Donor–acceptor photovoltaic polymers based on 1,4‐dithienyl‐2,5‐dialkoxybenzene with intramolecular noncovalent interactions

Donor–acceptor (D–A) conjugated polymers bearing non‐covalent configurationally locked backbones have a high potential to be good photovoltaic materials. Since 1,4‐dithienyl‐2,5‐dialkoxybenzene ( TBT ) is a typical moiety possessing intramolecular S…O interactions and thus a restricted planar configuration, it was used in this work as an electron‐donating unit to combine with the following electron‐accepting units: 3‐fluorothieno[3,4‐b]thiophene ( TFT ), thieno‐[3,4‐c]pyrrole‐4,6‐dione ( TPD ), and diketopyrrolopyrrole ( DPP ) for the construction of such D–A conjugated polymers. Therefore, the so‐designed three polymers, PTBTTFT , PTBTTPD , and PTBTDPP , were synthesized and investigated on their basic optoelectronic properties in detail. Moreover, using [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as acceptor material, polymer solar cells (PSCs) were fabricated for studying photovoltaic performances of these polymers. It was found that the optimized PTBTTPD cell gave the best performance with a power conversion efficiency (PCE) of 4.49%, while that of PTBTTFT displayed the poorest one (PCE = 1.96%). The good photovoltaic behaviors of PTBTTPD come from its lowest‐lying energy level of the highest occupied molecular orbital (HOMO) among the three polymers, and good hole mobility and favorable morphology for its PC₇₁BM‐blended film. Although PTBTDPP displayed the widest absorption spectrum, the largest hole mobility, and regular chain packing structure when blended with PC₇₁BM, its unmatched HOMO energy level and disfavored blend film morphology finally limited its solar cell performance to a moderate level (PCE: 3.91%). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 689–698     

Ethynylene‐containing donor–acceptor alternating conjugated polymers: Synthesis and photovoltaic properties

Four ethynylene‐containing donor‐acceptor alternating conjugated polymers P1 – P4 with 2,5‐bis(dodecyloxy) substituted phenylene or carbazole as the donor unit and benzothiadiazole (BTZ) as the acceptor unit were synthesized and used as donor polymers in bulk heterojunction polymer solar cells. The optical, electrochemical, and photovoltaic properties of these four polymers with the ethylene unit located at different positions of the polymer chains were systematically investigated. Our results demonstrated that absorption spectra and the HOMO and LUMO energy levels of polymers could be tuned by varying the position of the ethynylene unit in the polymer chains. Photovoltaic devices based on polymer/PC₇₁BM blend films spin coated from chloroform and dichlorobenzene solutions were investigated. For all four polymers, open circuit voltages (V_oc) higher than 0.8 V were obtained. P4 , with ethynylene unit between BTZ and thiophene, shows the best performance among these four polymers, with a V_oc of 0.94 V, a J_sc of 4.2 mA/cm², an FF of 0.40, and a PCE of 1.6%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Novel two‐dimensional donor–acceptor conjugated polymers containing quinoxaline units: Synthesis,characterization, and photovoltaic properties

Novel two‐dimensional donor–acceptor (D–A) structured conjugated polymers, P1–P4, were designed and synthesized by introducing electron‐deficient quinoxaline as core and electron‐rich alkoxyl‐phenylenevinylene in side chains and p‐phenylenevinylene, triphenylamine, or thiophene in main chain. Benefited from the D–A structures, the polymers possess low bandgaps of 1.75 eV, 1.86 eV, 1.59 eV, and 1.58 eV for P1, P2, P3, and P4, respectively, and show broad absorption band in the visible region: the shorter wavelength absorption peak at ～400 nm ascribed to the conjugated side chains and the longer wavelength absorption peak between 500 nm and 750 nm belonging to the absorption of the conjugated main chains. Especially, the absorption band of P4 film covers the whole visible range from 300 nm to 784 nm. The power conversion efficiencies of the polymer solar cells based on P1–P4 as donor and PCBM as acceptor are 0.029%, 0.14%, 0.46%, and 0.57%, respectively, under the illumination of AM 1.5, 100 mW/cm². The polymers with the low bandgap and broad absorption band are promising photovoltaic materials. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4038–4049, 2008     

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     

Intramolecular donor–acceptor copolymers containing side‐chain‐tethered perylenebis(dicarboximide) moieties for panchromatic solar cells

A series of side‐chain‐tethered copolymers containing the N‐(2‐ethylhexyl)‐N′‐(thiophene‐3‐yl)‐3,4:9,10‐perylenebis(dicarboximide) (thiophene‐PDI) moieties and 4,4‐diethylhexyl‐cyclopenta[2,1‐b:3,4‐b′]dithiophene unit were synthesized via Grignard metathesis polymerizations. With the incorporation of pendent perylenebis(dicarboximide) (PDI) moieties as acceptor side chains and thiophene as the donor backbone, the copolymers exhibited the intramolecular donor–acceptor characteristic and displayed a panchromatic absorption ranging from 290 to 1100 nm and ideal bandgaps of 1.49 to 1.52 eV. Due to the coplanarity of PDI moieties, the charge separation and transfer process were more effective and enhanced after photoexcitation. When increased the weight ratio of PC₆₁BM:polymer to 3, the J_sc could be raised significantly. The value of bandgap decreased slightly, and both V_oc and J_sc showed an upward trend with the increase of molar ratio of thiophene‐PDI unit from 50% (the copolymer P11) to 75% (the copolymer P13). The polymer/PC₆₁BM devices have shown a significant improvement from 0.45 to 1.66% with a judicious modulation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1978–1988     

Electrochemical and optical properties of novel donor‐acceptor thiophene‐perylene‐thiophene polymers

In this study, donor‐acceptor type thiophene‐perylene‐thiophene monomers were synthesized and polymerized by both oxidative polymerization using FeCl₃ as catalyst and the electrochemical process. UV–vis, FTIR, ¹H NMR, and elemental analysis techniques were used for structural characterization. Thermal behaviors of these compounds were determined by using TGA system. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels and electrochemical and optical band gap values were calculated by using the results of cyclic voltammetry and UV–vis measurements, respectively. The number–average molecular weight (M_n), weight–average molecular weight (M_w), and polydispersity index (PDI) values of synthesized polymers were determined by size exclusion chromatography. Conductivity measurements of these polymers were carried out by electrometer by using a four‐point probe technique. The conductivity was observed to be increased by iodine doping. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1974–1989, 2008     

Synthesis,optical, and electrochemical properties of novel copolymers on the basis of benzothiadiazole and electron‐rich arene units

Novel alternating conjugated copolymers ( P1–P6 ) consisting of an electron‐deficient benzothiadiazole and a variety of electron‐rich thiophene‐arene‐thiophene units were synthesized by palladium‐catalyzed polycondensations (Stille and Suzuki reactions), aiming at processable materials with a reduced optical band gap. The structures of P1–P6 were confirmed by ¹H NMR and ¹³C NMR, and their molecular weights were determined by size exclusion chromatography. In the Suzuki polycondensation, the role of the catalyst [Pd(PPh₃)₄ and Pd(OAc)₂] on the resulting molecular weight was investigated. Pd(OAc)₂ enhances the molecular weight of the polymers for both thiophene and phenylene bis‐boronic esters as compared with Pd(PPh₃)₄. The optical properties of the polymers were examined in solution and the solid state. The polymers with n‐octyl substituents ( P1 , P4 , P5 , and P6 ) on the thiophene rings possessed less‐planar structures as a result of torsional steric hindrance, and their absorption spectra appeared blueshifted as compared with their unsubstituted analogues ( P2 and P3 ). The electrochemical properties of the polymers were studied using cyclic voltammetry. Although the alkyl substitution affects the oxidation potential, only marginal differences in the reduction potentials were observed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2360–2372, 2002     

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     

Jacket‐like structure of donor–acceptor chromophores‐based conducting polymers for photovoltaic cell applications

Through the Stille coupling polymerization, a series of soluble acceptor/donor quinoxaline/thiophene alternating conducting polymers with a hole‐transporting moiety of carbazole as a side chain ( PCPQT ) has been designed, synthesized, and investigated. The UV–vis measurement of the charge‐transferred type PCPQT s of different molecular weights with low polydispersity exhibits a red shifting of their absorption maximum from 530 to 630 nm with increasing chain length (M_n: from 1100 to 19,200). The HOMO and LUMO energy levels of PCPQT can be determined from the cyclic voltammetry measurement to be ?5.36 and ?3.59 eV, respectively. Solar cells made from PCPQT/PCBM bulk heterojunction show a high open‐circuit voltage, V_oc of ～0.75 V, which is significantly higher than that of a solar cell made from conventional poly(3‐hexyl thiophene)/ PCBM as the active polymer PCPQT has lower HOMO level. Further improvements are anticipated through a rational design of the new low band‐gap and the structurally two‐dimensional donor–acceptor conducting polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1607–1616, 2010     

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,characterizations, and electrochromic properties of donor–acceptor type polymers containing 2, 1, 3‐benzothiadiazole and different thiophene donors

Three donor–acceptor type π‐conjugated monomers containing 2, 1, 3‐benzothiadiazole (Tz) as the acceptor unit and different thiophene derivatives (thiophene, 3,4‐ethylenedioxythiophene, and thieno[3,2‐b]thiophene) as the donor units have been synthesized via Stille coupling reaction. The corresponding polymers are electrochemically deposited onto FTO glass by cyclic voltammetry (CV). The maximum absorption wavelength of the neutral polymers varies with the electron‐rich character of incorporated thiophene moieties, giving rise to tunable colors. In addition, the prepared polymer films demonstrate reasonable transmittance modulation, fast switching rate, high color efficiency and good stability, which meet the requirements of smart windows and electrochromic display applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2239–2246     

Thieno[3,2‐b]thiophene‐substituted benzodithiophene in donor–acceptor type semiconducting copolymers: A feasible approach to improve performances of organic photovoltaic cells

Thieno[3,2‐b]thiophene‐substituted benzo[1,2‐b:4,5‐b′]dithiophene donor units (TTBDT) serve as novel promising building blocks for donor–acceptor (D‐A) copolymers in organic photovoltaic cells. In this study, a new D‐A type copolymer (PTTBDT‐TPD) consisting of TTBDT and thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) is synthesized by Stille coupling polymerization. A PTTBDT‐TPD analog consisting of TTBDT and alkylthienyl‐substituted BDT (PTBDT‐TPD) is also synthesized to compare the optical, electrochemical, morphological, and photovoltaic properties of the polymers. Bulk heterojunction photovoltaic devices are fabricated using the polymers as p‐type donors and [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM) as the n‐type acceptor. The power conversion efficiencies of the devices fabricated using PTTBDT‐TPD and PTBDT‐TPD are 6.03 and 5.44%, respectively. The difference in efficiency is attributed to the broad UV–visible absorption and high crystallinity of PTTBDT‐TPD. The replacement of the alkylthienyl moiety with thieno[3,2‐b]thiophene on BDT can yield broad UV–visible absorption due to extended π‐conjugation, and enhanced molecular ordering and orientation for organic photovoltaic cells. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3608–3616     

One donor–two acceptor (D–A1)‐(D–A2) random terpolymers containing perylene diimide,naphthalene diimide,and carbazole units

A series of one donor–two acceptor (D–A₁)‐(D–A₂) random terpolymers containing a 2,7‐carbazole donor and varying compositions of perylene diimide (PDI) and naphthalene diimide (NDI) acceptors was synthesized via Suzuki coupling polymerization. The optical properties of the terpolymers are weighted sums of the constituent parent copolymers and all show strong absorption over the 400 to 700 nm range with optical bandgaps ranging from 1.77 to 1.87 eV, depending on acceptor composition. The copolymers were tested as acceptor materials in bulk heterojunction all‐polymer solar cells using poly[(4,8‐bis‐(2‐ethylhexyloxy)‐benzo[1,2‐b;4,5‐b′]dithiophene)‐2,6‐diyl‐alt‐(4‐(2‐ethylhexanoyl)‐thieno[3,4‐b]thiophene)‐2,6‐diyl] (PBDTTT‐C) as the donor material. In contrast to the optoelectronic properties, the measured device parameters are not composition dependent, and rather depend solely on the presence of the NDI unit, where the devices containing any amount of NDI perform half as well as those using the parent polymer containing only carbazole and PDI. Overall this is the first example of a one donor–two acceptor random terpolymer system containing perylene diimide (PDI) and naphthalene diimide (NDI) acceptor units, and demonstrates a facile method of tuning polymer optoelectronic properties while minimizing the need for complicated synthetic and purification steps. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3337–3345     

Synthesis and photovoltaic properties of conjugated copolymers based on benzimidazole and various thiophene

A new accepter unit, dimethyl‐2H‐benzimidazole, was prepared and used for the synthesis of the conjugated polymers containing electron donor–acceptor pair for organic photovoltaics (OPVs). Dimethyl‐2H‐benzimidazole unit was designed to substitute the BT unit of poly(N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)) (PCDTBT). A series of new semiconducting polymers with 2,2‐dimethyl‐2H‐benzimidazole, 9‐heptadecanyl‐9H‐carbazole, and thiophene (or bithiophene) units was synthesized using Stille polymerization to generate PCDTMBIs (or PCBBTMBIs). In dimethyl‐2H‐benzimidazole, the sulfur at 2‐position of BT unit was replaced with dialkyl substituted carbon, while keeping the 1,2‐quinoid form, to improve the solubility of the polymers. The absorption spectra of PCDTMBIs with thiophene units exhibit two maximum peaks at about 430 and 613–645 nm in solution. The solutions of PCBBTMBIs show two absorption peaks at about 445–456 and 630–645 nm which is red‐shifted about 20 nm when compared with PCDTMBIs caused by the introduction of bithiophene units. In most efficient polymer PCBBTMBI3, the device annealed at 100 °C for 10 min demonstrated a V_OC value of 0.60 V, a J_SC value of 4.31 mA/cm², and a FF of 0.35, leading to the power conversion efficiency (PCE) of 0.91%, under white light illumination (AM 1.5 G and 100 mW/cm²). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of isoindigo‐based polymers using CH‐arylation polycondensation reactions for organic photovoltaics

A series of three new low bandgap donor–acceptor–donor–acceptor^/ (D–A–D–A^/) polymers have been successfully synthesized based on the combination of isoindigo as the electron‐deficient acceptor and 3,4‐ethylenedioxythiophene as the electron‐rich donor, followed by CH‐arylation with different acceptors (4,7‐dibromo[c][1,2,5]‐(oxa, thia, and/or selena)diazole ( 4a‐c )). These polymers were used as donor materials for photovoltaic applications. All of the polymers are highly stable and show good solubility in chlorinated solvents. The highest power conversion efficiency of 1.6% was achieved in the bulk heterojunction photovoltaic device that consisted of poly ((E)?6‐(7‐(benzo‐[c][1,2,5]‐thiadiazol‐4‐yl)?2,3‐dihydrothieno‐[3,4‐b][1,4]dioxin‐5‐yl)?6′‐(2,3‐dihydrothieno‐[3,4‐b][1,4]‐dioxin‐5‐yl)?1,1′‐bis‐(2‐octyldodecyl)‐[3,3′‐biindolinylidene]‐2,2′‐dione) as the donor and PC₆₁BM as the acceptor, with a short‐circuit current density (J_sc) of 8.10 mA/cm², an open circuit voltage (V_oc) of 0.56 V and a fill factor of 35%, which indicates that these polymers are promising donors for polymer solar cell applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2926–2933     

Synthesis,characterization, and solar cell and transistor applications of phenanthro[1,2‐b:8,7‐b′]dithiophene–Diketopyrrolopyrrole semiconducting polymers

Synthesis, characterization, and polymer solar cell and transistor application of a series of phenanthro[1,2‐b:8,7‐b′]dithiophene‐based donor–acceptor (D–A)‐type semiconducting polymers combined with a diketopyrrolopyrrole unit are reported. The present polymers showed some unique features such as strong aggregation behavior, high thermal stability, and short π–π stacking distance (3.5–3.6 Å), which are suitable for high performance organic materials. In addition, they have a significantly extended absorption up to 1000 nm with a band gap of ca. 1.2 eV. However, such strong intermolecular interaction reduced their solubility and molecular weights, which resulted in low crystalline nature and moderate field‐effect mobility of 0.01 cm² V^?1 s^?1. Furthermore, such strong aggregation behavior led to the large‐scale phase separation in the blend films, which may prevent the effective photocurrent generation, limiting J_sc and power conversion efficiency of 2.0%. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 709–718     

A Pentacyclic Nitrogen‐Bridged Thienyl–Phenylene–Thienyl Arene for Donor–Acceptor Copolymers: Synthesis,Characterization, and Applications in Field‐Effect Transistors and Polymer Solar Cells

A pentacyclic benzodipyrrolothiophene ( BDPT ) unit, in which two outer thiophene rings are covalently fastened with the central phenylene ring by nitrogen bridges, was synthesized. The two pyrrole units embedded in BDPT were constructed by using one‐pot palladium‐catalyzed amination. The coplanar stannylated Sn‐BDPT building block was copolymerized with electron‐deficient thieno[3,4‐c]pyrrole‐4,6‐dione ( TPD ), benzothiadiazole ( BT ), and dithienyl‐diketopyrrolopyrrole ( DPP ) acceptors by Stille polymerization. The bridging nitrogen atoms make the BDPT motif highly electron‐abundant and structurally coplanar, which allows for tailoring the optical and electronic properties of the resultant polymers. Strong photoinduced charge‐transfer with significant band‐broadening in the solid state and relatively higher oxidation potential are characteristic of the BDPT‐based polymers. Poly(benzodipyrrolothiophene‐alt‐benzothiadiazole) ( PBDPTBT ) achieved the highest field‐effect hole mobility of up to 0.02 cm² V^?1 s^?1. The photovoltaic device using the PBDPTBT /PC₇₁BM blend (1:3, w/w) exhibited a V_oc of 0.6 V, a J_sc of 10.34 mA cm^?2, and a FF of 50 %, leading to a decent PCE of 3.08 %. Encouragingly, the device incorporating poly(benzodipyrrolothiophene‐alt‐thienopyrrolodione) ( PBDPTTPD )/PC₇₁BM (1:3, w/w) composite delivered a highest PCE of 3.72 %. The enhanced performance arises from the lower‐lying HOMO value of PBDPTTPD to yield a higher V_oc of 0.72 V.     

Donor–acceptor‐integrated conjugated polymers based on carbazole[3,4‐c:5,6‐c]bis[1,2,5]thiadiazole with tight π–π stacking for photovoltaics

An original strategy to construct a new donor–acceptor (D–A)‐integrated structure by directly imposing “pull” unit on the “push” moiety to form fused ring architecture has been developed, and poly{N‐alkyl‐carbazole[3,4‐c:5,6‐c]bis[1,2,5]thiadiazole‐alt‐thiophene} (PCBTT) with D–A‐integrated structure, in which two 1,2,5‐thiadiazole rings are fixed on carbazole in 3‐, 4‐ and 5‐, 6‐position symmetrically and thiophene is used as bridge, has been synthesized. The interaction between pull and push units has fine tuned the HOMO/LUMO energy levels, and the resulting copolymer covers the solar flux from 300 to 750 nm. The interaction between pull and push units is worth noting that due to the fused five rings inducing strong intermolecular interaction, an extremely short π–π stacking distance of 0.32 nm has been achieved for PCBTT both in powder and solid states. This is the shortest π–π stacking distance reported for conjugated polymers. Additionally, an obvious intramolecular charge transfer and energy transfer from donor units to acceptor units have been detected in this D–A integration. A moderate‐to‐high open‐circuit voltage of ～0.7 V in PCBTT:[6,6]‐phenyl‐C61 butyric acid methyl ester (PCBM) (w/w = 1/2) solar cells is achieved due to the low‐lying HOMO energy level of PCBTT. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of bithiazole‐based crystalline polymers via palladium‐catalyzed direct CH arylation

Palladium‐catalyzed direct arylation polycondensation afforded a bithiazole‐based homopolymer and donor–acceptor (D–A)‐type copolymers where the bithiazole unit served as an acceptor unit. The results of polymerization strongly depended on the solubility of the polymers; long alkyl chain substituents were required for the formation of high‐molecular‐weight polymers in high yields owing to low solubility of the bithiazole‐based polymers. X‐ray diffraction studies revealed that the obtained polymers were highly crystalline. In particular, a well‐ordered lamellar structure was observed in the D–A‐type copolymer with flexible alkyl chains after thermal annealing, presumably owing to the combination of interchain interactions between the bithiazole units and the electrostatic D–A interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1396–1402     

Acceptor–acceptor conjugated copolymers based on perylenediimide and benzothiadiazole for all‐polymer solar cells

Donor–acceptor (D–A) conjugated copolymers are one of known classes of organic optoelectronic materials and have been well developed. However, less attention has been paid on acceptor–acceptor (A–A) conjugated analogs. In this work, two types of A–A conjugated copolymers, namely P1‐Cn and P2‐Cn (n is the carbon number of their alkyl side chains), were designed and synthesized based on perylenediimide ( PDI ) and 2,1,3‐benzothiadiazole ( BT ). Different from P1‐Cn , P2‐Cn polymers have additional acetylene π‐spacers between PDI and BT and thus hold a more planar backbone configuration. Property studies revealed that P2‐Cn polymers possess a much red‐extended UV–vis absorption spectrum, stronger π–π interchain interactions, and one‐order larger electron mobility in their neat film state than P1‐Cn . However, all‐polymer solar cells using P1‐Cn as acceptor component and poly(3‐hexyl thiophene) or poly(2,7‐(9,9‐didodecyl‐fluoene)‐alt?5,5′‐(4,7‐dithienyl‐2‐yl‐2,1,3‐benzothiadiazole) as donor component exhibited much better performance than those based on P2‐Cn . Apart from their backbone chemical structure, the side chains were found to have little influence on the photophysical, electrochemical, and photovoltaic properties for both P1‐Cn and P2‐Cn polymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1200–1215