Open circuit voltage increase by substituted spacer and thieno[3,4-c]pyrrole-4,6-dione for polymer solar cells

We reported on two donor polymers containing thieno[3,4-c]pyrrole-4,6-dione(TPD) derivatives as electron withdrawing units for organic photovoltaics (OPVs). To control molecular weight and solubility of polymers, hexyl side chains are inserted to thiophene spacers. Due to the electron donating characteristic of hexyl side chains, highest occupied molecular orbital (HOMO) energy level of polymer is decreased as 0.18 eV, whereas the open circuit voltage is increased to 1.08 V. When bulk heterojunction devices were fabricated, the best PCE value of 0.360% (V_OC = 0.89 V, J_SC = 1.2 mA/cm², FF = 36.3%) under 100 mW/cm² irradiation.     

Opto-electrical and density functional theory analysis of poly(2,7-carbazole-alt-thieno[3,4-c]pyrrole-4,6-dione) and photovoltaic behaviors of bulk heterojunction structure

To increase open-circuit voltage (V_oc), we introduced thieno[3,4-c]pyrrole-4,6-dione (TPD) moieties which has unsubstituted and substituted thiophene spacers. Poly(2,7-carbazole-alt-TPD) derivatives, namely PCDTTPD and PCDHTTPD, were copolymerized with 2,7-carbazole through Suzuki coupling reaction. An increase in the molecular weight and a decrease in the highest occupied molecular orbital (HOMO) energy level are confirmed. Steric hindrance caused by rotational dynamics was measured by density functional theory calculation. When the resulting polymers, PCDHTTPD, were used to fabricate a bulk heterojunction device with PC₇₁BM, V_oc increased to 0.84 V, whereas the short-circuit current density (J_sc) decreased to 0.93 mA/cm² because of poor charge dissociation.     

Cross-linked polymers based on 2,3,5,6-tetra-substituted pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP): Synthesis, optical and electronic properties

A series of 2,3,5,6-tetra-substituted pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP) derivatives carrying thienyl-, 3,4-ethylenedioxy-thienyl- (EDOT-) and 3,4-ethylenedithiathienyl- (EDTT-) substituent groups have been synthesized and electrochemically polymerized. The polymers were investigated using UV/vis absorption spectroscopy and cyclic voltammetry. It was found that the growth of the polymers proceeded as random coupling of the thiophene groups in the 2-,3-,5-, and 6-positions of the DPP chromophore. In the cross-linked polymers, conjugated sequences were only built through coupling of thiophene groups in 3,6-positions, and separated by non-conjugated sequences through coupling with thiophene units in other positions of the DPP core.     

A crystalline low-bandgap polymer comprising dithienosilole and thieno[3,4-c]pyrrole-4,6-dione units for bulk heterojunction solar cells

We have used Stille coupling polymerization to synthesize a new low-bandgap conjugated polymer, PDTSTPD, that consists of an electron-rich dithieno[3,2-b:2′,3′-d]-silole (DTS) unit and an electron-deficient thieno[3,4-c]pyrrole-4,6-dione (TPD) moiety. The polymer exhibited an excellent thermal stability, crystalline characteristics, a broad spectral absorption, and a deep highest occupied molecular orbital (HOMO) energy level, resulting from combination of the rigid TPD and the coplanar DTS units in the polymer backbone. Moreover, the presence of the silicon atoms along the polymer chain ensured PDTSTPD having strong interchain stacking and good hole mobility. An optimal device incorporating the PDTSTPD:PC₇₁BM blend at a weight ratio of 1:1 provided a power conversion efficiency of 3.42%.     

Fine tuning of frontier orbital energy levels in dithieno[3,2-b:2′,3′-d]silole-based copolymers based on the substituent effect of phenyl pendants

A series of dithieno[3,2-b:2′,3′-d]silole-based π-conjugated copolymers containing thieno[3,4-c]pyrrole-4,6-dione or thieno[3,4-b]thiophene units bearing 4-substituted phenyl pendants were synthesized and their thermal stability, optical properties and frontier orbital energy levels were systematically investigated. The introduction of electron-withdrawing substituents on the phenyl rings lowered their frontier orbital energy levels without deteriorating their thermal and optical properties. By replacing an electron-donating methoxy group with an electron-withdrawing trifluoromethyl group, both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital energy levels of the polymers were deepened by more than 0.3 eV. A relatively linear relationship was observed between the HOMO energy levels and the Hammett substituent constants.     

Electropolymerization kinetic study of 3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine and its optical optimization for electrochromic window applications

Poly (3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine), PProDOT-Me₂, is one of the most promising conducting polymers in the alkylenedioxythiophene based family for electrochromic window applications. In the electropolymerization kinetic study of 3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine (ProDOT-Me₂), microgravimetry and chronoamperometry were used to determine the reaction orders with respect to the electrolyte and monomer, and the corresponding general kinetic equation of electropolymerization. This study presents that monomer concentration has a strong impact on electropolymerization mechanism. The relationship between film thickness and polymerization time was analyzed indicating that saturation of polymerization reduced the increase rate of film thickness with polymerization time. Also, the electropolymerization conditions were optimized to reach high contrast (Δ%T > 70%) with the minimum of transmittance (%T_min < 1) for electrochromic window applications.     

Reactions with β-ketodianilides. I. New synthesis of Pyrido[3,4-c]pyridine Derivatives

Acetonedicarboxylic acid dianiline reacted with malononitrile, ethyl cyanoacetate or benzoylacetonitrile to give (6-amino-5-cyano-1,2-dihydro-2-oxo-1-phenylpyrid-4-yl)-acetanilide ( 3 ), (3-cyano-2,6-dioxo-1-phenyl-1,2,5,6-tetrahydropyrid-4-yl)acetanilide ( 8 ) or (3-cyano-1,6-dihydro-1,2-diphenyl-6-oxopyrid-4-yl)acetanilide ( 9 ). Compounds 3 and 8 could be cyclised into 8-amino-1,6-diphenyl-1,2,4,5,6,7-hexahydro-7-iminopyrido[3,4-c]pyridine-2,5-dione ( 4 ) and 7-amino-1,2,3,5,6,8-hexahydro-1,6-diphenylpyrido[3,4-c]pyridine-2,5,8-trione ( 10 ) respectively by heating their solutions in dimethylformamide in the presence of triethylamine. Each of 3 and 4 coupled with arenediazonium chlorides to give the corresponding arylhydrazone derivatives ( 5a–d ) and ( 6a–c ), respectively. Condensation of 4 with p-nitrosodimethylaniline yielded 8-amino-4- (p-dimethylaminophenylimino)-1,6-diphenyl-1,2,4,5,6,7-hexahydro-7-iminopyrido[3,4-c]pyridine2,5-dione ( 7 ).     

Synthesis and photovoltaic properties of donor–acceptor polymers incorporating a structurally-novel pyrrole-based imide-functionalized electron acceptor moiety

A structurally-novel pyrrole-based imide-functionalized electron accepting monomer unit, 4,6-dibromo-2,5-dioctylpyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (DPPD), was prepared. The new DPPD unit was copolymerized with pyrrole-based electron rich monomers, such as thiophene-(N-alkyl)pyrrole-thiophene (TPT) and fused thiophene-(N-alkyl)pyrrole-thiophene (DTP) derivatives, to afford two new polymers, namely P(TPT-DPPD) and P(DTP-DPPD), respectively. The two polymers showed a strong absorption band at 300–600 nm and 300–650 nm, respectively, and their calculated optical band gaps were 2.09 eV and 1.89 eV, respectively. The electrochemical analysis reveals that the highest occupied molecular orbital (HOMO) energy levels of P(TPT-DPPD) and P(DTP-DPPD) were positioned at −5.55 eV and −5.24 eV, respectively, whereas their lowest unoccupied molecular orbital (LUMO) energy levels were positioned at −3.46 eV and −3.35 eV, respectively. The preliminary photovoltaic properties of the polymers, P(TPT-DPPD) and P(DTP-DPPD), were examined by fabricating polymer solar cells (PSCs) with each polymer as an electron donor and PC₇₁BM as an electron acceptor. The PSCs fabricated with the configuration of ITO/PEDOT:PSS/P(TPT-DPPD) or P(DTP-DPPD):PC₇₁BM/LiF/Al showed maximum power conversion efficiency (PCE) of 0.73% and 1.64%, respectively.     

COMPARATIVE METABOLISM OF PHENANTHRO[3,4-B]THIOPHENE,PHENANTHRO[4,3-B]THIOPHENE AND THEIR CARBON ANALOG BENZO[C]PHENANTHRENE BY RAT LIVER MICROSOMES

Phenanthro[3,4-b]thiophene (P[3,4-b]T) and phenanthro[4,3-b]thiophene (P[4,3-b]T) are thiasters of weakly mutagenic benzo[c]phenanthrene (B[c]P). These polycyclic sulfur heterocycles (thia-PAHs) represent a group of chemicals which have been identified in cigarette smoke. P[3,4-b]T is a potent mutagen in Salmonella typhimurium strain TA100 in the presence of rat liver S9, whereas its isosteric isomer P[4,3-b]T is a nonmutagenic compound. In order to understand the mechanism underlying the differences in the mutagenic activity of P[3,4-b]T and P[4,3-b]T, we have investigated the metabolism of P[3,4-b]T, P[4,3-b]T, and their carbon analogue B[c]P by rat liver microsomes. The liver microsomes from rats treated with Aroclor 1254 metabolized P[3,4-b]T, P[3,4-b]T, and B[c]P at a rate nearly 7- to 9-fold greater than of the control liver microsomes. High-performance liquid chromatography (HPLC) analysis of the metabolites formed showed that B[c]P was metabolized almost exclusively to its dihydrodiols which comprised predominantly K-region diol as noted in the previous studies. Our preliminary studies on the metabolism of P[3,4-b]T, P[4,3-b]T and B[c]P by liver microsomes from control and Aroclor 1254-treated rats have shown a significant reduction in the formation of 6,7-diol (K-region diol) and 8,9-diol (diol with a bay-region double bond) of the two thia-PAHs compared to the formation of analogous 5,6-diol (K-region diol) and 3,4-diol (diol with a bay-region double bond) from B[c]P. Both P[3,4-b]T and P[4,3b]T produced a major, relatively nonpolar metabolite(s) (80–96% of total metabolites). These studies indicate that the highly mutagenic P[3,4-b]T is not metabolized to dihydrodiol with a bay-region double bond to any greater extent than the weakly or nonmutagenic B[c]P or P[4,3-b]T, suggesting that the metabolite(s) other than P[3,4-b]T8,9-diol is likely to be involved in the mutagenicity of P[3,4-b]T.     

The synthesis of pyrazolo- and isoxazolo-[3,4-c]-pyrazole hemiazadicarbocyanine dyes

New substituted pyrazolo and/or isoxazolo-[3,4-c]-pyrazole hemiazadicarbocyanine dyes (IV_a-d, V_a-d, VI_a-d) were prepared via the synthesis of 4-arylidino-1-phenyl-3-benzoxazolium-2-yl-pyrazol-5-one (II_a-d) followed by their interaction with hydrazine hydrate, phenylhydrazine and hydroxylamine. Structures of the synthesised compounds were determined from analytical data and from spectra. The biological activity of IV, V and VI were tested against bacteria and fungi.     

Polycarbonyl heterocyclics. [V]. Synthesis of pyrrolo[3,4-c]pyridine and Furo[3,4-c]-pyridine derivatives by the Ring Transformation of Thiazolidine-4-on Derivatives

2-(Aroyl, methylidene)-3-aryl-5-dicyanomethylene thiazolidine-4-on derivatives 2 under morpholine treatment formed complex 3 . The acid hydrolysis of 3 leads to pyrrolo [3,4-c]-pyridine derivatives 4 . On treatment of 3 with aqueous sodium hydroxide and subsequent acidification [3,4-c]pyridine derivatives 5 are formed.     

Thieno[3,2-b]thiophene as π-bridge at different acceptor systems for electrochromic applications

Benzoselenadiazole, quinoxaline and thieno[3,2-b]thiophene are the units preferred in conducting polymers due to their electrochemical properties. There are no reports in the literature on polymers containing both moieties. In this study, novel benzoselenadiazole, quinoxaline and thieno[3,2-b]thiophene based monomers; 4-(3a,6a-dihydrothieno[3,2-b]thiophen-2-yl)-7-(thieno[3,2-b]thiophenyl)benzo[c][1,2,5]selenadiazole (BSeTT) and 2,3-bis(3,4-bis(decyloxy)phenyl)-5,8-dibromo-2,3-dihydroquinoxaline (QTT) were synthesized via Stille Coupling and polymerized electrochemically. These polymers were characterized in terms of their spectroelectrochemical and electrochemical properties by cyclic voltammetry and UV–Vis–NIR spectroscopy. Spectroelectrochemistry analysis of PBSeTT revealed an electronic transition at 525 nm corresponding to π–π* transition with a band gap of 0.93 eV whereas PQTT revealed electronic transitions at 440 and 600 nm corresponding to π–π* transitions with a band gap of 1.30 eV. Electrochromic investigations showed that PBSeTT has gray color PQTT switching between green and gray. Switching time of the polymers was evaluated by a kinetic study upon measuring the percent transmittance (%T) at the maximum contrast point.     

Medium Bandgap Polymers for Efficient Non-Fullerene Polymer Solar Cells—An In-Depth Study of Structural Diversity of Polymer Structure

A series of medium bandgap polymer donors, named poly(1-(5-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo [1,2-b:4,5-b′]dithiophen-2-yl)thiophen-2-yl)-5-((4,5-dihexylthiophen-2-yl)methylene)-3-(thiophen-2-yl)-4H-cyclopenta[c]thiophene-4,6(5H)-dione) (IND-T-BDTF), poly(1-(5-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo [1,2-b:4,5-b′]dithiophen-2-yl)-4-hexylthiophen-2-yl)-5-((4,5-dihexylthiophen-2-yl)methylene)-3-(4-hexylthiophen-2-yl)-4H-cyclopenta[c]thiophene-4,6(5H)-dione (IND-HT-BDTF), and poly(1-(5-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo [1,2-b:4,5-b′]dithiophen-2-yl)-6-octylthieno [3,2-b]thiophen-2-yl)-5-((4,5-dihexylthiophen-2-yl)methylene)-3-(6-octylthieno [3,2-b]thiophen-2-yl)-4H-cyclopenta[c]thiophene-4,6(5H)-dione (IND-OTT-BDTF), are developed for non-fullerene acceptors (NFAs) polymer solar cells (PSCs). Three polymers consist of donor-acceptor building block, where the electron-donating fluorinated benzodithiophene (BDTF) unit is linked to the electron-accepting 4H-cyclopenta[c]thiophene-4,6(5H)-dione (IND) derivative via thiophene (T) or thieno [3,2-b]thiopene (TT) bridges. The absorption range of the polymer donors based on IND in this study shows 400~800 nm, which complimenting the absorption of Y6BO (600~1000 nm). The PSC’s performances are also significantly impacted by the π-bridges. NFAs inverted type PSCs based on polymer donors and Y6BO acceptor are fabricated. The power conversion efficiency (PCE) of the device based on IND-OTT-BDTF reaches up to 11.69% among all polymers with a short circuit current of 26.37 mA/cm², an open circuit voltage of 0.79 V, and a fill factor of 56.2%, respectively. This study provides fundamental information on the invention of new polymer donors for NFA-based PSCs.     

Significant enhancement of thermoelectric properties of conducting PTB7 polymer by addition of appropriate dopants

Thermoelectric properties of poly({4,8-bis [(2-ethylhexyl)oxy] benzo [1,2-b:4,5-b'] dithiophene-2,6- diyl}{3-fluoro-2- [(2-ethylhexyl) carbonyl] thieno[3,4-b] thiophenediyl}), commonly known as PTB7 conducting polymer was investigated for the first time by the first author in 2017, and it showed higher electrical conductivity or Seebeck coefficient (or even both) and hence, higher thermoelectric power factor than a variety of organic semiconductors. Therefore, it is worth working more on this semiconductor to improve its thermoelectric power factor. In this work, for the first time, 4 new dopants are introduced to PTB7 polymer to improve its thermoelectric properties. The materials are famous oxidants that are inexpensive and easily available with no need to perform any synthesis process, including antimony pentachloride (SbCl₅), iron trichloride (FeCl₃), thionyl chloride (SOCl₂), and iodine (I₂). As a result, significant enhancement of thermoelectric power factor after doping with antimony pentachloride (from 0.224 to 25.5 μWK⁻² m⁻¹,) and iron trichloride (from 0.224 to 18.2 μWK⁻² m⁻¹,) and moderate enhancement with thionyl chloride was obtained. For the case of iodine doping, simultaneous enhancement of electrical conductivity and Seebeck coefficient was observed due to increasing the mobility.     

A new series of random conjugated copolymers containing 3,4-diphenyl-maleimide and thiophene units for organic photovoltaic cell applications

A series of random conjugated copolymers (labeled PMLTQT, PMLT2T, and PMLT3T) consisting of 3,4-diphenyl-maleimide and various thiophene derivatives has been designed and synthesized via Stille cross-coupling for application in polymer solar cells. These copolymers were readily soluble in common organic solvents, thermally stable from 405 to 437 °C upon heating, and exhibited good absorption in the UV and visible regions from 300 to 650 nm. The intensities of the PL emission spectra of these copolymers in a solid film were dramatically quenched by the addition of 50 wt% [6,6]-phenyl C₆₁ butyric acid methyl ester (PC₆₁BM). Their electrochemical properties indicated that the highest occupied molecular orbital levels of these copolymers were in the range of ?5.63–5.73 eV, characteristic of better air stability and a high open-circuit voltage (V_oc) suitable for application to photovoltaic cells. Bulk heterojunction photovoltaic devices composed of an active layer of electron-donor copolymers blended with the electron acceptor PC₆₁BM or [6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) at a weight ratio of 1:3 were investigated. The photovoltaic device containing PMLT3T and PC₇₁BM (1:3, w/w) as the active layer afforded the best performance among these copolymers, with a V_oc of 0.74 V, J_sc of 7.4 mA cm^?2 and a PCE of 1.20% under AM 1.5 G simulated solar light.     

A nitrogen rich Ni(II)–dithiolate system exhibiting acid–base behavior: Synthesis,supramolecular structure and spectroscopy of [Bu4N]2[NiII(ppdt)2] (ppdt = pyrido[2,3-b]pyrazine-2,3-dithiolate)

The compound [Bu₄N]₂[Ni(ppdt)₂] (1) (ppdt = pyrido[2,3-b]pyrazine-2,3-dithiolate) has been synthesized, starting from pyrido[2,3-b]pyrazine-2,3-dithiol, nickel chloride and tetrabutylammonium bromide in methanol. Compound 1 crystallizes in P2₁/c space group (monoclinic system). Its crystal structure is characterized by interesting C–H?S and C–H?N supramolecular weak interactions. Its solution state has been described with acid–base (protonation–deprotonation) behavior, that has rarely been investigated for a metal–dithiolene system. Compound 1 is first instance of a metal–dithiolene compound that has three ring nitrogen on each dithiolate ligand. The pH dependent changes in the charge-transfer absorption band are attributed to the protonation on an imine nitrogen of the ppdt ligand. The complex is electrochemically quasi-reversible with an oxidation potential of E_1/2 = +0.46 V vs. Ag/AgCl in methanol.     

Synthesis of novel narrow-band-gap copolymers based on [1,2,5]thiadiazolo[3,4-f]benzotriazole and their application in bulk-heterojunction photovoltaic devices

Two novel conjugated alternating copolymers with [1,2,5]thiadiazolo[3,4-f]benzotriazole as acceptor and 9,9-dioctylfluorene or N-9’-heptadecanyl-carbazole as donors respectively, were synthesized by Suzuki polycondensation. Both of the two copolymers have nearly ideal band gaps and show excellent absorption spectra in near infrared region. Polymer solar cells based on the blends of them and [6,6]-phenyl-C₇₁ butyric acid methyl ester show excellent performance when using a water/alcohol soluble conjugated polymer as cathode interlayer, which exhibit a maximum power conversion efficiency of 3.17% with the short-circuit current density of 8.50 mA/cm², the open-circuit voltage of 0.70 V and the fill factor of 41%. Our results demonstrate that [1,2,5]thiadiazolo[3,4-f]benzotriazole is a promising acceptor unit for low band gap polymer donor materials design.     

Synthesis and characterization of light‐absorbing cyclopentadithiophene‐based donor–acceptor copolymers

Cyclopentadithiophene and benzothiadiazole based donor–acceptor polymers are fast emerging as the most promising class of materials for organic solar cells. Here we report on a series of Cyclopentadithiophene and benzothiadiazole based conjugated polymers, namely poly[4,7‐bis(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole] (P1), poly[4,7‐bis(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole‐alt‐9‐(heptadecan‐9‐yl)‐2,7‐bis(4,4,5,5‐tetramethyl)‐1,3,2‐dioxaborolan‐2‐yl)‐9H‐carbazole] (P2) and poly[4,7‐bis(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole‐alt‐5,11‐bis(2‐hexyldecyl)‐3,9‐bis(4,4,5,5‐tetramethyl)‐1,3,2‐dioxaborolan‐2‐yl)‐5,11‐dihydroindolo[3,2‐b]carbazole] (P3), with alternating donor and acceptor units and discuss their photophysical and electrochemical properties. Stille coupling of 2‐tributylstannyl‐4,4‐dioctylcyclopenta[2,1‐b:3,4‐b′]dithiophene with 4,7‐dibromobenzo[1,2,5]thiadiazole generated the alternating donor–acceptor monomer 4,7‐bis(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole (CPDT‐BT‐CPDT). Homopolymer P1 of CPDT‐BT‐CPDT was synthesized by oxidative polymerization using FeCl₃. Copolymers P2 and P3 were synthesized by palladium‐catalysed Suzuki polycondensation. The synthesized polymers showed good solubility in common organic solvents, and UV‐visible measurements showed that the absorption maxima of the polymers lie in the range 624 to 670 nm. The energy gaps of these polymers were found to lie in the range 1.29 to 1.50 eV. Gel permeation chromatography measurements against polystyrene standards showed the number‐average molecular weight to be in the range (2.2–6.0) × 10⁴ g mol^?1. Thermogravimetric analysis showed the polymers to possess high thermal stability. A preliminary study of photodiode devices prepared using polymers P1, P2 and P3 when blended with the PC₇₁BM electron acceptor found that P2 is the optimum chemical structure for pursuing further device optimization.© 2015 Society of Chemical Industry     

Effects of high-boiling-point additive 2-Bromonaphthalene on polymer solar cells fabricated in ambient air

High boiling point solvent additive, employed during the solution processing of active layer fabrications, impact the efficiency of bulk heterojunction polymer solar cells (PSC) by influencing the morphological of the active layer. The photovoltaic performances of the PSCs based on the donor of poly{4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]-dithiophene-2,6-diyl-alt-3-fluoro-2-[(2 ethylhexyl)carbonyl] thieno[3,4-b]thiophene-4,6-diy (PTB7) and the acceptor of [6, 6]-phenyl-C71-butyric-acidmethyl-ester (PC₇₁BM) was optimized using 5 vol% high-boiling-point solvent additive of 2-Bromonaphthalene (BN). The optimized air-processed PSC based on PTB7:PC₇₁BM (1:1.5 w/w) with 5 vol% BN exhibited a power conversion efficiency of 7.01% with open-circuit voltage (V _oc) of 0.731 V, short-circuit current density (J _sc) of 13.79 mA cm^?2, and fill factor (FF) of 69.46%. The effects of the additive on photovoltaic performances were illustrated with atomic force microscopy and transmission electron microscope measurements. Our results indicate that the improved efficiency is due to the optimized PTB7/PC₇₁BM interpenetrating network and the enhanced absorption of the active layer using the BN as solvent additive.     

Preparation and characterization of polyisoprenes and polybutadienes having 1,2- and 3,4-linkages preferentially

Polyisoprenes (PI) and polybutadienes (PB) both having vinyl-type side chains preferentially were prepared and characterized. Both polymers were anionically polymerized with cumyl potassium or pottassium naphthalenide as initiators in a polar solvent, tetrahydrofuran, at low temperature. From the ¹H NMR measurement, the PI contains 3,4- and 1,2-microstructures and PB does 1,2-microstructure preferentially. All the samples covering the molecular weight range of 37 k ≤ M_w ≤ 724 k for PI and 35 k ≤ M_w ≤ 197 k for PB were confirmed to have narrow molecular weight distribution. Measured glass transition temperatures, i.e., 11.0 °C for PI and ?0.7 °C for PB are both considerably high compared with those of 1,4-microstructure-rich analogues. Intrinsic viscosity measurements in 1,3-dioxane for PI and 2-octanol for PB were carried out, and the segment lengths of the 3,4-/1,2-rich PI and 1,2-rich PB were estimated to be 0.60 nm and 0.59 nm, which are both considerably shorter than the values for two polydienes having 1,4-microstructures preferentially, i.e., 0.66 nm for both 1,4-rich PI and PB. Furthermore plateau moduli of both polymers are determined by dynamic viscoelastic measurements.