Effect of Chalcogen Atom Substitution on the Optoelectronic Properties in Cyclopentadithiophene Polymers

Origin of Optoelectronic Contradictions in 3,4-Cycloalkyl[c]-chalcogenophenes: A Computational Study

The planar morphology of the backbone significantly contributes to the subtle optoelectronic features of π-conjugated polymers. On the other hand, the atomistic tuning of an otherwise identical π-backbone could also impact optoelectronic properties systematically. In this manuscript, we compare a series of 3,4-cycloalkylchalcogenophenes by tuning them atomistically using group-16 elements. Additionally, the effect of systematically extending these building blocks in the form of oligomers and polymers is studied. The size of the 3,4-substitution affected the morphology of the oligomers. In addition, the heteroatoms contributed to a further alteration in their geometry and resultant optoelectronic properties. The chalcogenophenes, containing smaller 3,4-cycloalkanes, resulted in lower bandgap oligomers or polymers compared to those with larger 3,4-cycloalkanes. Natural bonding orbital (NBO) calculations were performed to understand the disparity alongside the contour maps of frontier molecular orbitals (FMO).

Optical and electronic properties enhancement via chalcogenides: promising materials for DSSC applications

CONTEXT

Comparatively, metal-free sensitizers featuring the chalcogen family receive less attention despite known electronic properties for metal-chalcogenide materials. This work reports an array of optoelectronic properties using quantum chemical methods. Observed red-shifted bands within the UV/Vis to NIR regions with absorption maxima > 500 nm were consistent with increasing chalcogenide size. There is a monotonic down-shift in the LUMO and ESOP energy consistent with O 2p, S 3p, Se 4p, to Te 5p atomic orbital energies. Excited-state lifetime and charge injection free energies follow the decreasing order of chalcogenide electronegativity. Adsorption energies of dyes on TiO₂ anatase (101) range between - 0.08 and - 0.77 eV. Based on evaluated properties, selenium- and tellurium-based materials show potential use in DSSCs and futuristic device applications. Therefore, this work motivates continued investigation of the chalcogenide sensitizers and their application.

METHODS

The geometry optimization was performed at B3LYP/6-31 + G(d,p) and B3LYP/LANL2DZ level of theory for lighter and heavier atoms, respectively, using Gaussian 09. The equilibrium geometries were confirmed by the absence of imaginary frequencies. Electronic spectra were obtained at CAM-B3LYP/6-31G + (d,p)/LANL2DZ level of theory. Adsorption energies for dyes on a 4 × 5 supercell TiO₂ anatase (101) were obtained using VASP. The dye-TiO₂ optimizations were employed using GGA and PBE with the PAW pseudo-potentials. The energy cutoff was set at 400 eV and convergence threshold for self-consistent iteration was set to 10^-4, and van der Waals were accounted using DFT-D3 model and on-site Coulomb repulsion potential set at 8.5 eV for Ti.

Near-Infrared Emissive Hypervalent Compounds with Germanium(IV)-Fused Azobenzene π-Conjugated Systems

A novel molecular design for showing near-infrared (NIR) emission is still required for satisfying growing demands for NIR-light technology. In this research, hypervalent compounds with germanium (Ge)-fused azobenzene (GAz) scaffolds were discovered that can exhibit NIR emission (λ_PL =690∼721 nm, Φ_PL =0.03∼0.04) despite compact π-conjugated systems. The unique optical properties are derived from the trigonal bipyramidal geometry of the hypervalent compounds constructed by combination of Ge and azobenzene-based tridentate ligands. Experimental and theoretical calculation results disclosed that the germanium-nitrogen (Ge-N) coordination at the equatorial position strongly reduces the energy level of the LUMO (lowest unoccupied molecular orbital), and the three-center four-electron (3 c-4 e) bond in the apical position effectively rises the energy level of the HOMO (highest occupied molecular orbital). It is emphasized that large narrowing of the HOMO-LUMO energy gap is achieved just by forming the hypervalent bond. In addition, the narrow-energy-gap property can be enhanced by extension of π-conjugation. The obtained π-conjugated polymer shows efficient NIR emission both in solution (λ_PL =770 nm and Φ_PL =0.10) and film (λ_PL =807 nm and Φ_PL =0.04). These results suggest that collaboration of a hypervalent bond and a π-conjugated system is a novel and effective strategy for tuning electronic properties even in the NIR region.

Structural-Functional Properties of Asymmetric Fluoro-Alkoxy Substituted Benzothiadiazole Homopolymers with Flanked Chalcogen-Based Heterocycles

The synthesis and characterization of asymmetric alkoxy- are reported, fluoro-benzothiadiazole (BT) acceptor core derivatized with a series of six different heterocycles (selenophene, thiophene, furan, 5-thiazole, 2-thiazole and 2-oxazole). The effect of the flanked-heterocycles containing different chalcogen atoms of the six homopolymers (HPX) is studied using optical, thermal, electrochemical, and computational analysis. Computational calculations indicate a strong relationship between the most stable conformation for each homopolymer and their bearing heterocycle, thus homopolymers HPSe', HPTp', HPFu', and HPTzC5, adopted the syn-syn and syn-anti conformations due to their noncovalent interactions with shorter distances, while HPTzC2' and HPOx' demonstrate preference for the anti-anti conformation. Optical property studies of the homopolymers reveal a strong red-shift in solution and film upon exchanging the chalcogen atom from Oxygen < Sulfur < Selenium in HPFu, HPTp, and HPSe, respectively. In addition, deeper highest occupied molecular orbital (HOMO) energy levels are observed when the donor-acceptor moieties (HPSe, HPTp, and HPFu) are substituted for the acceptor-acceptor systems such as HPTzC5, HPTzC2, and HPOx. Improved packing and morphology are exhibited for the donor-acceptor homopolymers. Thus, having a flanked heterocycle containing different chalcogen-atoms in polymeric systems is one way of tuning the physicochemical properties of conjugated materials for optoelectronic applications.

Multicomponent Reaction of Isocyanide, Ditelluride, and Mn(III) Carboxylate: Synthesis of N-Acyl Tellurocarbamate

A multicomponent reaction of isocyanides, ditellurides and manganese(III) carboxylates under mild reaction conditions leads to the synthesis of various N-acyl tellurocarbamates. This method demonstrates good functional tolerance and broad substrate scope and, as a result, is especially suitable for the postfunctionalization of complicated molecules such as drugs. The given method can be further extended to the synthesis of selenocarbamates.

n-Type organic semiconducting polymers: stability limitations, design considerations and applications

This review outlines the design strategies which aim to develop high performing n-type materials in the fields of organic thin film transistors (OTFT), organic electrochemical transistors (OECT) and organic thermoelectrics (OTE). Figures of merit for each application and the limitations in obtaining these are set out, and the challenges with achieving consistent and comparable measurements are addressed. We present a thorough discussion of the limitations of n-type materials, particularly their ambient operational instability, and suggest synthetic methods to overcome these. This instability originates from the oxidation of the negative polaron of the organic semiconductor (OSC) by water and oxygen, the potentials of which commonly fall within the electrochemical window of n-type OSCs, and consequently require a LUMO level deeper than ∼-4 eV for a material with ambient stability. Recent high performing n-type materials are detailed for each application and their design principles are discussed to explain how synthetic modifications can enhance performance. This can be achieved through a number of strategies, including utilising an electron deficient acceptor-acceptor backbone repeat unit motif, introducing electron-withdrawing groups or heteroatoms, rigidification and planarisation of the polymer backbone and through increasing the conjugation length. By studying the fundamental synthetic design principles which have been employed to date, this review highlights a path to the development of promising polymers for n-type OSC applications in the future.

A tellura-Baeyer-Villiger oxidation: one-step transformation of tellurophene into chiral tellurinate lactone

Baeyer-Villiger (BV) oxidation is a fundamental organic reaction, whereas the hetero-BV oxidation is uncharted. Herein, a tellura-BV oxidation is discovered. By oxidizing a tellurophene-embedded and electron-rich polycycle (1) with mCPBA or Oxone, an oxygen atom is inserted into the Te-C bond of the tellurophene to form tellurinate lactone mono-2. This reaction proceeds as follows: (i) 1 is oxidized to the tellurophene Te-oxide form (IM-1); (ii) IM-1 undergoes tellura-BV oxidation to give mono-2. Moreover, the hybrid trichalcogenasumanenes 7 and 8 are, respectively, converted to tellurinate lactones mono-9 and mono-10 under the same conditions, indicating that tellura-BV oxidation shows high chemoselectivity. Due to the strong secondary bonding interactions between the Te[double bond, length as m-dash]O groups on tellurinate lactones, mono-2, mono-9, and mono-10 are dimerized to form U-shaped polycycles 2, 9, and 10, respectively. Notably, mono-2, mono-9, mono-10, and their dimers show chirality. This work enables one-step transformation of tellurophene into tellurinate lactone and construction of intricate polycycles.

Synthetic Routes for Heteroatom-Containing Alkylated/Arylated Polycyclic Aromatic Hydrocarbons

Synthetic routes for heteroatom-containing polycyclic aromatic hydrocarbons (H-PAHs) with alkyl and aryl substitution are demonstrated. Three H-PAHs, including heteroatom-containing rubicenes (H-rubicenes), angular-benzothiophenes (ABTs), and indenothiophene (IDTs) were successfully synthesized by two key steps, including polysubstituted olefin formation and cyclization. Specifically, ABT and H-rubicenes were comprehensively investigated by single-crystal X-ray diffraction, NMR spectroscopy, UV-vis absorption, cyclic voltammetry, transient absorption, and single-crystal OFET measurements.

Synergistic non-bonding interactions based on diketopyrrolo-pyrrole for elevated photoacoustic imaging-guided photothermal therapy

Synergistic non-bonding interactions in fluorine and chalcogen-substituted diketopyrrolopyrrole nanoagents for elevated photoacoustic imaging-guided photothermal therapy.

Terselenophene Regioisomer Conjugated Polymer Materials for High-Performance Cancer Phototheranostics

Molecular isomerization is a fundamental issue in the development of functional materials, with a crucial impact on photophysical properties. However, up to now, their effect on photothermal conversion is rarely investigated. Here, two near-infrared (NIR)-absorbing regioisomer conjugated polymers integrated with cis/trans-terselenophenes are designed and synthesized as efficient photothermal agents to enhance cancer phototheranostics. It is demonstrated that enhanced quinoidal resonance of trans-terselenophenes allows the resulting trans-CP to possess more planar backbone to further increase the effective conjugation length and result in the strong absorption spectra at 808 nm. Characterization of photophysical properties has proved that the photothermal conversion efficiency of trans-CP nanoparticles is up to 61.4%, and they are 210% as strong as cis-CP nanoparticles (29.4%). Further in vitro and in vivo works demonstrate efficient photothermal therapeutic effects with the guidance of photoacoustic imaging. This work affords a new understanding of the molecular isomerization into the development of conjugated materials for high-performance cancer phototheranostics.

Synthesis of side-chain regioregular and main-chain alternating poly(bichalcogenophene)s and an ABC-type periodic poly(terchalcogenophene)

Three unsymmetrical diiodobichalcogenophenes SSeI2, STeI2, and SeTeI2 and a diiodoterchalcogenophene SSeTeI2 were prepared. Grignard metathesis of SSeI2, STeI2, SeTeI2, and SSeTeI2 occurred regioselectively at the lighter chalcogenophene site because of its relatively lower electron density and less steric bulk. Nickel-catalyzed Kumada catalyst-transfer polycondensation of these Mg species provided a new class of side-chain regioregular and main-chain AB-type alternating poly(bichalcogenophene)s-PSSe, PSTe, and PSeTe-through a chain-growth mechanism. The ring-walking of the Ni catalyst from the lighter to the heavier chalcogenophene facilitated subsequent oxidative addition, thereby suppressing the possibility of chain-transfer or chain-termination. More significantly, the Ni catalyst could walk over the distance of three rings (ca. 1 nm)-from a thiophene unit via a selenophene unit to a tellurophene unit-to form PSSeTe, the first ABC-type regioregular and periodic poly(terchalcogenophene) comprising three different types of 3-hexylchalcogenophenes.

Pd(II)-Catalyzed Direct Dehydrogenative Mono- and Diolefination of Selenophenes

Pd(II)-catalyzed dehydrogenative Heck olefination of selenophenes with a broad olefinic substrate scope and high functional group tolerance is demonstrated. Carbonyl-substituted and phenyl-substituted olefins with electron-donating (D) and electron-accepting (A) groups can be regioselectively installed at C2 of the selenophene. The 2-olefinated selenophenes can subsequently undergo a second oxidative olefination to rapidly produce a new class of symmetrical D-π-D or unsymmetrical D-π-A 2,5-diolefinated selenophene materials.

The role of chemical design in the performance of organic semiconductors

Organic semiconductors are solution-processable, lightweight and flexible and are increasingly being used as the active layer in a wide range of new technologies. The versatility of synthetic organic chemistry enables the materials to be tuned such that they can be incorporated into biological sensors, wearable electronics, photovoltaics and flexible displays. These devices can be improved by improving their material components, not only by developing the synthetic chemistry but also by improving the analytical and computational techniques that enable us to understand the factors that govern material properties. Judicious molecular design provides control of the semiconductor frontier molecular orbital energy distribution and guides the hierarchical assembly of organic semiconductors into functional films where we can manipulate the properties and motion of charges and excited states. This Review describes how molecular design plays an integral role in developing organic semiconductors for electronic devices in present and emerging technologies.

Double Chalcogen Bonds: Crystal Engineering Stratagems via Diffraction and Multinuclear Solid-State Magnetic Resonance Spectroscopy

Group 16 chalcogens potentially provide Lewis-acidic σ-holes, which are able to form attractive supramolecular interactions with electron rich partners through chalcogen bonds. Here, a multifaceted experimental and computational study of a large series of novel chalcogen-bonded cocrystals, prepared using the principles of crystal engineering, is presented. Single-crystal X-ray diffraction studies reveal that dicyanoselenadiazole and dicyanotelluradiazole derivatives work as promising supramolecular synthons with the ability to form double chalcogen bonds with a wide range of electron donors including halides and oxygen- and nitrogen-containing heterocycles. Extensive ⁷⁷ Se and ¹²⁵ Te solid-state nuclear magnetic resonance spectroscopic investigations of cocrystals establish correlations between the NMR parameters of selenium and tellurium and the local chalcogen bonding geometry. The relationships between the electronic environment of the chalcogen bond and the ⁷⁷ Se and ¹²⁵ Te chemical shift tensors were elucidated through a natural localized molecular orbital density functional theory analysis. This systematic study of chalcogen-bond-based crystal engineering lays the foundations for the preparation of the various multicomponent systems and establishes solid-state NMR protocols to detect these interactions in powdered materials.

Tailor-made chalcogen-rich polycarbonates: experimental and computational insights into chalcogen group-dependent ring opening polymerization

A versatile strategy to poly(chalcogen-carbonate) library is presented by organic base catalytic macrocarbonate polymerization. Polymerization depends sensitively on chalcogen groups.

Synthesis of Tellurium-Containing π-Extended Aromatics with Room-Temperature Phosphorescence

A synthesis of tellurium-embedded π-extended aromatics from tellurium powder and readily available cyclic diaryliodonium salts has been developed. The versatility of this method has been demonstrated by the synthesis of various functionalized dibenzotellurophenes (DBTe's), a ladder-type π-system, and a heterosumanene. These compounds demonstrated good air/moisture stability and high thermal stability. Remarkably, many DBTe's exhibited interesting tunable room-temperature phosphorescence (RTP) in the solid state.

Furan-flanked diketopyrrolopyrrole-based chalcogenophene copolymers with siloxane hybrid side chains for organic field-effect transistors

Furan-flanked diketopyrrolopyrrole-based chalcogenophene copolymers are synthesized for the comprehensive study of the heterocyclic effect in organic field-effect transistors.

Trichalcogenasumanenes containing various chalcogen atoms: synthesis, structure, properties, and chemical reactivity

Trichalcogenasumanenes containing two kinds of chalcogen are synthesized. The majority chalcogen governs the optical properties and the heavier chalcogen governs the chemical reactivity.

Chalcogen bonding in synthesis, catalysis and design of materials

Chalcogen bonding is a type of noncovalent interaction in which a covalently bonded chalcogen atom (O, S, Se or Te) acts as an electrophilic species towards a nucleophilic (negative) region(s) in another or in the same molecule. In general, this interaction is strengthened by the presence of an electron-withdrawing group on the electron-acceptor chalcogen atom and upon moving down in the periodic table of elements, from O to Te. Following a short discussion of the phenomenon of chalcogen bonding, this Perspective presents some demonstrative experimental observations in which this bonding is crucial for synthetic transformations, crystal engineering, catalysis and design of materials as synthons/tectons.

2,5-Diaryltellurophenes: Effect of Electron-Donating and Electron-Withdrawing Groups on their Optoelectronic Properties

The transformation of 1,2-bis(1-arylvinyl)ditellurides into 2,5-diaryltellurophenes by sequential ditelluride exchange and thermal intramolecular cyclization reactions is presented, and the optoelectronic properties of a series of 2,5-diaryltellurophenes with both electron-donating and electron-withdrawing aryl substituents are disclosed. Furthermore, the multicolored emissive tellurophenes in solution at room temperature have been demonstrated.

Synthesis of unsymmetrical benzotrichalcogenophenes by N-heterocyclic carbene-palladium-catalyzed intramolecular direct C3-arylation of chalcogenophenes

A series of new unsymmetrical benzotrichalcogenophenes (BTCs) were synthesized by the Pd-N-heterocyclic carbene catalyzed intramolecular C3-arylation of furan, thiophene, selenophene and tellurophene units. This is the first time that a C3-direct arylation of selenophene and tellurophene moieties has ever been demonstrated.

Tritellurasumanene: ultrasound assisted one-pot synthesis and extended valence adducts with bromine

Tritellurasumanene is synthesized from a triphenylene skeleton via ultrasound assisted one-pot reaction. This compound adopts a flat conjugated system and displays TeTe (3.83 Å) interactions in the solid state. Its optical properties and chemical reactivity are quite different from those of its trithia- and triselena-analogues.

Chalcogen atom modulated persistent room-temperature phosphorescence through intramolecular electronic coupling

A series of novel persistent room-temperature phosphorescence (pRTP) materials (PEPCz) obtainedviaa combination of chalcogen atoms (O, S, Se, and Te) and a carbazolyl moiety is reported.

Versatile telluracycle synthesis via the sequential electrophilic telluration of C(sp2)-Zn and C(sp2)-H bonds

We report herein a new approach for the synthesis of tellurium-bridged aromatic compounds based on the sequential electrophilic telluration of C(sp2)-Zn and C(sp2)-H bonds with tellurium(iv) chlorides. A combination of transition metal-catalyzed (migratory) arylmetalation of alkynes and sequential telluration allows for the expedient construction of a library of functionalized benzo[b]tellurophenes. Furthermore, a variety of heteroarene-fused benzotellurophenes and other novel tellurium-embedded polycyclic aromatics can be readily synthesized from the corresponding 2-iodoheterobiaryls.

Excitation Intensity Dependent Carrier Dynamics of Chalcogen Heteroatoms in Medium-Bandgap Polymer Solar Cells

The excitation intensity dependent carrier dynamics of blends with PC[70]BM of three new medium-band gap conjugated polymers with central chalcogen heteroatoms, PBDTfDTBX (X = O, T(Sulphur), Se) were studied. The PBDTfDTBX polymers (Poly[4,8-bis(5-(2-butyloctyl)thiophene-2-yl)benzo[1,2-b;4,5-b′]dithiophene-alt-4,7-bis(4-(2-ethylhexyl)-2-thienyl)-dithieno[3′,2′:3,4;2″,3″:5,6]benzo[1,2-c][1,2,5] furazan or thiadiazole or selenadiazole]) have symmetrical structures but exhibit different solar cell performances. In this study, we determined how the photogenerated charge carrrier dynamics of the PBDTfDTBX:PC[70]BM blends varies with the heteroatom by performing transient absorption measurements at various excitation intensities. It was found that the charge carrier dynamics of the PBDTfDTBX blends with X = T or Se heteroatoms are dependent on the excitation intensity whereas that of the PBDTfDTBO blend is independent of the intensity. The photogenerated charge carrier dynamics of the PBDTfDTBO:PCBM, PBDTfDTBT:PCBM, and PBDTfDTBSe:PCBM blends were all modeled globally and rates were estimated for different photophysical processes occurring on different time scales.

Tellurophene-Based N-type Copolymers for Photovoltaic Applications

Novel tellurophene-based n-type copolymers are synthesized and characterized with thermal analysis, electrochemistry, optical spectroscopy, and DFT calculations. The copolymers demonstrate reversible interactions with bromine. Through tuning of the building blocks and alkyl chains together with device engineering, the maximum power conversion efficiency of all-polymer solar cells improves from 2.8 to 4.3%, which is supported by photoluminescence, atomic force microscopy, transmission electron microscopy, the space charge limit current method, and exciton dynamic studies. These results suggest that tellurophene-based n-type copolymers are promising electron acceptors for organic solar cells and potential sensor materials for bromine detection.

Air-Stable n-channel Diketopyrrolopyrrole-Diketopyrrolopyrrole Oligomers for High Performance Ambipolar Organic Transistors

n-channel organic semiconductors are prone to oxidation upon exposed to ambient conditions. Herein, we report design and synthesis of diketopyrrolopyrrole (DPP)-based oligomers for ambipolar organic thin-film transistors (OFETs) with excellent air and bias stability at ambient conditions. The cyclic voltammetry measurements reveal exceptional electrochemical stability during the redox cycle of oligomers. Structural properties including aggregation, crystallinity, and morphology in thin film were investigated by UV-visible spectroscopy, atomic force microscopy (AFM), thin-film X-ray diffraction (XRD), and grazing incidence small-angle X-ray scattering (GISAXS) measurements. AFM reveals morphological changes induced by different processing conditions whereas GISAXS measurements show an increase in the population of face-on oriented crystallites in films subjected to a combination of solvent and thermal treatments. These measurements also highlight the significance of chalcogen atom from sulfur to selenium on the photophysical, optical, electronic, and solid-state properties of DPP-DPP oligomers. Charge carrier mobilities of the oligomers were investigated by fabricating top-gate bottom-contact (TG-BC) thin-film transistors by annealing the thin films under various conditions. Combined solvent and thermal annealing of DPP-DPP oligomer thin films results in consistent electron mobilities as high as ∼0.2 cm(2) V(-1) s(-1) with an on/off ratio exceeding 10(4). Field-effect behavior was retained for up to ∼4 weeks, which illustrates remarkable air and bias stability. This work paves the way toward the development of n-channel DPP-DPP-based oligomers exhibiting retention of field-effect behavior with superior stability at ambient conditions.

Influence of the heteroatom on the optoelectronic properties and transistor performance of soluble thiophene-, selenophene- and tellurophene-vinylene copolymers

We report the first soluble poly(3-dodecyl tellurophenylene-vinylene) polymer (P3TeV) by Stille copolymerization and compare its properties to the analogous thiophene and selenophene containing polymers. The optical band gap of the polymers is shown to systematically decrease as the size of the heteroatom is increased, mainly as a result of a stabilization of the LUMO energy, resulting in a small band gap of 1.4 eV for P3TeV. Field effect transistors measurements in variety of architectures demonstrate that the selenophene polymer exhibits the highest mobility, highlighting that increasing the size of the heteroatom is not always beneficial for charge transport.

Synthesis and field-effect transistor properties of a diseleno[3,2-b:2′,3′-d]silole-based donor–acceptor copolymer: investigation of chalcogen effect

We have designed and synthesized a tricyclic diseleno[3,2-b:2′,3′-d]silole (DSS) wherein the 3,3′-position of a biselenophene is bridged by a dioctylsilyl moiety.

Polymers and the p-block elements

A survey of the state-of-the-art in the development of synthetic methods to incorporate p-block elements into polymers is given. The incorporation of main group elements (groups 13-16) into long chains provides access to materials with fascinating chemical and physical properties imparted by the presence of inorganic groups. Perhaps the greatest impedance to the widespread academic and commercial use of p-block element-containing macromolecules is the synthetic challenge associated with linking inorganic elements into long chains. In recent years, creative methodologies have been developed to incorporate heteroatoms into polymeric structures, with perhaps the greatest advances occurring with hybrid organic-inorganic polymers composed of boron, silicon, phosphorus and sulfur. With these developments, materials are currently being realized that possess exciting chemical, photophysical and thermal properties that are not possible for conventional organic polymers. This review focuses on highlighting the most significant recent advances whilst giving an appropriate background for the general reader. Of particular focus will be advances made over the last two decades, with emphasis on the novel synthetic methodologies employed.

Chalcogenophene comonomer comparison in small band gap diketopyrrolopyrrole-based conjugated polymers for high-performing field-effect transistors and organic solar cells

The design, synthesis, and characterization of a series of diketopyrrolopyrrole-based copolymers with different chalcogenophene comonomers (thiophene, selenophene, and tellurophene) for use in field-effect transistors and organic photovoltaic devices are reported. The effect of the heteroatom substitution on the optical, electrochemical, and photovoltaic properties and charge carrier mobilities of these polymers is discussed. The results indicate that by increasing the size of the chalcogen atom (S < Se < Te), polymer band gaps are narrowed mainly due to LUMO energy level stabilization. In addition, the larger heteroatomic size also increases intermolecular heteroatom-heteroatom interactions facilitating the formation of polymer aggregates leading to enhanced field-effect mobilities of 1.6 cm(2)/(V s). Bulk heterojunction solar cells based on the chalcogenophene polymer series blended with fullerene derivatives show good photovoltaic properties, with power conversion efficiencies ranging from 7.1-8.8%. A high photoresponse in the near-infrared (NIR) region with excellent photocurrents above 20 mA cm(-2) was achieved for all polymers, making these highly efficient low band gap polymers promising candidates for use in tandem solar cells.

Influences of the backbone randomness on the properties, morphology and performances of the fluorinated benzoselenadiazole–benzothiadiazole based random copolymers

A series of FBT–FBSe ternary random copolymers were synthesized to identify the influences of backbone randomness on the morphology and performances.