Efficient organic photovoltaic cells based on thiazolothiazole and benzodithiophene copolymers with π‐conjugated bridges

New donor–π–acceptor (D–π–A) type conjugated copolymers, poly[(4,8‐bis((2‐hexyldecyl)oxy)benzo[1,2‐b:4,5‐b′]dithiophene)‐alt‐(2,5‐bis(4‐octylthiophen‐2‐yl)thiazolo[5,4‐d]thiazole)] (PBDT‐tTz), and poly[(4,8‐bis((2‐hexyldecyl)oxy)benzo[1,2‐b:4,5‐b′]dithiophene)‐alt‐(2,5‐bis(6‐octylthieno[3,2‐b]thiophen‐2‐yl)thiazolo[5,4‐d]thiazole)] (PBDT‐ttTz) were synthesized and characterized with the aim of investigating their potential applicability to organic photovoltaic active materials. While copolymer PBDT‐tTz showed a zigzagged non‐linear structure by thiophene π‐bridges, PBDT‐ttTz had a linear molecular structure with thieno[3,2‐b]thiophene π‐bridges. The optical, electrochemical, morphological, and photovoltaic properties of PBDT‐tTz and PBDT‐ttTz were systematically investigated. Furthermore, bulk heterojunction photovoltaic devices were fabricated by using the synthesized polymers as p‐type donors and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester as an n‐type acceptor. PBDT‐ttTz showed a high power conversion efficiency (PCE) of 5.21% as a result of the extended conjugation arising from the thienothiophene π‐bridges and enhanced molecular ordering in the film state, while PBDT‐tTz showed a relatively lower PCE of 2.92% under AM 1.5 G illumination (100 mW/cm²). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1978–1988     

Synthesis and photovoltaic investigation of dithieno[2,3‐d:2′,3′‐d′]‐benzo[1,2‐b:3,4‐b′:5,6‐d″]trithiophene‐based conjugated polymer with an enlarged π‐conjugated system

Compared with benzo[1,2‐b:3,4‐b′:5,6‐d″]trithiophene (BTT), an extended π‐conjugation fused ring derivative, dithieno[2,3‐d:2′,3′‐d′]benzo[1,2‐b:3,4‐b′:5,6‐d″]trithiophene (DTBTT) has been designed and synthesized successfully. For investigating the effect of extending conjugation, two wide‐bandgap (WBG) benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based conjugated polymers (CPs), PBDT‐DTBTT, and PBDT‐BTT, which were coupled between alkylthienyl‐substituted benzo[1,2‐b:4,5‐b′]dithiophene bistin (BDT‐TSn) and the weaker electron‐deficient dibromides DTBTTBr₂ and BTTBr₂ bearing alkylacyl group, were prepared. The comparison result revealed that the extending of conjugated length and enlarging of conjugated planarity in DTBTT unit endowed the polymer with a wider and stronger absorption, more ordered molecular structure, more planar and larger molecular configuration, and thus higher hole mobility in spite of raised highest occupied molecular orbital (HOMO) energy level. The best photovoltaic devices exhibited that PBDT‐DTBTT/PC₇₁BM showed the power conversion efficiency (PCE) of 2.73% with an open‐circuit voltage (V_OC) of 0.82 V, short‐circuit current density (J_SC) of 6.29 mA cm^?2, and fill factor (FF) of 52.45%, whereas control PBDT‐BTT/PC₇₁BM exhibited a PCE of 1.98% under the same experimental conditions. The 38% enhanced PCE was mainly benefited from improved absorption, and enhanced hole mobility after the conjugated system was extended from BTT to DTBTT. Therefore, our results demonstrated that extending the π‐conjugated system of donor polymer backbone was an effective strategy of tuning optical electronic property and promoting the photovoltaic property in design of WBG donor materials.     

Effects of alkyl side chain length of low bandgap naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole‐based copolymers on the optoelectronic properties of polymer solar cells

Two donor‐π‐acceptor (D‐π‐A) type naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole (NT)‐based conjugated copolymers (CPs), namely, PBDT‐TT‐DTNT‐HD and PBDT‐TT‐DTNT‐OD, containing different side chain length (2‐hexyldecyl, HD and 2‐octyldodecyl, OD) anchoring to thiophene π‐bridge between the two‐dimensional (2D) 5‐((2‐butyloctyl)thieno[3,2‐b]thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT‐TT) unit and NT moiety are developed and fully characterized. The resultant two copolymers exhibited broader absorption in wide range of 300–820 nm and obviously deepened E_HOMO of approximately −5.50 eV. The effects of side chain length on film‐forming ability, absorption, energy levels, aggregation, dielectric constant (ɛ_r), mobility, morphology, and photovoltaic properties are further systematically investigated. It was found that the side chain length had little impact on solution‐processability, absorption, energy levels, and aggregation in CB solution of resultant CPs. However, tinily increasing side chain length promoted to form the more ordered structure of neat polymer film even if the corresponding ɛ_r decreased. As a result, the side‐chain‐extended PBDT‐TT‐DTNT‐OD:PC₇₁BM‐based device achieved 32% increased FF than that of PBDT‐TT‐DTNT‐HD:PC₇₁BM and thus the PCE was significantly raised from 3.99% to 5.21%, which were benefited from 2 times higher SCLC hole mobility, more favorable phase separation, and improved exciton dissociation. These findings could provide an important and valuable insight by side chain modulation for achieving efficient PSCs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2059–2071     

A two-dimension medium band gap conjugated polymer based on 5,10-bis(alkylthien-2-yl)dithieno[3,2-d:3′,2′-d′]benzo[1,2-b:4,5-b′]dithiophene: Synthesis and photovoltaic application

A two-dimension medium band gap copolymer poly{5,10-bis(4,5-didecylthien-2-yl)dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene-2,7-diyl-alt-2,5-di(3-octylthien-2-yl) thiophen-5,5′-diyl}, named as PDTBDT-T-3T, was prepared by the palladium-catalyzed Stille cross coupling reaction and characterized. The resulting polymer exhibits good solubility in common organic solvents, excellent thermal stability, and extensive light absorption from 300 nm to 650 nm with an optical band gap of 1.92 eV, the highest occupied molecular orbital (HOMO) level of ?5.03 eV and the hole mobility up to 1.92 × 10^?4 cm²·V^?1·s^?1. The power conversion efficiencies (PCEs) of 2.02%–3.19% have been achieved in the traditional PVCs for the copolymer. It should be noted that the PCEs of 4.2% for the inverted PVCs from the copolymer with PFN (poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl- fluorene)]) as cathode modifying interlayer, were similar with the PCEs of 4.39% for the inverted PVCs from P3HT:PC₇₁BM at the same condition. These results indicated that the copolymer could be used as potential candidate for P3HT.     

Effects of donor unit and π‐bridge on photovoltaic properties of D–A copolymers based on benzo[1,2‐b:4,5‐c']‐dithiophene‐4,8‐dione acceptor unit

A series of donor‐π‐acceptor (D‐π‐A) conjugated copolymers ( PBDT‐AT, PDTS‐AT, PBDT‐TT , and PDTS‐TT ), based on benzo[1,2‐b:4,5‐c']dithiophene‐4,8‐dione (BDD) acceptor unit with benzodithiophene (BDT) or dithienosilole (DTS) as donor unit, alkylthiophene (AT) or thieno[3,2‐b]thiophene (TT) as conjugated π‐bridge, were designed and synthesized for application as donor materials in polymer solar cells (PSCs). Effects of the donor unit and π‐bridge on the optical and electrochemical properties, hole mobilities, and photovoltaic performance of the D‐π‐A copolymers were investigated. PSCs with the polymers as donor and PC₇₀BM as acceptor exhibit an initial power conversion efficiency (PCE) of 5.46% for PBDT‐AT , 2.62% for PDTS‐AT , 0.82% for PBDT‐TT , and 2.38% for PDTS‐TT . After methanol treatment, the PCE was increased up to 5.91%, 3.06%, 1.45%, and 2.45% for PBDT‐AT, PDTS‐AT, PBDT‐TT , and PDTS‐TT , respectively, with significantly increased FF. The effects of methanol treatment on the photovoltaic performance of the PSCs can be ascribed to the increased and balanced carrier transport and the formation of better nanoscaled interpenetrating network in the active layer. The results indicate that both donor unit and π‐bridge are crucial in designing a D‐π‐A copolymer for high‐performance photovoltaic materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1929–1940     

Synthesis and photovoltaic performances of benzo[1,2‐b:4,5‐b']dithiophene‐alt‐2,3‐diphenylquinoxaline copolymers pending functional groups in phenyl rings

Two donor/acceptor (D/A)‐based benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐2,3‐biphenyl quinoxaline copolymers of P 1 and P 2 were synthesized pending different functional groups (thiophene or triphenylamine) in the 4‐positions of phenyl rings. Their thermal, photophysical, electrochemical, and photovoltaic properties, as well as morphology of their blending films were investigated. The poly(4,8‐bis((2‐ethyl‐hexyl)oxy)benzo[1,2‐b:4,5‐b'] dithiophene)‐alt‐(2,3‐bis(4′‐bis(N,N‐bis(4‐(octyloxy) phenylamino)‐ 1,1′‐biphen‐4‐yl)quinoxaline) ( P 2) exhibited better photovoltaic performance than poly(4,8‐bis((2‐ethylhexyl)oxy)benzo[1,2‐b:4,5‐b'] dithiophene)‐alt‐(2,3‐bis(4‐(5‐octylthiophen‐2‐yl)phenyl)quinoxaline) ( P 1) in the bulk‐heterojunction polymer solar cells with a configuration of ITO/PEDOT:PSS/polymers: [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM)/LiF/Al. A power conversion efficiency of 3.43%, an open‐circuit voltage of 0.80 V, and a short‐circuit current of 9.20 mA cm^?2 were achieved in the P 2‐based cell under the illumination of AM 1.5, 100 mW cm^?2. Importantly, this power conversion efficiency level is 2.29 times higher than that in the P 1‐based cell. Our work indicated that incorporating triphenylamine pendant in the D/A‐based polymers can greatly improved the photovoltaic properties for its resulting polymers.     

Synthesis and photovoltaic properties of copolymers based on benzo[1,2‐b:4,5‐b′]dithiophene and thiophene with electron‐withdrawing side chains

Six alternating conjugated copolymers ( PL1 – PL6 ) of benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and thiophene, containing electron‐withdrawing oxadiazole (OXD), ester, or alkyl as side chains, were synthesized by Stille coupling reaction. The structures of the polymers were confirmed, and their thermal, optical, electrochemical, and photovoltaic properties were investigated. The introduction of conjugated electron‐withdrawing OXD or formate ester side chain benefits to decrease the bandgaps of the polymers and improve the photovoltaic performance due to the low steric hindrance of BDT. Bulk heterojunction polymer solar cells (PSCs) were fabricated based on the blend of the as‐synthesized polymers and the fullerene derivative [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) in a 1:2 weight ratio. The maximum power conversion efficiency of 2.06% was obtained for PL5 ‐based PSC under the illumination of AM 1.5, 100 mW/cm². © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Benzo[1,2-b:4,5-b′]dithiophene-based conjugated polyelectrolyte for the cathode modification of inverted polymer solar cells

A conjugated polyelectrolyte (CPE) named PBNBr, is prepared by post-quaternizing of poly{4,8-bis(octyloxy)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-9,9-bis(3′-((N,N-dimethylamino)propyl)fluorene-2,7-diyl} (PBN) with bromoethane. The chemical strucutes, electrooptical properties of the PBNBr is fully characterized. As compared with the PBN, the PBNBr exhibit much better methanol solution processibility, and more effectively tuning ability for the work function (W_f) of ITO (W_F bare ITO, ?4.8 eV, W_F of ITO with PBN interlayer, ?4.1 eV, W_F of ITO with PBNBr interlayer ?3.9 eV). The open circuit voltages (V_OC) and power conversion efficiencies (PCEs) of polymer solar cells from the blend film of poly(3-hexylthiophene) (P3HT) and [6,6]-phenylC₆₁-butyric acid methyl ester (PC₆₁BM) with PBN and/or PBNBr modified ITO as cathode are respectively increased about 27% and 120% in contrast to those for the control devices with bare ITO as cathode. And PCEs of 4.21% and 4.53% are achieved in the PSCs with PBN and/or PBNBr modified ITO as cathode.     

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     

Low‐bandgap quinoxaline‐based D–A‐type copolymers: Synthesis,characterization, and photovoltaic properties

Three classes of quinoxaline (Qx)‐based donor–acceptor (D–A)‐type copolymers, poly[thiophene‐2,5‐diyl‐alt‐2,3‐bis(4‐(octyloxy)phenyl‐quinoxaline‐5,8‐diyl] P(T‐Qx), poly{4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐2,3‐bis(4‐(octyloxy)phenyl‐quinoxaline‐5,8‐diy} P(BDT‐Qx), and poly{4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(5′,8′‐di‐2‐thienyl‐2,3‐bis(4‐octyloxyl)phenyl)‐quinoxaline‐5,5‐diyl} P(BDT‐DTQx), were synthesized via a Stille coupling reaction. The Qx unit was functionalized at the 2‐ and 3‐positions with 4‐(octyloxy)phenyl to provide good solubility and to reduce the steric hindrance. The absorption spectra of the Qx‐containing copolymers could be tuned by incorporating three different electron‐donating moieties. Among these, P(T‐Qx) acted as an electron donor and yielded a high‐performance solar cell by assuming a rigid planar structure, confirmed by differential scanning calorimetry, UV–vis spectrophotometer, and density functional theory study. In contrast, the P(BDT‐Qx)‐based solar cell displayed a lower power conversion efficiency (PCE) with a large torsional angle (34.7°) between the BDT and Qx units. The BDT unit in the P(BDT‐DTQx) backbone acted as a linker and interfered with the formation of charge complexes or quinoidal electronic conformations in a polymer chain. The PCEs of the polymer solar cells based on these copolymers, in combination with [6,6]‐phenyl C70 butyric acid methyl ester (PC₇₁BM), were 3.3% [P(T‐Qx)], 1.9% [P(BDT‐Qx)], and 2.3% [P(BDT‐DTQx)], respectively, under AM 1.5G illumination (100 mW cm^?2). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

A low bandgap polymer based on isoindigo and bis(dialkylthienyl)benzodithiophene for organic photovoltaic applications

A new conjugated polymer PBDTT‐ID based on N‐alkylated isoindigo (ID) and bis(2,3‐dialkylthienyl)‐substituted benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) as repeating units was synthesized. It had an optical bandgap of 1.56 eV and a highest occupied molecular orbital (HOMO) energy level of ?5.71 eV. The optical, electrochemical, and photovoltaic properties of new polymer were compared with previous reported polymer PBDT‐ID , which was based on bis(alkoxy)‐substituted benzo[1,2‐b:4,5‐b′]dithiophene. The new polymer displayed lower HOMO energy level and better absorption properties than polymer PBDT‐ID . The solar cells fabricated with PBDTT‐ID /PC₆₁BM (1:2, w/w) blends as active layers exhibited photoresponse in the range of 300–800 nm. A power conversion efficiency of 4.02% and an open circuit voltage (V_oc) of 0.94 V were achieved in polymer solar cell device based on the new polymer. This was the highest V_oc realized among the isoindigo‐based polymers. The relatively high performances of new polymer in solar cell devices were interpreted in terms of material properties and morphologies of polymer/PCBM blends. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and optoelectronic properties of novel benzodifuran semiconducting polymers

Two new semiconducting polymers poly{4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]difuran} ( P1 ) and poly {4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]difuran‐alt‐4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]dithiophene} ( P2 ) have been synthesized. These polymers were tested in bulk heterojunction solar cells yielding power conversion efficiencies of 1.19% for P1 and 0.79% for P2 . The surface morphology of the solar cell devices indicated that both the polymers display a granular morphology with smoother films displaying higher power conversion efficiencies. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Comprehensive study of pyrido[3,4‐b]pyrazine‐based D–π–a copolymer for efficient polymer solar cells

Two D–π–A copolymers, based on the benzo[1,2‐b:4,5‐b′]‐dithiophene (BDT) as a donor unit and benzo‐quinoxaline (BQ) or pyrido‐quinoxaline (PQ) analog as an acceptor (PBDT‐TBQ and PBDT‐TPQ), were designed and synthesized as a p‐type material for bulk heterojunction (BHJ) photovoltaic cells. When compared with the PBDT‐TBQ polymer, PBDT‐TPQ exhibits stronger intramolecular charge transfer, showing a broad absorption coverage at the red region and narrower optical bandgap of 1.69 eV with a relatively low‐lying HOMO energy level at ?5.24 eV. The experimental data show that the exciton dissociation efficiency of PBDT‐TPQ:PC₇₁BM blend is better than that in the PBDT‐TBQ:PC₇₁BM blend, which can explain that the IPCE spectra of the PBDT‐TPQ‐based solar cell were higher than that of the PBDT‐TBQ‐based solar cell. The maximum efficiency of PBDT‐TPQ‐based device reaches 4.40% which is much higher than 2.45% of PBDT‐TBQ, indicating that PQ unit is a promising electron‐acceptor moiety for BHJ solar cells. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1822–1833     

Large branched alkylthienyl bridged naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole-containing low bandgap copolymers: Synthesis and photovoltaic application

Two donor-acceptor (D-A) type low bandgap (LBG) alternating conjugated copolymers containing larger conjugation planarity and stronger electro-withdrawing ability naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT) unit, namely, poly[4,8-bis(5-(n-octylthio)thien-2-yl)-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-4,9-bis(4-(2-decyltetradecyl)thien-2-yl)naphtho- [1,2-c:5,6-c′]bis[1,2,5]thiadiazole-5,5′-diyl] (PBDT-TS-DTNT-DT) and poly[4,8-bis(triiso-propylsilylethynyl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-4,9-bis(4-(2-decyltetradecyl)-thien-2-yl)naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole-5,5′-diyl] (PBDT-TIPS-DTNT-DT), were prepared by the palladium-catalyzed Stille polycondensation and characterized by gel permeation chromatography (GPC), UV-Vis absorption, thermal gravimetric analysis (TGA), cyclic voltammetry (CV) etc. PBDT-TS-DTNT-DT and PBDT-TIPS-DTNT-DT show the broader absorption and deeper highest occupied molecular orbital (HOMO) energy level approximately ?5.45 and ?5.62 eV, respectively. Bulk-heterojuction solar cells based on the resulted polymers and [6,6] phenyl-C₆₁ butyric acid methyl ester (PC₆₁BM) blends, with the device configuration of ITO/PFN/polymer:PC₆₁BM/MoO₃/Ag were prepared and investigated. The results showed the power conversion efficiency (PCE) of 2.67% for PBDT-TS-DTNT-DT/PC₆₁BM (w:w, 1:2) and 0.64% for PBDT-TIPS-DTNT-DT/PC₆₁BM (w:w, 1:1), with relatively high open-circuit voltage (V_OC) of 0.86 and 1.05 V, small short-circuit current (J_SC) of 5.41 and 0.97 mA cm^?2 and moderate fill factor (FF) of 57.8% and 62.4%, under an AM1.5 simulator (100 mWcm^?2), respectively.     

Effect of Fluorination on the Photovoltaic Properties of Medium Bandgap Polymers for Polymer Solar Cells

Fluorination of conjugated polymers is one of the effective strategies to tune the molecular energy levels and morphology for high efficient polymer solar cells (PSCs). Herein, two novel donor‐acceptor conjugated polymers, PffBT and PBT, based on bis(3,5‐bis(hexyloxy)phenyl)benzo[1,2‐ b:4,5‐b']dithiophene and benzo[c][1,2,5]thiadiazole (BT) with or without fluorination, respectively, were synthesized, and their photovoltaic properties were compared. The polymer PffBT based on fluorinated BT showed lower frontier energy levels, improved polymer ordering, and a well‐developed fibril structure in the blend with PC₇₁BM. As a result, the PSCs based on PffBT/PC₇₁BM exhibit a superior power conversion efficiency (PCE) of 8.6% versus 4.4% for PBT‐based devices, due to a high space charge limit current (SCLC) hole mobility, mixed orientation of polymer crystals in the active layer, and low bimolecular recombination.     

Synthesis and characterization of highly conjugated side‐group‐substituted benzo[1,2‐b:4,5‐b′]dithiophene‐based copolymer for use in organic solar cells

A new donor–acceptor (D–A) conjugated copolymer based on benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) was synthesized via a Stille cross‐coupling reaction. A highly conjugated thiophene‐based side group, tris(thienylenevinylene) (TTV), was incorporated into each BDT unit to generate the two‐dimensional D–A copolymer (PBDT‐TTV). An alkoxy‐substituted BDT‐based TPD copolymer (PBDT‐OR) was synthesized using the same polymerization method for comparison. PBDT‐TTV thin films produced two distinct absorption peaks. The shorter wavelength absorption (458 nm) was attributed to the BDT units containing the TTV group, and the longer wavelength band (567–616 nm) was attributed to intramolecular charge transfer between the BDT donor and the TPD acceptor. The highest occupied molecular orbital energy levels of PBDT‐OR and PBDT‐TTV were calculated to be −5.53 and −5.61 eV, respectively. PBDT‐TTV thin films harvested a broad solar spectrum covering the range 300–700 nm. A comparison with the PBDT‐OR films revealed stronger interchain π–π interactions in the PBDT‐TTV films and, thus, a higher hole mobility. A polymer solar cell device prepared using PBDT‐TTV as the active layer was found to exhibit a higher power conversion efficiency than a device prepared using PBDT‐OR under AM 1.5 G (100 mW/cm²) conditions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 653–660     

Palladium-Catalyzed C-H Bond Functionalization of Benzo[1,2-b : 4,5-b′]dithiophene-4,8-dione: A One Step Access to 2-Arylbenzo[1,2-b : 4,5-b′]dithiophene-4,8-diones

The reactivity of benzo[1,2-b : 4,5-b′]dithiophene-4,8-dione in Pd-catalyzed C−H arylation was investigated. Using aryl bromides as aryl source in the presence of carbonate bases in 1,4-dioxane, the mono-C2-arylated benzo[1,2-b : 4,5-b′]dithiophene-4,8-diones were regioselectively obtained. This procedure allowed to introduce both electron-rich and electron-poor aryl substituents on the benzo[1,2-b : 4,5-b′]dithiophene-4,8-dione unit. These conditions were also effective for the coupling with 1-bromonaphthalene, 9-bromophenanthrene as well as aryl bromides bearing synthetically useful nitrile, chloro and methoxy substituents. The photophysical properties of representative arylated compounds have been performed by joint experimental and theoretical studies.     

Donor–acceptor‐structured naphtodithiophene‐based copolymers for organic thin‐film transistors

New donor–acceptor (D‐A) polymers, poly(4,5‐bis(2‐octyldodecyloxy)naphto[2,1‐b:3,4‐b']dithiophenebenzo[c][1,2,5]thiadiazole) (PNDT‐B) and poly(4,5‐bis(2‐octyldodecyloxy)naphto [2,1‐b:3,4‐b′]dithiophene‐4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole) (PNDT‐TBT), with the extended π‐electron delocalization of naphtho[2,1‐b:3,4‐b']dithiophene, were successfully synthesized by Suzuki and Stille coupling reactions. The structure and physical properties of polymers were characterized by DFT calculation, UV–vis absorption, cyclovoltammetry, TGA and DSC analyses. X‐ray diffraction studies indicated a relatively highly ordered intermolecular structure in PNDT‐TBT after annealing. This high degree of molecular order resulted from the crystallinity and increasing planarity, provided by the thiophene linker groups and the interdigitation of the long alkoxy side chains. The new D‐A polymer, PNDT‐TBT, exhibited a p‐type carrier mobility of 0.028 cm²/Vs and an on/off ratio of 5.9 × 10³. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 525–531     

Synthesis and Properties of N,N′‐Bis(difuroxano [3,4‐b:3′,4′‐d]phenyl)oxalic Amide

N,N′‐Bis(difuroxano[3,4‐b:3′,4′‐d]phenyl)oxalic amide was synthesized via acylation, nitration, azidation, and pyrolysis‐denitrogenation from the starting materials of oxalyl chloride and 3,5‐dichloroaniline, under mild reaction conditions, with the yields of 81.0%, 82.0%, 86.0% and 81.7% respectively. The title compound and its precursors were characterized by ¹H NMR, IR, MS, and elemental analysis. The title compound has a density of 1.92 g·cm^?3 by a suspension method, a standard formation enthalpy of 979 kJ·mol^?1 calculated by Gaussian programs, a detonation velocity of 8.17 km·s^?1, and a detonation pressure of 31 GPa obtained by Kamlet Equation. The thermal decomposition reactions of the title compound at different heating rates were tested by differential scanning calorimetry (DSC). The kinetics parameters of the pyrolysis of the compound were calculated by Kissinger's method. The values of apparent activation energy (E_a) and pre‐exponential constant (A) were 226.7 kJ·mol^?1 and 10^23.17 s^?1 respectively. It was presupposed that N,N′‐bis(difuroxano[3,4‐b:3′,4′‐d]phenyl)oxalic amide would be a promising high energetic explosive with low sensitivity.