Synthesis of Poly(benzothiadiazole‐co‐dithienobenzodithiophenes) and Effect of Thiophene Insertion for High‐Performance Polymer Solar Cells

We describe herein the synthesis of novel donor–acceptor conjugated polymers with dithienobenzodithiophenes (DTBDT) as the electron donor and 2,1,3‐benzothiadiazole as the electron acceptor for high‐performance organic photovoltaics (OPVs). We studied the effects of strategically inserting thiophene into the DTBDT as a substituent on the skeletal structure on the opto‐electronic performances of fabricated devices. From UV/Vis absorption, electrochemical, and field‐effect transistor analyses, we found that the thiophene‐containing DTBDT derivative can substantially increase the orbital overlap area between adjacent conjugated chains and thus dramatically enhance charge‐carrier mobility up to 0.55 cm² V^?1 s^?1. The outstanding charge‐transport characteristics of this polymer allowed the realization of high‐performance organic solar cells with a power conversion efficiency (PCE) of 5.1 %. Detailed studies on the morphological factors that enable the maximum PCE of the polymer solar cells are discussed along with a hole/electron mobility analysis based on the space‐charge‐limited current model.     

High performance semiconducting polymers containing bis(bithiophenyl dithienothiophene)‐based repeating groups for organic thin film transistors

New dithienothiophene‐containing conjugated polymers, such as poly(2,6‐bis(2‐thiophenyl‐3‐dodecylthiophene‐2‐yl)dithieno[3,2‐b;2′,3′‐d]thiophene, 4 and poly(2,6‐bis (2‐thiophenyl‐4‐dodecylthiophene‐2‐yl)dithieno[3,2‐b;2′,3′‐d]thiophene, 8 have been successfully synthesized via Stille coupling reactions using dodecyl‐substituted thiophene‐based monomers, bistributyltin dithienothiophene, and bistributyltin bithiophene; these polymers have been fully characterized. The main difference between the two polymers is the substitution position of the dodecyl side chains in the repeating group. Grazing‐incidence X‐ray diffraction (GI‐XRD) gave clear evidence of edge‐on orientation of polycrystallites to the substrate. The semiconducting properties of the two polymers have been evaluated in organic thin film transistors (OTFTs). The two conjugated polymers 4 and 8 exhibit fairly high hole carrier mobilities as high as μ_ave = 0.05 cm²/Vs (I_ON/OFF = 3.42 × 10⁴) and μ_ave = 0.01 cm²/Vs, (I_ON/OFF = 1.3 × 10⁵), respectively, after thermal annealing process. The solvent annealed films underwent reorganization of the molecules to induce higher crystallinity. Well‐defined atomic force microscopy (AFM) topography supported a significant improvement in TFT device performance. The hole carrier mobilities of the solvent annealed films are comparable to those obtained for a thermally annealed sample, and were one‐order higher than those obtained with a pristine sample. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

New selenophene‐based low‐band gap conjugated polymers for organic photovoltaics

Low‐band gap selenophene‐based polymers were synthesized. Their optoelectronic and photovoltaic properties and space‐charge limited currents were compared with those of the related thiophene‐based polymers. The band gaps of the Se‐based derivatives were approximately 0.05–0.12 eV lower than those of their thiophene counterparts. Organic photovoltaic (OPV) devices based on the blends of these polymers and 1‐(3‐methoxycarbonyl)propyl‐1‐phenyl‐[6,6]‐C₇₁ (PC₇₁BM) were fabricated, and the maximum power conversion efficiency of the OPV device based on PSPSBT and PC₇₁BM was 3.1%—with a short‐circuit current density (J_sc) of 9.3 mA cm^?2, an open‐circuit voltage (V_oc) of 0.79 V, and a fill factor of 0.42—under AM 1.5 G illumination (100 mW cm^?2). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4550–4557     

Linking polythiophene chains with vinylene‐bridges: A way to improve charge transport in polymer field‐effect transistors

A series of novel branched polythiophene derivatives bearing different densities of vinylene‐bridges as linking chains were synthesized by a general synthetic strategy. The organic field‐effect transistors, which were fabricated by spin‐coating the polymer solutions onto octadecyltrichlorosilane‐modified SiO₂/Si substrates with top‐contact configuration, afforded a high mobility of 8.0 × 10^?3 cm² V^?1 s^?1 with an on/off ratio greater than 10⁴ and a threshold voltage of about ?3 V in saturation regime. The devices based on these polymers possessed better performance than those of polymers without conjugated bridges and polymers with longer conjugated bridges. These results demonstrated that the combination of conjugated polythiophene backbones and vinylene‐bridges would improve the carrier mobility. As an emerging class of conjugated materials, polymers with vinylene‐bridges as linking chains would open up new opportunities in organic electronics, and their applications in organic electronics are promising. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1381–1392, 2009     

ipso‐Arylative Ring‐Opening Polymerization as a Route to Electron‐Deficient Conjugated Polymers

ipso‐Arylative ring‐opening polymerization of 2‐bromo‐8‐aryl‐8H‐indeno[2,1‐b]thiophen‐8‐ol monomers proceeds to M_n up to 9 kg mol^?1 with conversion of the monomer diarylcarbinol groups to pendent conjugated aroylphenyl side chains (2‐benzoylphenyl or 2‐(4‐hexylbenzoyl)phenyl), which influence the optical and electronic properties of the resulting polythiophenes. Poly(3‐(2‐(4‐hexylbenzoyl)phenyl)thiophene) was found to have lower frontier orbital energy levels (HOMO/LUMO=?5.9/?4.0 eV) than poly(3‐hexylthiophene) owing to the electron‐withdrawing ability of the aryl ketone side chains. The electron mobility (ca. 2×10^?3 cm² V^?1 s^?1) for poly(3‐(2‐(4‐hexylbenzoyl)phenyl)thiophene) was found to be significantly higher than the hole mobility (ca. 8×10^?6 cm² V^?1 s^?1), which suggests such polymers are candidates for n‐type organic semiconductors. Density functional theory calculations suggest that backbone distortion resulting from side‐chain steric interactions could be a key factor influencing charge mobilities.     

Diketopyrrolopyrrole?Thiophene‐Based Acceptor–Donor–Acceptor Conjugated Materials for High‐Performance Field‐Effect Transistors

We report the synthesis, morphology, and field‐effect‐transistor (FET) characteristics of new acceptor–donor–acceptor conjugated materials that consist of diketopyrrolopyrrole (DPP) acceptor groups and one of four different thiophene moieties, that is, dithiophene (2T), thieno[3,2‐b]‐thiophene (TT), dithieno[3,2‐b:2′,3′‐d]‐thiophene (DTT), and 5,5′′′‐di‐(2‐ethylhexyl)‐[2,3′;5′,2′′;4′′,2′′′]quaterthiophene (4T). The optical band gaps of the as‐prepared materials are smaller than 1.7 eV, which is attributed to the strong intramolecular charge transfer and the backbone coplanarity of the thiophene moieties. The order of both crystallinity and FET mobility (×10^?2–×10^?4 cm² V^?1 s^?1) is TT2DPP > 4T2DPP > 2T2DPP >DTT2DP, which differ in the structure of the π‐conjugated cores and core symmetry. Well‐ordered intermolecular chain packing was confirmed by the GIXD and AFM results. In particular, the FET hole mobility of TT2DPP was further improved to 0.1 cm² V^?1 s^?1, which was attributed to the well‐interconnected structure through solution‐shearing. These experimental results suggest the potential applications of the new DPP? thiophene? DPP conjugated materials for organic electronic devices.     

The influence of electron deficient unit and interdigitated packing shape of new polythiophene derivatives on organic thin‐film transistors and photovoltaic cells

A series of new polythiophene derivatives containing a thiazole ring as an electron deficient unit were successfully synthesized via Stille coupling reactions. Synthesized polymers were classified into two types (H‐shape packing and A‐shape packing) based on their interdigitated packing structure induced by different side chain configurations. The thiophene derivatives that contained a thiazole unit ( PT50Tz50 , PTz100 , and PTTz ) exhibited much better thermal stability than did the full thiophene polymers ( PT100 and PTT ). The polymers containing the thiazole unit ( PTz100 and PTTz ) showed a red‐shifted absorption spectrum with clear vibronic structure. In addition, the XRD and AFM results showed that the polymers containing the thiazole unit and interdigitated H‐shape exhibited much better ordered and connected intermolecular structures than did other polymers. The improved intermolecular ordering and surface morphologies directly facilitated charge carrier transport in thin film transistor (TFT) devices, without introducing charge traps, and yielded higher solar cell performance. Among these polymers, the PTTz copolymer exhibited the best TFT performance (μ = 0.050 cm² V^?1 s^?1, on/off ratio = 10⁶, and V_th = ?2 V) and solar cell performance (PCE = 1.39%, J_sc = 6.58 mA cm^?2, and V_oc = 0.58 V). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Novel pendent thiophene side‐chained benzodithiophene for polymer solar cells

In this article, pendent thiophene (2‐butyl‐5‐octylthiophene) side chain is used to modify the backbone of the polymers containing benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and thieno[3,4‐c]pyrrole‐4,6‐dione (TPD). Compared with the dodecyloxy side‐chained polymer (P1), pendent thiophene‐based polymers (P2 and P3) show similar number‐average molecular weight (M_n), polydispersity index, thermal stability (T_d ～ 334–337 °C), and optical band gaps ( ) (～1.8 eV). Polymer (P2)‐based BDT with pendent thiophene and ethylhexyl‐modified TPD shows relatively low‐lying HOMO energy level (?5.52 eV) and nearly 1 V high open circuit voltage (V_OC). The polymer solar cell devices based on three copolymers show power conversion efficiencies from 2.01% to 4.13%. The hole mobility of these polymers tested by space charge limited current method range from 3.4 × 10^?4 to 9.2 × 10^?4 cm²V^?1s^?1. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1558–1566     

Thiazolothiazole‐containing polythiophenes with low HOMO level and high hole mobility for polymer solar cells

Two regiochemically defined polythiophenes containing thiazolothiazole acceptor unit were synthesized by palladium(0)‐catalyzed Stille coupling reaction. The thermal, electrochemical, optical, charge transport, and photovoltaic properties of these copolymers were examined. Compared to P1 with head‐to‐head coupling of two middle thiophenes, P2 with head‐to‐tail coupling of two middle thiophenes exhibits 40 nm red shift of absorption spectrum in film and 0.3 eV higher HOMO level. Both polymers exhibit field‐effect hole mobility as high as 0.02 cm² V^?1 s^?1. Polymer solar cells (PSCs) were fabricated based on the blend of the polymers and methanofullerene[6,6]‐phenyl C71‐butyric acid methyl ester (PC₇₁BM). The PSC based on P1 :PC₇₁BM (1:2, w/w) exhibits a power conversion efficiency of 2.7% under AM 1.5, 100 mW cm^?2, two times of that based on P2 :PC₇₁BM. The higher efficiency is attributed to lower HOMO (?5.6 eV) and smaller phase separation scale in P1 :PC₇₁BM blend. Tiny change in thiophene connection of P1 and P2 lead to great difference in HOMO, phase separation scale, and efficiency of their photovoltaic devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Influence of Backbone Chlorination on the Electronic Properties of Diketopyrrolopyrrole (DPP)‐Based Dimers

Chlorination of π‐conjugated backbones is garnering great interest because of fine‐tuning electronic properties of conjugated materials for organic devices. Herein we report a synthesis of thiophene‐based diketopyrrolopyrrole (DPP) dimers and their chlorinated counterparts by introducing a chlorine atom in the outer thiophene ring to investigate the influence of the chlorination on charge transport. The backbone chlorination lowers both the HOMO and the LUMO of the dimers and leads to a blue‐shift of maximum absorption in compared to unsubstituted counterparts. X‐ray analysis reveals that the chlorine atom prompts the outer thiophene ring out of the planarity of the backbone with a relatively large torsional angle. The chlorinated dimers exhibit slipped one‐dimensional packing decorated with multiple intermolecular interactions, because of a combination of a negative inductive effect and a positive mesomeric effect of the halogen atom, which might facilitate charge transport within the oligomeric backbones. The mobility in the single‐crystal OFET devices of the chlorinated dimers is up to 1.5 cm² V^?1 s^?1, which is two times higher than that of the non‐chlorinated DPP dimers. Our results indicate that the chlorine atom plays a key role in directing non‐covalent interactions to lock the slipped stacks, enabling electronic coupling between adjacent molecules for efficient charge transport. In addition, our results also demonstrate that these DPP dimers with straight n‐octyl chains exhibit higher mobilities than the dimers with branched 2‐ethylhexyl chains.     

A Three‐Dimensional Porous Organic Semiconductor Based on Fully sp2‐Hybridized Graphitic Polymer

Dimensionality plays an important role in the charge transport properties of organic semiconductors. Although three‐dimensional semiconductors, such as Si, are common in inorganic materials, imparting electrical conductivity to covalent three‐dimensional organic polymers is challenging. Now, the synthesis of a three‐dimensional π‐conjugated porous organic polymer (3D p‐POP) using catalyst‐free Diels–Alder cycloaddition polymerization followed by acid‐promoted aromatization is presented. With a surface area of 801 m² g^?1, full conjugation throughout the carbon backbone, and an electrical conductivity of 6(2)×10^?4 S cm^?1 upon treatment with I₂ vapor, the 3D p‐POP is the first member of a new class of permanently porous 3D organic semiconductors.     

Anthradithiophene–thiophene copolymers with broad UV–vis absorption for organic solar cells and field‐effect transistors

New semiconducting copolymers, poly((TIPS‐ADT)‐(4,4′‐didodecyl‐2,2′‐bithiophene)) (PTADT2) and poly((TIPS‐ADT)‐(2,2′‐(4,4′‐didodecyl‐2,2′‐bithiophene)dithiophene)) (PTADT4) , produced by incorporating 5,11‐bis(triisopropylsilylethynyl) anthra[2,3‐b:7,6‐b']dithiophene (TIPS‐ADT) and alkyl‐thiophene derivatives were synthesized via Stille coupling polymerization. The optical, electrochemical, structural, field‐effect transistor, and solar cell properties of the polymers were investigated. The polymers showed good solubility at room temperature in common organic solvents due to their abundant side groups including TIPS and dodecyl side chains. Both polymers showed very broad UV absorption spectra covering the spectral range from 300 to 750 nm as a result of the combination of the different absorption ranges of the TIPS‐ADT unit (short wavelength region) and thiophene derivatives (long wavelength region). The FET device fabricated using PTADT4 containing additional unsubstituted thiophene rings as a spacer between TIPS‐ADT and thiophene derivatives showed a higher hole mobility (5.7 × 10^?4 cm²/V s) than the PTADT2 device (2.8 × 10^?5 cm²/V s), due to the improved intermolecular ordering caused by the reduced steric hindrance between bulky side chain groups. In addition, the PTADT4 :(6,6)‐phenyl‐C₇₀‐butyric acid methyl ester (PC₇₀BM) device showed an enhanced power conversion efficiency (PCE) of 1.30% compared with the PTADT2 :PC₇₀BM device (PCE of 0.55%) under AM 1.5G irradiation (100 mW/cm²). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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     

Synthesis and characterization of porphyrin‐based D‐π‐A conjugated polymers for polymer solar cells

Two novel porphyrin‐based D‐A conjugated copolymers, PFTTQP and PBDTTTQP , consisting of accepting quinoxalino[2,3‐b′]porphyrin unit and donating fluorene or benzo[1,2‐b:4,5‐b′]dithiophene unit, were synthesized, respectively via a Pd‐catalyzed Stille‐coupling method. The quinoxalino[2,3‐b′]porphyrin, an edge‐fused porphyrin monomer, was used as a building block of D‐A copolymers, rather than the simple porphyrin unit in conventional porphyrin‐based photovoltaic polymers reported in literature, to enhance the coplanarity and to extend the π‐conjugated system of polymer main chains, and consequently to facilitate the intramolecular charge transfer (ICT). The thermal stability, optical, and electrochemical properties as well as the photovoltaic characteristics of the two polymers were systematically investigated. Both the polymers showed high hole mobility, reaching 4.3 × 10^?4 cm² V^?1 s^?1 for PFTTQP and 2.0 × 10^?4 cm² V^?1 s^?1 for PBDTTTQP . Polymer solar cells (PSCs) made from PFTTQP and PBDTTTQP demonstrated power conversion efficiencies (PCEs) of 2.39% and 1.53%, both of which are among the highest PCE values in the PSCs based on porphyrin‐based conjugated polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013     

Molecular Heterostructures of Covalent Triazine Frameworks for Enhanced Photocatalytic Hydrogen Production

Conjugated polymers have emerged as promising candidates for photocatalytic H₂ production owing to their structural designability and functional diversity. However, the fast recombination of photoexcited electrons and holes limits their H₂ production rates. We have now designed molecular heterostructures of covalent triazine frameworks to facilitate charge‐carrier separation and promote photocatalytic H₂ production. Benzothiadiazole and thiophene moieties were selectively incorporated into the covalent triazine frameworks as electron‐withdrawing and electron‐donating units, respectively, by a sequential polymerization strategy. The resulting hybrids exhibited much improved charge‐carrier‐separation efficiency as evidenced by photophysical and electrochemical characterization. An H₂ evolution rate of 6.6 mmol g^?1 h^?1 was measured for the optimal sample under visible‐light irradiation (λ>420 nm), which is far superior to that of most reported conjugated‐polymer photocatalysts.     

Novel alkoxyanthracene donor and benzothiadiazole acceptor for organic thin film transistor and bulk heterojunction organic photovoltaic cells

Novel alkoxy anthracene (ODA)‐based polymeric semiconductors were designed for polymer solar cell applications. Alkoxyanthracene, which contains many π electrons and electron donating group, was easily synthesized. The copolymers, poly(alkoxy anthracene‐alt‐thiophene benzothiadiazole thiophene) poly(ODA‐TBT) and poly(alkoxy anthracene‐alt‐benzothiadiazole) poly(ODA‐BT), have been obtained by Suzuki coupling polymerization. Both polymers have ODA unit as a donor and benzothiadiazole as an acceptor. ODA‐TBT has thiophene linkages between ODA and benzothiadiazole. The optical, thermal, and electrochemical properties have been investigated by UV–visible absorption, thermal gravimetric analysis, differential scanning calorimetry, and CV. Organic thin‐film transistor using polymers showed that the hole mobility of poly(ODA‐alt‐TBT) was around 3.6 × 10^?3 cm²/Vs with on/off ratio of 9.91 × 10⁵ while that of poly(ODA‐alt‐BT) was around 1.21 × 10^?2 cm²/Vs with on/off ratio of 2.64 × 10⁶. Organic photovoltaic performance based on polymers were evaluated with a configuration of ITO/PEDOT:PSS/active layer/LiF/Al. Poly(ODA‐TBT) exhibits a short circuit current (J_sc) of 3.9 mA/cm² and power conversion efficiency (PCE) of 1.4%, and poly(ODA‐BT) exhibits the J_sc of 6.4 mA/cm² and PCE of 2.2%. The better device performance of poly(ODA‐BT) is attributed to its charge transfer ability and enhanced mobility and crystallinity although poly(ODA‐BT) does not have extended π‐conjugation due to twisted structure compared with poly(ODA‐TBT). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1306–1314     

Board‐like Fused‐Thiophene Liquid Crystals and their Benzene Analogs: Facile Synthesis,Self‐Assembly,p‐Type Semiconductivity,and Photoluminescence

Fused‐thiophene discotic liquid crystals were designed and easily synthesized by Suzuki coupling and FeCl₃ oxidized tandem cyclodehydrogenation reactions, including homo‐ and cross‐coupling reactions. The resulting hexagonal and rectangular columnar mesomorphic supramolecular structures formed were characterized by polarizing optical microscopy, differential scanning calorimetry, and small‐angle X‐ray scattering. The charge carrier transport properties in the mesophases of two of the synthesized fused‐thiophene discogens were measured by transient photocurrent time‐of‐flight (TOF) technique, revealing fast hole transport values in the range of 10^?3 to 10^?2 cm² V^?1 s^?1, thus demonstrating potential applications in electronic devices. The luminescent sanidic mesogens, with different extended π‐conjugated systems, also emit blue, green, or red light, with absolute photoluminescent quantum yields as high as 18 %.     

Molecular Engineering of Conjugated Polybenzothiadiazoles for Enhanced Hydrogen Production by Photosynthesis

The search for metal‐free organic photocatalysts for H₂ production from water using visible light remains a key challenge. Reported herein is a molecular structural design of pure organic photocatalysts, derived from conjugated polybenzothiadiazoles, for photocatalytic H₂ evolution using visible light. By alternating the substitution position of the electron‐withdrawing benzothiadizole unit on the phenyl unit as a comonomer, various polymers with either one‐ or three‐dimensional structures were synthesized and the effect of the molecular structure on their catalytic activity was investigated. Photocatalytic H₂ evolution efficiencies up to 116 μmol h^?1 were observed by employing the linear polymer based on a phenyl‐benzothiadiazole alternating main chain, with an apparent quantum yield (AQY) of 4.01 % at 420 nm using triethanolamine as the sacrificial agent.     

Diketopyrrolopyrrole‐based acceptor–acceptor conjugated polymers: The importance of comonomer on their charge transportation nature

Besides the donor–acceptor (D–A) type, acceptor–acceptor (A–A) polymers are another class of important alternative conjugated copolymers, but have been less studied in the past. In this study, two kinds of A–A polymers, P1 and P2 , have been designed and synthesized based on diketopyrrolopyrrole in combination with the second electron‐deficient unit, perylenediimide or thieno[3,4‐c]pyrrole‐4,6‐dione. UV–vis absorption spectroscopy revealed that these two kinds of polymers have a band gap of 1.28–1.33 eV. Their highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels are around ?5.6 and ?4.0 eV for P1 polymers, whereas ?5.4 and ?3.7 eV for P2 polymers, respectively. Density functional theory study disclosed that P1 backbone is in a vastly twisting state, whereas that of P2 is completely planar. Furthermore, organic field‐effect transistor devices were fabricated using these two kinds of polymers as the active material. Of interest, the devices based on P1 polymers displayed n‐channel behaviors with an electron mobility in the order of 10^?4 cm² V^?1 s^?1. In contrast, the P2 ‐based devices exhibited only p‐channel charge transportation characteristics with a hole mobility in the order of 10^?3 cm² V^?1 s^?1. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2356–2366     

Diazaisoindigo bithiophene and terthiophene copolymers for application in field‐effect transistors and solar cells

Two donor–acceptor conjugated polymers with azaisoindigo as acceptor units and bithiophene and terthiophene as donor units have been synthesized by Stille polymerization. These two polymers have been successfully applied in field‐effect transistors and polymer solar cells. By changing the donor component of the conjugated polymer backbone from bithiophene to terthiophene, the density of thiophene in the backbone is increased, manifesting as a decrease in both ionization potential and in electron affinity. Therefore, the charge transport in field‐effect transistors switches from ambipolar to predominantly hole transport behavior. PAIIDTT exhibits hole mobility up to 0.40 cm²/Vs and electron mobility of 0.02 cm²/Vs, whereas PAIIDTTT exhibits hole mobility of 0.62 cm²/Vs. Polymer solar cells were fabricated based on these two polymers as donors with PC₆₁BM and PC₇₁BM as acceptor where PAIIDTT shows a modest efficiency of 2.57% with a very low energy loss of 0.55 eV, while PAIIDTTT shows a higher efficiency of 6.16% with a higher energy loss of 0.74 eV. Our results suggest that azaisoindgo is a useful building block for the development of efficient polymer solar cells with further improvement possibility by tuning the alternative units on the polymer backbone. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2691–2699