance organic semiconductors.