Siloxane‐Based Hybrid Semiconducting Polymers Prepared by Fluoride‐Mediated Suzuki Polymerization

Siloxane‐containing materials are a large and important class of organic‐inorganic hybrids. In this report, a practical variation of the Suzuki polymerization to generate semiconducting polymeric hybrids based on siloxane units, which proceeds under essentially nonbasic conditions, is presented. This method generates solution‐processable poly(diketopyrrolopyrrole‐alt‐benzothiadiazole) (PDPPBT‐Si) consisting of the hybrid siloxane substituents, which could not be made using conventional methods. PDPPBT‐Si exhibits excellent ambipolar transistor performance with well‐balanced hole and electron FET mobilities. The siloxane‐containing DPP‐thiophene polymer classes (PDPP3T‐Si and PDPP4T‐Si), synthesized by this method, exhibit high hole mobility of up to 1.29 cm² V^?1 s^?1. This synthetic approach should provide access to a variety of novel siloxane‐containing conjugated semiconductor classes by using a variety of aryldihalides and aryldiboronic acids/esters.     

HOMO Stabilisation in π‐Extended Dibenzotetrathiafulvalene Derivatives for Their Application in Organic Field‐Effect Transistors

Three new organic semiconductors, in which either two methoxy units are directly linked to a dibenzotetrathiafulvalene (DB‐TTF) central core and a 2,1,3‐chalcogendiazole is fused on the one side, or four methoxy groups are linked to the DB‐TTF, have been synthesised as active materials for organic field‐effect transistors (OFETs). Their electrochemical behaviour, electronic absorption and fluorescence emission as well as photoinduced intramolecular charge transfer were studied. The electron‐withdrawing 2,1,3‐chalcogendiazole unit significantly affects the electronic properties of these semiconductors, lowering both the HOMO and LUMO energy levels and hence increasing the stability of the semiconducting material. The solution‐processed single‐crystal transistors exhibit high performance with a hole mobility up to 0.04 cm² V^?1 s^?1 as well as good ambient stability.     

Carbazolyl Benzo[1,2‐b:4,5‐b′]difuran: An Ambipolar Host Material for Full‐Color Organic Light‐Emitting Diodes

We have designed an ambipolar material, 3,7‐bis[4‐(N‐carbazolyl)‐phenyl]‐2,6‐diphenylbenzo[1,2‐b:4,5‐b′]difuran (CZBDF), and synthesized it by zinc‐mediated double cyclization. Its physical properties clarified that CZBDF possesses a wide‐gap character, well‐balanced and high hole and electron mobilities of larger than 10^?3 cm² V^?1 s^?1, and a high thermal stability. Using CZBDF as a host material for heterojunction OLED devices, a full range of visible emission was obtained. Notably, CZBDF also enabled us to fabricate RGB‐emitting homojunction OLEDs, with performances comparable or superior to the heterojunction devices composed of several materials.     

Diketopyrrolopyrrole‐Porphyrin Based Conjugated Polymers for Ambipolar Field‐Effect Transistors

Porphyrin‐based molecules have been widely used in dye‐sensitized solar cells and bulk heterojunction solar cells, but their application in field‐effect transistors (FETs) is limited. In this work, two conjugated polymers based on diketopyrrolopyrrole and porphyrin units were developed for FETs. The polymers exhibit extra‐low band gap with energy levels close to −4.0 eV and −5.0 eV due to the strong electron‐donating and withdrawing ability of porphyrin and diketopyrrolopyrrole. With additionally high crystalline properties, ambipolar charge carrier transports with a hole mobility of 0.1 cm² V⁻¹ s⁻¹ in FETs were realized in these polymers, representing the highest performance in solution‐processed FETs based on porphyrin unit.     

Extended Conjugated Donor–Acceptor Molecules with E‐(1,2‐Difluorovinyl) and Diketopyrrolopyrrole (DPP) Moieties toward High‐Performance Ambipolar Organic Semiconductors

Two diketopyrrolopyrrole (DPP)‐based donor–acceptor (D–A) conjugated molecules, DPP‐F and DPP‐2F, which contain E‐(1,2‐difluorovinyl) moieties, are reported. The LUMO energies of DPP‐F and DPP‐2F were estimated to be ?3.49 and ?3.70 eV, respectively, based on their redox potentials and absorption spectral data; these values were clearly lowered because of the incorporation of electron‐withdrawing E‐(1,2‐difluorovinyl) moieties. Organic field‐effect transistors (OFETs) with thin films of DPP‐F and DPP‐2F were successfully fabricated with conventional techniques. Based on the respective transfer and output characteristics measured in an inert atmosphere, thin films of DPP‐2F display ambipolar semiconducting behavior with hole and electron mobilities reaching 0.42 and 0.80 cm² V^?1 s^?1, respectively. The as‐prepared OFET of DPP‐2F already shows high hole and electron mobilities that are not influenced remarkably by thermal annealing. For thin films of DPP‐F, only p‐type semiconducting behavior was observed in both an inert atmosphere and air, and the hole mobility increased to 0.1 cm² V^?1 s^?1 after thermal annealing. XRD and AFM studies were performed with thin films of DPP‐F and DPP‐2F after annealing at different temperatures.     

Selenophene‐Flanked Diketopyrrolopyrrole Based Conjugated Polymers for Ambipolar Field‐Effect Transistors

The development of selenophene‐flanked DPP (SeDPP) based copolymers, especially for the ambipolar ones, lags behind other aromatic group flanked DPP‐based polymers. Herein, we report two new ambipolar SeDPP‐based conjugated polymers. One is the alternating polymer PSeDPPFT with normal SeDPP and 3,4‐difluorothiophene units. The other is PSeFDFT , in which the electron acceptor unit is replaced by a new SeDPP derivative, referred as to half‐fused SeDPP. The more planar structure of half‐fused SeDPP endows the backbone of PSeFDFT with good rigidity and planarity. Both polymers exhibit ambipolar transporting properties in air. The PSeFDFT based field‐effect transistors (FETs) display higher and more balanced ambipolar properties with μ_h^ave of 0.27 cm²·V^–1·s^–1, μ_e^ave of 0.18 cm²·V^–1·s^–1, and μ_h^ave/μ_e^ave of 1.5 than those of PSeDPPFT (μ_h^ave = 0.11 cm²·V^–1·s^–1, μ_e^ave = 0.042 cm²·V^–1·s^–1, and μ_h/μ_e = 2.6). This is attributed to the more planar structure, lower LUMO level, higher HOMO level, and better interchain packing orientations of PSeFDFT by comparing with PSeDPPFT . Therefore, a new molecular design strategy to modulate the hole and electron transporting properties is proposed for conjugated D‐A polymers.     

Benzodifuran‐containing well‐defined π‐conjugated polymers for photovoltaic cells

Two well‐defined alternating π‐conjugated polymers containing a soluble electroactive benzo[1,2‐b:4,5‐b′]difuran (BDF) chromophore, poly(BDF‐(9‐phenylcarbazole)) (PBDFC), and poly(BDF‐benzothiadiazole) (PBDFBTD) were synthesized via Sonogashira copolymerizations. Their optical, electrochemical, and field‐effect charge transport properties were characterized and compared with those of the corresponding homopolymer PBDF and random copolymers of the same overall composition. All these polymers cover broad optical absorption ranges from 250 to 750 nm with narrow optical band gaps of 1.78–2.35 eV. Both PBDF and PBDFBTD show ambipolar redox properties with HOMO levels of ?5.38 and ?5.09 eV, respectively. The field‐effect mobility of holes varies from 2.9 × 10^?8 cm² V^?1 s^?1 in PBDF to 1.0 × 10^?5 cm² V^?1 s^?1 in PBDFBTD. Bulk heterojunction solar cell devices were fabricated using the polymers as the electron donor and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester as the electron acceptor, leading to power conversion efficiencies of 0.24–0.57% under air mass 1.5 illumination (100 mW cm^?2). These results indicate that their band gaps, molecular electronic energy levels, charge mobilities, and molecular weights are readily tuned by copolymerizing the BDF core with different π‐conjugated units. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Modulation of electronic properties of π‐conjugated copolymers derived from naphtho[1,2‐b:5,6‐b′]dithiophene donor unit: A structure‐property relationship study

A set of three donor‐acceptor conjugated (D‐A) copolymers were designed and synthesized via Stille cross‐coupling reactions with the aim of modulating the optical and electronic properties of a newly emerged naphtho[1,2‐b:5,6‐b′]dithiophene donor unit for polymer solar cell (PSCs) applications. The PTNDTT‐BT , PTNDTT‐BTz , and PTNDTT‐DPP polymers incorporated naphtho[1,2‐b:5,6‐b′]dithiophene ( NDT ) as the donor and 2,2′‐bithiazole ( BTz ), benzo[1,2,5]thiadiazole ( BT ), and pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione ( DPP ), as the acceptor units. A number of experimental techniques such as differential scanning calorimetry, thermogravimetry, UV–vis absorption spectroscopy, cyclic voltammetry, X‐ray diffraction, and atomic force microscopy were used to determine the thermal, optical, electrochemical, and morphological properties of the copolymers. By introducing acceptors of varying electron withdrawing strengths, the optical band gaps of these copolymers were effectively tuned between 1.58 and 1.9 eV and their HOMO and LUMO energy levels were varied between ?5.14 to ?5.26 eV and ?3.13 to ?3.5 eV, respectively. The spin‐coated polymer thin film exhibited p‐channel field‐effect transistor properties with hole mobilities of 2.73 × 10^?3 to 7.9 × 10^?5 cm² V^?1 s^?1. Initial bulk‐heterojunction PSCs fabricated using the copolymers as electron donor materials and [6,6]‐phenyl C71 butyric acid methyl ester (PC₇₁BM) as the acceptor resulted in power conversion efficiencies in the range of 0.67–1.67%. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2948–2958     

Dithienocyclopentathieno[3,2‐b]thiophene Hexacyclic Arene for Solution‐Processed Organic Field‐Effect Transistors and Photovoltaic Applications

We have developed a ladder‐type dithienocyclopentathieno[3,2‐b]thiophene ( DTCTT ) hexacyclic unit in which the central thieno[3,2‐b]thiophene ring was covalently fastened to two adjacent thiophene rings through carbon bridges, thereby forming two connected cyclopentadithiophene ( CPDT ) units in a hexacyclic coplanar structure. This stannylated Sn‐DTCTT building block was copolymerized with three electron‐deficient acceptors, dibromo‐thieno[3,4‐c]pyrrole‐4,6‐dione ( TPD ), dibromo‐benzothiadiazole ( BT ), and dibromo‐phenanthrenequinoxaline ( PQX ), by Stille polymerization, thereby furnishing a new class of alternating donor–acceptor copolymers: PDTCTTTPD , PDTCTTBT , and PDTCTTPQX , respectively. Field‐effect transistors based on PDTCTTPQX and PDTCTTBT yielded high hole mobilities of 0.017 and 0.053 cm² V^?1 s^?1, respectively, which are among the highest performances among amorphous donor–acceptor copolymers. A bulk heterojunction solar cell that incorporated PDTCTTTPD with the lower‐lying HOMO energy level delivered a higher V_oc value of 0.72 V and a power conversion efficiency (PCE) value of 2.59 %.     

Dithienoindophenines: p‐Type Semiconductors Designed by Quinoid Stabilization for Solar‐Cell Applications

Compared with the dominant aromatic conjugated materials, photovoltaic applications of their quinoidal counterparts featuring rigid and planar molecular structures have long been unexplored despite their narrow optical bandgaps, large absorption coefficients, and excellent charge‐transport properties. The design and synthesis of dithienoindophenine derivatives (DTIPs) by stabilizing the quinoidal resonance of the parent indophenine framework is reported here. Compared with the ambipolar indophenine derivatives, DTIPs with the fixed molecular configuration are found to be p‐type semiconductors exhibiting excellent unipolar hole mobilities up to 0.22 cm² V^?1 s^?1, which is one order of magnitude higher than that of the parent IP‐O and is even comparable to that of QQT(CN)4‐based single‐crystal field‐effect transistors (FET). DTIPs exhibit better photovoltaic performance than their aromatic bithieno[3,4‐b]thiophene (BTT) counterparts with an optimal power‐conversion efficiency (PCE) of 4.07 %.     

Simultaneous morphological stability and high charge carrier mobilities in donor–acceptor block copolymer/PCBM blends

Donor–acceptor block copolymers (BCP), incorporating poly(3‐hexylthiophene) (P3HT), and a polystyrene copolymer with pendant fullerenes (PPCBM) provide desired stable nanostructures, but mostly do not exhibit balanced charge carrier mobilities. This work presents an elegant approach to match hole and electron transport in BCP by blending with molecular PCBM without causing any macrophase separation. An insufficient electron mobility of PPCBM can be widely compensated by adding PCBM which is monitored by the space‐charge limited current method. Using X‐ray diffraction, atomic force microscopy, and differential scanning calorimetry, we verify the large miscibility of the PPCBM:PCBM blend up to 60 wt % PCBM load forming an amorphous, molecularly mixed fullerene phase without crystallization. Thus, blending BCP with PCBM substantially enhances charge transport achieving an electron mobility of μ_e=(3.2 ± 1.7) × 10^?4 cm²V^?1s^?1 and hole mobility of μ_h=(1.8 ± 0.6) × 10^?3 cm²V^?1s^?1 in organic field‐effect transistors (OFET). The BCP:PCBM blend provides a similarly high ambipolar charge transport compared to the established P3HT:PCBM system, but with the advantage of an exceptionally stable morphology even for prolonged thermal annealing. This work demonstrates the feasibility of high charge transport and stable morphology simultaneously in a donor–acceptor BCP by a blend approach. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1125–1136     

Electronic structure and microscopic charge‐transport properties of a new‐type diketopyrrolopyrrole‐based material

Recently, diketopyrrolopyrrole (DPP)‐based materials have attracted much interest due to their promising performance as a subunit in organic field effect transistors. Using density functional theory and charge‐transport models, we investigated the electronic structure and microscopic charge transport properties of the cyanated bithiophene‐functionalized DPP molecule (compound 1 ). First, we analyzed in detail the partition of the total relaxation (polaron) energy into the contributions from each vibrational mode and the influence of bond‐parameter variations on the local electron–vibration coupling of compound 1 , which well explains the effects of different functional groups on internal reorganization energy (λ). Then, we investigated the structural and electronic properties of compound 1 in its isolated molecular state and in the solid state form, and further simulated the angular resolution anisotropic mobility for both electron‐ and hole‐transport using two different simulation methods: (i) the mobility orientation function proposed in our previous studies (method 1); and (ii) the master equation approach (method 2). The calculated electron‐transfer mobility (0.00003–0.784 cm² V^?1 s^?1 from method 1 and 0.02–2.26 cm² V^?1 s^?1 from method 2) matched reasonably with the experimentally reported value (0.07–0.55 cm² V^?1 s^?1). To the best of our knowledge, this is the first time that the transport parameters of compound 1 were calculated in the context of band model and hopping models, and both calculation results suggest that the intrinsic hole mobility is higher than the corresponding intrinsic electron mobility. Our calculation results here will be instructive to further explore the potential of other higher DPP‐containing quinoidal small molecules. © 2015 Wiley Periodicals, Inc.     

Solution‐Processable n‐Type Organic Field‐Effect Transistor (OFET) Materials Based on Carbonyl‐Bridged Bithiazole and Dioxocyclopentene‐Annelated Thiophenes

A series of electronegative π‐conjugated compounds composed of carbonyl‐bridged bithiazole and alkyl‐substituted dioxocyclopenta[b]thiophene were synthesized as a candidate for solution‐processable n‐type organic semiconductor materials and characterized on the basis of photophysical and electrochemical properties. Cyclic voltammetry measurements showed that the first half‐wave reduction potentials of these compounds are between −0.97 and −1.14 V versus ferrocene/ferrocenium, which corresponds to lowest unoccupied molecular orbital energy levels between −3.83 and −3.66 eV. Thanks to hexyl or dodecyl groups in the molecules, the compounds are sufficiently soluble to realize the fabrication of their thin films through a spin‐coating method. As a result, the prepared organic field‐effect transistors based on these newly developed compounds exhibited n‐channel characteristics not only under vacuum but also in air, and the best field‐effect electron mobility observed under vacuum was 0.011 cm² V⁻¹ s⁻¹ with an on/off ratio of 10⁸ and a threshold voltage of 16 V.     

Synthesis and characterization of a novel ambipolar polymer semiconductor based on a fumaronitrile core as an electron‐withdrawing group

Two conjugated polymers containing stilbene and fumaronitrile moieties were synthesized to investigate their electronic properties by the existence of electron‐withdrawing cyano groups on a vinylene backbone. The cyclic voltammetry investigation and time‐dependent density functional theory calculations indicated that the cyano substituents lowered the lowest unoccupied molecular orbital (LUMO) energy level by about 0.65 and 0.63 eV, respectively. The lowering of the LUMO energy levels due to the electron‐withdrawing properties of the cyano substituents could enhance electron injection capability. Furthermore, bithiophene‐fumaronitrile (donor‐acceptor) intermolecular interaction facilitates the self‐assembly of the polymer chains. Organic field‐effect transistors (OFETs) based on PBTSB without the electron‐withdrawing group only exhibit hole transport, while OFETs based on PBTFN with cyano substituents exhibit ambipolar characteristics. The growth of PBTFN crystalline fibrils was observed with increasing annealing temperature, which enhanced hole and electron mobility. A complementary‐like inverter using PBTFN with ambipolar properties exhibited good symmetry with an inverting voltage nearly half that of the power supply with a gain of 9 at V_DD = 100 V. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

A Planarized Triphenylborane Mesogen: Discotic Liquid Crystals with Ambipolar Charge‐Carrier Transport Properties

A discotic liquid‐crystalline (LC) material, consisting of a planarized triphenylborane mesogen, was synthesized. X‐ray diffraction analysis confirmed that this compound forms a hexagonal columnar LC phase with an interfacial distance of 3.57 Å between the discs. At ambient temperature, this boron‐centered discotic liquid crystal exhibited ambipolar carrier transport properties with electron and hole mobility values of approximately 10^?3 and 3×10^?5 cm² V^?1 s^?1, respectively.     

Synthesis and FET characterization of novel ambipolar and low‐bandgap naphthalene‐diimide‐based semiconducting polymers

A novel series of naphthalene‐diimide‐based semiconducting polymers ( P1–P4 ) containing benzodithiophene or dithienopyrrole were successfully synthesized for ambipolar semiconducting materials showing near infrared absorptions. The incorporation of a 3‐hexylthiophene (3HT) spacer extended the intramolecular charge‐transfer (ICT) peak from λ_onset = 739 nm ( P1 ) to 785 nm ( P3 ). Moreover, about 250 nm red‐shift of the ICT peaks was observed in P2 and P4 compared to P1 and P3 due to the increased high‐lying HOMO energy levels. The grazing incidence X‐ray scattering of the P3 and P4 films proved the slightly improved crystalline order in the π?π stacking direction, indicating that the planar backbone is probably due to the introduced 3HT. The P1–P4 ‐based field‐effect transistor showed n‐type dominant ambipolar characteristics. The P2 and P4 showed higher electron mobilities up to 1.5 × 10^?2 cm² V^?1 s^?1 than P1 and P3 , which might be influenced by the orientation of the polymer backbone and the intermolecular orbital overlap. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 359–367     

Thiophene‐S,S‐dioxidized Indophenine: A Quinoid‐Type Building Block with High Electron Affinity for Constructing n‐Type Polymer Semiconductors with Narrow Band Gaps

Three thiophene‐S,S‐dioxidized indophenine (IDTO) isomers, 3 a (E,E,E), 3 b (Z,E,E), and 3 c (Z,E,Z), were synthesized by oxidation of an indophenine compound. 3 b and 3 c could be converted into the most‐stable 3 a by heating at 110 °C. An IDTO‐containing conjugated polymer, PIDTOTT, was prepared using 3 a as a comonomer through a Stille coupling reaction, and it possesses a narrow band gap and low energy levels. In organic field effect transistors (OFETs), PIDTOTT exhibited unipolar n‐type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm² V^?1 s^?1), despite its rather disordered chain packing.     

Synthesis,characterization, and organic field‐effect transistors study of conjugated D–A copolymers based on dialkylated naphtho[1,2‐b:5,6‐b′]dithiophene/naphtho[1,2‐b:5,6‐b′]difuran and benzodiathiazole/benzoxadiazole

In this report, four donor–acceptor copolymers, P(NDT3‐BT), P(NDT3‐BO), P(NDF3‐BT), and P(NDF3‐BO), using 5,10‐didodecyl‐naphtho[1,2‐b:5,6‐b′]dithiophene (NDT3) or 5,10‐didodecyl‐naphtho[1,2‐b:5,6‐b′]difuran (NDF3) as an electron‐rich unit and benzodiathiazole (BT) or benzoxadiazole (BO) as an electron‐deficient one, were designed, synthesized, and characterized. Detailed systematical investigation was developed for studying the effect of the S/O atoms on the optical, electrochemical, and morphological properties of the polymers, as well as the subsequent performance of the organic field‐effect transistors (OFETs) fabricated from these copolymers. It was found that, compared with NDF3‐based P(NDF3‐BT)/P(NDF3‐BO), by replacing NDF3 with stronger aromatic NDT3, the resultant P(NDT3‐BT)/P(NDT3‐BO) show smaller lamellar distance with an increased surface roughness in solid state, and relatively higher hole mobilities are obtained. The hole mobilities of the four polymers based on OFETs varied from 0.20 to 0.32 cm² V^?1 s^?1 depending on their molecular structures, giving some valuable insights for the further design and development of a new generation of semiconducting materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2465–2476     

Synthesis and characterization of fused‐thiophene containing naphthalene diimide n‐type copolymers for organic thin film transistor and all‐polymer solar cell applications

Naphthalene diimide copolymers are attractive n‐type materials due to their high electron affinities, high electron mobilities, and exceptional stability. Herein, we report a series of NDI‐fused‐thiophene based copolymers with each copolymer differing in the number of fused thiophenes in the donor monomer. Increasing the number of fused‐thiophene moieties within an NDI‐copolymer backbone is shown to not only enable tuning of the electronic structure but also improve charge mobilities within the active layer of organic field‐effect transistors. Electron mobilities and on/off ratios as high as 0.012 cm² V^?1 s^‐1 and I_on/I_off > 10⁵ were measured from n‐channel thin‐film transistors fabricated using NDI‐xfTh copolymers. Bulk heterojunction solar cell devices were also fabricated from the NDI‐xfTh copolymer series in blends with poly(3‐hexylthiophene) (P3HT) with PNDI‐4fTh ‐ based devices yielding the largest J_sc (0.57 mA cm^?2) and fill factor (55%) in addition to the highest measured PCE for this series (0.13%). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4061–4069     

Incorporation of 2,6‐Connected Azulene Units into the Backbone of Conjugated Polymers: Towards High‐Performance Organic Optoelectronic Materials

Azulene is a promising candidate for constructing optoelectronic materials. An effective strategy is presented to obtain high‐performance conjugated polymers by incorporating 2,6‐connected azulene units into the polymeric backbone, and two conjugated copolymers P(TBAzDI‐TPD) and P(TBAzDI‐TFB) were designed and synthesized based on this strategy. They are the first two examples for 2,6‐connected azulene‐based conjugated polymers and exhibit unipolar n‐type transistor performance with an electron mobility of up to 0.42 cm² V^?1 s^?1, which is among the highest values for n‐type polymeric semiconductors in bottom‐gate top‐contact organic field‐effect transistors. Preliminary all‐polymer solar cell devices with P(TBAzDI‐TPD) as the electron acceptor and PTB7‐Th as the electron donor display a power conversion efficiency of 1.82 %.