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     

Two‐Step direct arylation for synthesis of naphthalenediimide‐based conjugated polymer

A naphthalenediimide (NDI)‐based conjugated polymer was synthesized by a two‐step direct C‐H arylation sequence. In the first step, two ethylenedioxythiophene units were coupled to NDI by direct arylation. In the second step, the direct arylation polycondensation of the monomer, formed in the first step, with 2,7‐dibromo‐9,9‐dioctylfluorene afforded the corresponding NDI‐based conjugated polymer ( PEDOTNDIF ) with molecular weight of 21,500 in 91% yield. The optical and electrochemical properties of the polymer were evaluated. The polymer showed ambipolar behavior in organic field‐effect transistors (OFETs). The electron mobility of PEDOTNDIF was estimated to be 2.3 × 10^?6 cm² V^?1 s^?1 using an OFET device with source‐drain (S‐D) Au electrodes. A modified OFET device with S‐D MgAg electrodes increased the electron mobility for PEDOTNDIF to 1.0 × 10^?5 cm² V^?1 s^?1 due to the more suitable work function of these electrodes, which reduced the injection barrier to the semiconducting polymer. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1401–1407     

Synthesis and characterization of a new ethynyl‐linked alternating anthracene/fluorene copolymer for organic thin film transistor

A new p‐type conjugated copolymer, poly(9,10‐diethynylanthracene‐alt‐9,9‐didodecylfluorene) (PDADF), which is composed of ethynyl‐linked alternating anthracene/fluorene, is synthesized via a palladium(II)‐catalyzed Sonogashira coupling reaction with 9,10‐diethynylanthracene and 2,7‐diiodo‐9,9‐didodecyl‐fluorene. The obtained polymer is confirmed by FTIR, ¹H‐NMR, ¹³C‐NMR and elemental analysis. The PDADF had very good solubility in organic solvents such as chloroform and had a weight average molecular weight of 29,300 with a polydispersity index of 1.29. The PL maximum of the polymer was found at 533 and 568 nm for a solution and 608 nm for film, respectively. The highest occupied molecular orbital (HOMO) energy of the polymer is ?5.62 eV as measured via cyclic voltammetry (CV). A solution‐processed thin film transistor device showed a carrier mobility value of 6.0 × 10^?4 cm²/Vs with a threshold voltage of ?17 V and a capacitance (C_i) of 10 nF/cm². The out‐of‐plane and in‐plane GIXD pattern of spin‐coated polymer on SiO₂ dielectric surfaces showed an amorphous halo near 2θ = 20°. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1609–1616, 2009     

Polymer solar cells based on quinoxaline and dialkylthienyl substituted benzodithiophene with enhanced open circuit voltage

A poly[benzodithiophene‐alt‐di‐2‐thienyl‐quinoxaline] series (PBDTDPQ‐EH, PBDTDPQ‐OD, and PBDTDPQ‐HDT) was synthesized via Stille coupling. Deep highest occupied molecular orbital (HOMO) levels were achieved by the introduction of 2‐decyl‐4‐hexyl‐thiophen‐yl (HDT) side chains. The introduction of the various side chains increased the molecular weight of the polymers, and the polymers dissolved well in common organic solvents at room temperature. The HOMO energy level (?5.20 to ?5.49 eV) decreased because of the 2D conjugated structure. X‐ray diffraction analysis showed that PBDTDPQ‐OD had a slightly edge‐on structure. In the case of PBDTDPQ‐HDT, however, the structure was amorphous due to the thiophene side chain, and the extent of π stacking increased. After fabricating bulk‐heterojunction‐type polymer solar cells, the OPV characteristics were evaluated. The values of open‐circuit voltage (V_oc), short‐circuit current (J_sc), fill factor, and power conversion efficiency (PCE) were 0.88 V, 7.9 mA cm^?2, 45.4%, and 3.2%, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1028–1036     

Synthesis and characterization of low‐bandgap cyclopentadithiophene‐biselenophene copolymer and its use in field‐effect transistor and polymer solar cells

Novel series of conjugated copolymers, incorporating cyclopentadithiophene (CPDT) and the biselenophene ( R‐CPDT‐Se2 ), were synthesized by Pd‐catalyzed Stille coupling polymerization. The optical, electrochemical, field‐effect carrier mobilities, and photovoltaic properties of the R‐CPDT‐Se2 were investigated and compared with cyclopentadithiophene (CPDT) and the bithiophene ( EHex‐CPDT‐T2 ). The highest hole mobility of thin film transistor devices fabricated with new p‐type polymer semiconductors, Oct‐CPDT‐Se2 , was 1.3 × 10^?3 cm²/Vs with an on/off ratio of about 10⁵. The maximum power conversion efficiency of polymer solar cell fabricated with the blend of EHex‐CPDT‐Se2 /C₇₁‐PCBM reached 1.86% with an open circuit voltage (V_OC) of 0.55 V, a short circuit current density (J_sc) of 7.27 mA/cm², and a fill factor (FF) of 0.47 under AM 1.5G irradiation (100 mW/cm²). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Novel triarylamine‐based alternating conjugated polymer with high hole mobility: Synthesis,electro‐optical,and electronic properties

Novel bi‐triphenylamine‐containing aromatic dibromide M3 , N,N‐bis(4‐bromophenyl)‐N′,N′‐dipheny‐l,4‐phenylenediamine, was successfully synthesized. The novel conjugated polymer P1 having number‐average molecular weight of 1.31 × 10⁴ was prepared via Suzuki coupling from the dibromide M3 and 9,9‐dioctylfluorene‐2,7‐diboronic acid bis(1,3‐propanediol) ester. Polymer P1 had excellent thermal stability associated with a high glass‐transition temperature (T_g = 141 °C). The hole‐transporting and UV‐vis‐near‐infrared electrochromic properties were examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the conjugated polymer films cast onto indium‐tin oxide‐coated glass substrates exhibited two reversible oxidation redox couples at E_1/2 values of 0.73 and 1.13 V versus Ag/Ag⁺ in acetonitrile solution. The hole mobility of the conjugated polymer P1 revealed ～10^?3 cm² V^?1 s^?1, which is much higher than that of other conjugated polymer systems. The observed UV‐vis‐near‐infrared absorption change in the conjugated polymer film P1 at applied potentials ranging from 0.00 to 1.23 V are fully reversible and associated with strong color changes from pale yellowish in its neutral form to green and blue in its oxidized form. Using a combination of experimental study and theoretical investigation, we proposed an oxidation mechanism based on molecular orbital theory, which explains the cyclic voltammetry experimental results well. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

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     

Design and synthesis of dithieno[3,2‐b:2′3′‐d]pyrrole‐based conjugated polymers for photovoltaic applications: consensus between low bandgap and low HOMO energy level

A strategy of the fine‐tuning of the degree of intrachain charge transfer and aromaticity of polymer backbone was adopted to design and synthesize new polymers applicable in photovoltaics. Three conjugated polymers P1 , P2 , and P3 were synthesized by alternating the electron‐donating dithieno[3,2‐b:2′3′‐d]pyrrole (D) and three different electron‐accepting (A) segments ( P1 : N‐(2‐ethylhexyl)phthalimide; P2 : 1,4‐diketo‐3,6‐diphenylpyrrolo[3,4‐c]pyrrole; and P3 : thiophene‐3‐hexyl formate) in the polymer main chain. Among the three polymers, P2 possessed the broadest absorption band ranging from 300 to 760 nm, the lowest bandgap (1.63 eV), and enough low HOMO energy level (?5.27 eV) because of the strong intrachain charge transfer from D to A units and the appropriate extent of quinoid state in the main chain of P2 , which was convinced by the theoretical simulation of molecular geometry and front orbits. Photovoltaic study of solar cells based on the blends of P1 – P3 and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) demonstrated that P2 :PCBM exhibited the best performance: a power conversion efficiency of 1.22% with a high open‐circuit voltage (V_OC) of 0.70 V and a large short‐circuit current (I_SC) of 5.02 mA/cm² were achieved. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

Synthesis and properties of the conjugated polymers with indenoindene and benzimidazole units for organic photovoltaics

A new electron deficient unit, dimethyl‐2H‐benzimidazole (MBI), and dihydroindeno[2,1‐a]indene (ININE) moiety as electron‐rich unit were coupled to synthesize the conjugated polymers containing electron donor–acceptor pair for organic photovoltaics. ININE, MBI, and thiophene (or bithiophene) units were incorporated using Stille and Suzuki polymerization to generate poly(2,7‐(5,5,10,10‐tetrakis(2‐ethylhexyl)‐5,10‐dihydro‐ indeno[2,1‐a]indene)‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2,2‐dimethyl‐2H‐benzimidazole)) (PININEDTMBIs) (or PININEBBTMBIs). In MBI, the sulfur at 2‐position of 2,1,3‐benzothiadiazole (BT) unit was replaced with dialkyl‐substituted carbon, whereas keeping the 1,2‐quinoid form, to improve the solubility of the polymers. The field‐effect hole mobility of PININEBBTMBI was 3.2 × 10^?4 cm²/Vs which was improved as compared to that of PININEDTMBI (2.7 × 10^?5 cm²/Vs) caused by the introduction of bithiophene units. In case of the most efficient polymer, PININEBBTMBI, the device with the configuration of indium tin oxide (ITO)/poly(3,4‐ethylenedioxythiophene) (PEDOT):polystyrene sulfonate (PSS)/polymer:PC₇₁BM(1:4 w/w)/Al, annealed at 100 °C for 10 min demonstrated a open circuit voltage of 0.78 V, a short‐circuit current density of 6.66 mA/cm², and a fill factor of 0.41, leading to the power conversion efficiency of 2.11%, under white‐light illumination (AM 1.5 G, 100 mW/cm²). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and photovoltaic properties of two‐dimensional D‐A copolymers with conjugated side chains

Four novel two‐dimensional (2D) donor–acceptor (D‐A) type copolymers with different conjugated side chains, P1 , P2 , P3 , and P4 (see Fig. 1 ), are designed and synthesized for the application as donor materials in polymer solar cells (PSCs). To the best of our knowledge, there were few reports to systematically study such 2D polymers with D‐A type main chains in this area. The optical energy band gaps are about 2.0 eV for P1 – P3 and 1.67 eV for P4 . PSC devices using P1 – P4 as donor and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester as acceptor in a weight ratio of 1:3 were fabricated and characterized to investigate the photovoltaic properties of the polymers. Under AM 1.5 G, 100 mA/cm² illumination, a high open‐circuit voltage (V_oc) of 0.9 V was recorded for P3 ‐based device due to its low HOMO level, and moderate fill factor was obtained with the best value of 58.6% for P4 ‐based device, which may mainly be the result of the high hole mobility of the polymers (up to 1.82 × 10^?3 cm²/V s). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Organic Thin Film Transistors Based on 2,3‐Dimethylpentacene and 2,3‐Dimethyltetracene

2,3‐Dimethylpentacene (DMP) and 2,3‐dimethyltetracene (DMT) were synthesized, characterized and employed as the channel material in the fabrication of thin‐film transistors. The two methyl groups increase the chemical stability of the compounds versus the pristine acene analogues. The crystals maintain herringbone‐like molecular packing, whereas the weak dipole associated with the unsymmetrical molecule induces an anti‐parallel alignment among the neighbors. This structural motif favors layered film growth on SiO₂/Si surface. Thin film transistors prepared on SiO₂/Si and n‐nonyltrichlorosilane‐modified SiO₂/Si at different substrate temperatures were compared. DMP‐based transistors prepared on rubbed n‐nonyltrichlorosilane‐modified SiO₂/Si substrate gave the highest field‐effect mobility of 0.46 cm²/Vs, whereas DMT‐based transistor gave a mobility of 0.028 cm²/Vs.     

Effect of branched alkyl side chains on the performance of thin‐film transistors and photovoltaic cells fabricated with isoindigo‐based conjugated polymers

New isoindigo and di(thienyl)ethylene‐containing π‐extended conjugated polymers with different branched side chains were synthesized to investigate their physical properties and device performance in thin‐film transistors and photovoltaic cells. 11‐Butyltricosane (S3) and 11‐heptyltricosane (S6) groups were used as side‐chain moieties tethered to isoindigo units. The linking groups between the polymer backbone and bifurcation point in the branched side chain differ in the two polymers (i.e., PIDTE‐S3 and PIDTE‐S6 ). The polymers bearing S6 side chains showed much better charge transport behavior than those with S3 side chains. Thermally annealed PIDTE‐S6 film exhibited an outstanding hole mobility of 4.07 cm² V^?1 s^?1 under ambient conditions. Furthermore, bulk heterojunction organic photovoltaic cells made from a blend film of PIDTE‐S3 and (6,6)‐phenyl C61‐butyric acid methyl ester demonstrated promising device performance with a power conversion efficiency in the range of 4.9–5.0%. © 2015 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 2015 , 53, 1226–1234     

An acceptor‐acceptor conjugated copolymer based on perylene diimide for high mobility n‐channel transistor in air

A new solution‐processable acceptor‐acceptor conjugated copolymer ( P1 ) based on perylene diimide (PDI) incorporating planar electron‐deficient fluorenone was synthesized by palladium(0)‐catalyzed Suzuki coupling reaction. Relative to the donor‐acceptor conjugated copolymer ( P2 ) of PDI and dithienothiophene, polymer P1 exhibits 0.1 eV down shift of lowest unoccupied molecular orbital (LUMO) level, 70 nm blue shift of low‐energy absorption band, and 0.36 eV increase of optical band gap. Polymer P1 in top‐contact bottom‐gate organic field‐effect transistors exhibits a saturation electron mobility of 0.01 cm²/(V s) in air, while P2 does not function in the same device in air. The better air stability of P1 is attributed to a more dense packing of the polymer chains excluding oxygen or water and lower LUMO level of P1 . © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Supramolecular complexes of poly(3‐Hexylthiophene)‐block (and random)‐poly[3‐(2‐(6‐carboxyhexyl)methyl)thiophene] copolymers with perylene bisimide

Block and random copolymers of poly(3‐hexylthiophene) and poly[3‐(2‐(6‐carboxyhexyl)methyl)thiophene] with side‐chain carboxylic functionality ((P3HT‐b‐P3COOH) and (P3HT‐r‐P3COOH) were developed by Grignard Metathesis (GRIM) polymerization. The carboxylic functionality was introduced in the side chain via the oxazoline route. Both the block and random polythiophene copolymers were complexed with pyridine functionalized perylene bisimide to obtain supramolecular block and random polymer complexes. The complex formation in both systems was confirmed by ¹H NMR, WXRD and SAXS studies. An expansion of d spacing upon complex formation was observed in both the block and random copolymer, which could be traced by WXRD. Hole and electron mobilities measured for the supramolecular complexes indicated values which were higher by an order of magnitude for the supramolecular block complex (μ_h ≈ 2.9 × 10⁻⁴ cm²/Vs; μ_e ≈ 3.1 × 10⁻⁶ cm²/Vs) as compared to the random (μ_h ≈ 1.4 × 10⁻⁵ cm²/Vs; μ_e ≈ 4.7 × 10⁻⁷ cm²/Vs) copolymer. These results are indicative of the higher degree of disorder prevailing in the films of random copolymer system compared to the block copolymer. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1574–1583     

Synthesis,characterization, and field‐effect transistor performance of poly[2,6‐bis(3‐tridecanoxythiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]dithiophene]

A new copolymer of benzo[1,2‐b:4,5‐b′]dithiophene and 3,3′‐bis(tridecanoxy)‐5,5′‐bithiophene was synthesized through Stille copolymerization. The bis‐(3‐alkoxythiophene) monomer was synthesized through a silver fluoride mediated, palladium‐catalyzed cross‐coupling, in which bromide functional groups were preserved instead of consumed. The copolymer has been characterized and applied in field‐effect transistors, giving a hole mobility of 2 × 10^?3 cm²/Vs and an on/off ratio >10⁶, with negligible hysteresis, on standard silicon substrates. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1973–1978, 2010     

Synthesis and properties of polythiophenes with conjugated side‐chains containing carbon–carbon double and triple bonds

Two soluble side‐chain conjugated polythiophenes, poly{3‐[2‐(4‐octyloxy‐phenyl)‐vinyl]‐thiophene} (P3OPVT) and poly{3‐(4‐octyloxy‐phenylethynyl)‐thiophene} (P3OPET) have been synthesized successfully. In P3OPVT and P3OPET, substituted benzene rings are connected with the polythiophene backbone through trans carbon–carbon double bond and carbon–carbon triple bond, respectively. Absorption spectra of the P3OPVT and P3OPET both show two absorption peaks located in UV and visible region, respectively. The results of optical and electrochemical measurements indicate that the conjugated side‐chains can reduce the bandgap effectively. This type of side‐chain conjugated polythiophenes may be promising for the applications in polymer photovoltaic cells and field effect transistors. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2206–2214, 2006     

Effects of substituted side‐chain position on donor–acceptor conjugated copolymers

The optical properties and electrical properties of a series of low‐band‐gap conjugated copolymers, in which alkyl side chains were substituted at various positions, were investigated using donor–acceptor conjugated copolymers consisting of a cyclopentadithiophene derivative and dithienyl‐benzothiadiazole. With substituted side chains, the intrinsic properties of the copolymers were significantly altered by perturbations of the intramolecular charge transfer. The absorption of poly[2, 6‐(4,4‐bis(2‐octyl)‐4H‐cyclopenta‐[2,1‐b:3,4‐b′]dithiophene)‐alt‐4, 7‐bis(4‐octyl‐thiophene‐2‐yl)benzo‐2,1,3‐thiadiazole] [ PCPDT‐ttOTBTOT ( P2 )], which assumed a tail–tail configuration, tended to blue shift relative to the absorption of poly[2,6‐(4,4‐bis(2‐octyl)‐4H‐cyclopenta‐[2,1‐b:3,4‐b′]dithiophene)‐alt‐4,7‐bis (thiophene‐2‐yl)benzo‐2,1,3‐thiadiazole] [ PCPDT‐TBTT ( P1 )]. The absorption of poly[2,6‐(4,4‐bis(2‐octyl)‐4H‐cyclopenta‐[2,1‐b:3, 4‐b′]dithiophene)‐alt‐4,7‐bis(3‐octyl‐thiophene‐2‐yl)benzo‐2,1,3‐thiadiazole] [ PCPDT‐hhOTBTOT ( P3 )], which assumed a head–head configuration, was blue shifted relative to that of P2 . The electrical transport properties of field‐effect transistors were sensitive to the side chain position. The field‐effect mobility in P2 (μ₂ = 1.8 × 10^?3 cm²/V s) was slightly lower than that in P1 (μ₁ = 4.9 × 10^?3 cm²/V s). However, the mobility of P3 was very low (μ₃ = 3.8 × 10^?6 cm²/V s). Photoexcitation spectroscopy showed that the charge generation efficiency (shown in transient absorption spectra) and polaron pair mobility in P1 and P2 were higher than in P3 , yielding P1 and P2 device performances that were better than the performance of devices based on P3 . © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Poly(3‐hexylthiophene)‐b‐poly(3‐cyclohexylthiophene): Synthesis,microphase separation,thin film transistors,and photovoltaic applications

We report the synthesis, characterization, microphase separation, field‐effect charge transport, and photovoltaic properties of regioregular poly(3‐hexylthiophene)‐b‐poly(3‐cyclohexylthiophene) (P3HT‐b‐P3cHT). Two compositions of P3HT‐b‐P3cHT (HcH63 and HcH77) were synthesized with weight‐average molecular weights of 155,500 and 210,800 and polydispersity indices of 1.45 and 1.57, respectively. Solvent‐casted HcH77 was found to self‐assemble into nanowires with a width of 12.5 ± 0.9 nm and aspect ratios of 50–120, as observed by TEM imaging. HcH77 and HcH63 annealed 280 °C were observed by small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) to be microphase‐separated with characteristic length scales of 17.0–21.7 nm. The microphase‐separated domains were shown to be crystalline with interlayer backbone (100) d‐spacings of 1.69 and 1.40 nm, which correspond to the P3HT and P3cHT blocks, respectively. Field‐effect transistors fabricated from P3HT‐b‐P3cHT thin films showed a mobility of holes (0.0019 cm²/Vs) which is independent of thermal annealing. Bulk heterojunction solar cells based on HcH77/fullerene (PC₇₁BM) blend thin films had a maximum power conversion efficiency of 2.45% under 100 mW/cm² AM1.5 solar illumination in air. These results demonstrate that all‐conjugated block copolymers are suitable semiconductors for applications in field‐effect transistors and bulk heterojunction solar cells. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 614–626, 2010     

Copolymers of fluorene and thiophene with conjugated side chain for polymer solar cells: Effect of pendant acceptors

Two copolymers of fluorene and thiophene with conjugated side‐chain pending acceptor end group of cyanoacetate ( P2 ) and malononitrile ( P3 ) were synthesized. Both polymers exhibit good thermal stability and low highest occupied molecular orbital level (?5.5 eV). In comparison with P2 , P3 exhibits stronger UV–vis absorption and higher hole mobility. Polymer solar cells based on P3 :PC₇₁BM exhibits a power conversion efficiency of 1.33% under AM 1.5, 100 mW/cm², which is three times of that based on P2 :PC₇₁BM. The higher efficiency is attributed to better absorption, higher hole mobility, and the reduced phase separation scale in P3 :PC₇₁BM blend. The aggregate domain size in P3 :PC₇₁BM blend is 50 nm, much smaller than that in P2 :PC₇₁BM blend (200 nm). Tiny difference in the end groups on side chains of P2 and P3 leads to great difference in phase separation scale, charge transport, and efficiency of their photovoltaic devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011