Trifluoromethyl benzimidazole-based conjugated polymers with deep HOMO levels for organic photovoltaics

We synthesized new alternating conjugated polymers, PCDTFMMBI and PBDTDTFMMBI, which consist of trifluoromethyl substituted dimethyl-2H-benzimidazole (FMMBI) as new electron deficient unit, by palladium(0)-catalyzed Suzuki or Stille polymerization. Trifluoromethyl group has attractive features such as high solubility, chemical and thermal stability and strong electron withdrawing ability to adjust redox potentials. In addition to this, the introduction of trifluoromethyl group into benzimidazole unit will expand the absorption range into the longer wavelength region. Poly(4,8-bis(2-octyldodecyloxy) benzo[1,2-b:3,4-b]dithiophene-alt-5,5-(2-methyl-4???,7???-di-(2-thienyl)-2-(trifluoromethyl)-2H-benzimidazole)) (PBDTDTFMMBI) film, in which benzodithiophene unit was introduced as the electron rich unit, showed an absorption onset at 932 nm, corresponding to a low band gap of 1.33 eV. Poly(N-9???-heptadecanyl-2,7-carbazole-alt-5,5-(2-methyl-4???,7???-di-(2-thienyl)-2-(trifluoromethyl)-2H-benzimidazole)) (PCDTFMMBI), with carbazole as the electron rich unit, showed low lying HOMO energy level of -5.69 eV.close0

Design of a four-element array for accurate direction of arrival estimation in phase interferometry systems

This article proposes the design of a four-element array antenna for the accurate direction of arrival (DOA) estimation of Global Positioning System (GPS) interference signals. The proposed array antenna has four individual antenna elements, and each element consists of a radiating patch on the upper layer and a feeding loop on the lower layer. The patch and loop are intentionally designed in a circular shape to obtain the symmetric current distributions on the radiators. The feeding loop is directly connected by two output ports of an external hybrid chip coupler, and the radiating patch is then electromagnetically coupled by near-fields of the feeding loop. This feeding mechanism in the proposed structure allows for a more uniform current and H-field distribution for phase characteristics of the radiation that are close to the ideal isotropic radiators in the azimuth angle. In addition, the high-dielectric ceramic substrate is adopted to minimize the physical height of the antenna for the phase characteristics of the radiation close to the ideal isotropic radiators in elevation angles. To validate that the phase characteristics are similar to those of an ideal radiator, the DOA estimation performances are observed using a dual-axis interferometry. The results demonstrate that the proposed four-element array antenna with phase difference characteristics similar to those of an ideal radiator is suitable for the accurate DOA estimation of GPS interference signals

Novel 4,7-Dithien-2-yl-2,1,3-benzothiadiazole-based Conjugated Copolymers with Cyano Group in Vinylene Unit for Photovoltaic Applications

Two novel conjugated copolymers utilizing 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DTBT) coupled with cyano (-CN) substituted vinylene, as the electron deficient moeity, have been synthesized and evaluated in bulk heterojunction solar cell. The electron deficient moeity was coupled with carbazole and fluorene unit by Knoevenagel condition to provide poly(bis-2,7-((Z)-1-cyano-2-(5-(7-(2-thienyl)-2,1,3-benzothiadiazol-4-yl)-2-thienyl-ethenyl)-alt-9-(1-octylnonyl)-9H-carbazol-2-yl-2-butenenitrile) (PCVCNDTBT) and poly(bis-2,7((Z)-1-cyano-2-(5-(7-(2-thienyl)-2,1,3-benzothiadiazol-4-yl)-2-thienyl)ethenyl)-alt-9,9-dihexyl-9H-fluoren-2-yl) (PFVCNDTBT). The optical band gaps of PCVCNDTBT (1.74 eV) and PFVCNDTBT (1.80 eV) are lower than those of PCDTBT (1.88 eV) and PFVDTBT (2.13 eV), which is advantageous to provide better coverage of the solar spectrum in the longer wavelength region. The high V-oc value of the PSC of PCVCNDTBT (similar to 0.91 V) is attributed to its lower HOMO energy level (-5.6 eV) as compared to PCDTBT (-5.5 eV). Bulk heterojunction solar cells based on the blends of the polymers with [6,6]phenyl-C-61-butyric acid methyl ester (PC61BM) gave power conversion efficiencies of 0.76% for PCVCNDTBT under AM 1.5, 100 mW/cm(2).close

Synthesis and properties of low band gap polymers based on thienyl thienoindole as a new electron-rich unit for organic photovoltaics

A series of polymers based on 6-(2-thienyl)-4H-thieno[3,2-b]indole (TTI), a new electron-rich unit for organic photovoltaics, was synthesized. By replacing the six-membered benzene ring of the carbazole with an electron-rich five-membered thiophene ring, an enhanced ICT effect between the electron-rich group and the electron-deficient group is expected to result in improved p-electron delocalization, low band gap and increased light-harvesting ability of the OPVs. The TTI unit, with a fused rigid backbone, has an efficient structure for the ICT effect and for tuning of the HOMO and LUMO energy levels to generate a low band gap. As electron-deficient units, 4,7-bis(4-hexylthiophen-2-yl)-2,1,3-benzothiadiazole (DTBT-h), 2-dimethyl-4,7-di(2-thienyl)-2H-benzimidazole (DTMBI) and 3,6-di(2-thienyl)-2,5 dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP) were introduced by using Stille polymerization. PTTIDTMBI and PTTIDPP have low band gaps and show absorption up to 849 and 948 nm, respectively. The highest PCE was achieved with the device fabricated from a PTTIDTBT-h : PC71BM (1 : 3 w/w) blend with 1,8-octanedithiol (ODT) as an additive. The device demonstrated a V-oc value of 0.81 V, a J(sc) value of 8.19 mA cm(-2), and an FF of 0.51, giving a highest power conversion efficiency of 3.35%.close0

Syntheses and solar cell applications of conjugated copolymers consisting of 3,3 '-dicarboximide and benzodithiophene units with thiophene and bithiophene linkage

Novel conjugated copolymers consisting of bis(2-octyldodecyloxy)benzo[1,2-b:3,4-b]dithiophene (BDT) and N-alkyl-2,2'-bithiophene-3,3'-dicarboximide (BTI) with thiophene and bithiophene linkages have been synthesized and evaluated in bulk heterojunction solar cell. BDT, BTI and thiophene (or bithiophene) units were incorporated using Stille polymerization to generate poly(5-dodecyl-3-(2-thienyl)-4H-dithieno[3,2-c:2,3-e]azepine-4,6(5H)-dione-co-4,8-di(2-octyldodecyloxy)benzo[1,2-b;3,4-b]dithiophene) (P1, P2 and P3) and poly(5-dodecyl-3-di(thien-2-yl)-4H-dithieno[3,2-c:2,3-e]azepine-4,6(5H)-dione-co-4,8-di(2-octyldodecyloxy)benzo[1,2-b:3,4-b]dithiophene) (P4, P5 and P6). The BTI unit, as the electron deficient moeity, and the BDT-thiophene (or bithiophene) unit, as the electron rich moeity, have been applied for the efficient intramolecular charge transfer. The introduction of thiophene or bithiophene unit improved power conversion efficiency (PCE) of the OPVs. The best device with P2:PC61BM (1:1) showed a open circuit voltage (V-OC) of 0.88 V, a short circuit current (J(SC)) of 7.36 mA/cm(2), and fill factor (FF) of 0.63, which yield PCE of 4.17%. (C) 2015 Elsevier B.V. All rights reservedclose0

Synthesis and characterization of fluorene-carbazole and fluorene-phenothiazine copolymers with carbazole and oxadiazole pendants for organic light emitting diodes

We report the synthesis and characterization of new series of the fluorene based polymers with carbazole and oxadiazole pendants for the generation of the white emission out of the EL device. In the fluorene backbone, hole transporting units such as carbazole or phenothiazine were incorporated to improve the EL brightness and efficiency. The PFCzOxd-co-PCzs and PFCzOxd-co-PPTZs in EL spectra showed maximum peaks at around 430 nm and additional large peaks at around 530 and 500 nm, respectively. In case of PFCzOxd-alt-PCz and PFCzCzPCz-co-PFOxdOxdPCz. the EL spectra of the polymers showed two distinct peaks comprising the maximum at 427 nm, which corresponds to the EL spectra of the conjugated backbone, and additional broad peaks at around 540 and 530 nm, respectively. The CIE coordinates of the devices from PFCzOxd-alt-PCz and PFCzCzPCz-co-PFOxdOxdPCz were (0.28, 0.33) and (0.25, 0.32), respectively, approaching the value of the standard white of National Television System Committee (NTSC) (0.33, 0.33).close91

Conjugated polymers containing 6-(2-thienyl)-4H-thieno[3,2-b]indole (TTI) and isoindigo for organic photovoltaics

Conjugated polymers using 6-(2-thienyl)-4H-thieno[3,2-b]indole (TTI) and isoindigo (ID) were synthesized and applied to the polymer solar cells. TTI as electron pushing unit and ID as electron pulling unit were incorporated in the push-pull types of conjugated polymers (PTTIID, PTTIID-3, PTTIID-5 and PTTIID-7). The alternating copolymer with TTI and ID units was synthesized in addition to the corresponding random copolymers. The UV-vis absorption spectra of the random copolymers showed red-shifted maximum peaks and wider full width at the half maximum (fwhm) with raising percentages of ID contents. Synthesized polymers shows deeper highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels with increased percentage of ID as electron pulling unit. As compared to the alternating copolymer PTTIID, the random copolymer PTTIID-7 showed higher JSC and FF values caused by the better morphology and decent hole mobility, resulting in higher PCE value. The device comprising PTTIID-7 and PCBM (1:2) with chloronaphthalene (CN) additive showed a VOC of 0.63 V, a JSC of 12.3 mA/cm2, and a fill factor (FF) of 0.52, giving a power conversion efficiency (PCE) of 4.03%.clos

Syntheses and solar cell applications of conjugated copolymers containing tetrafluorophenylene units

Novel conjugated copolymers containing tetrafluorophenylene unit have been synthesized and evaluated in bulk heterojunction solar cell. The tetrafluorophenylene unit, as the strong electron deficient moeity, has been applied for the syntheses of donor-acceptor type copolymers with a narrow-band-gap for bulk heterojunction solar cells. DTBT, tetrafluorophenylene and four types of BDT derivatives as the electron rich units were incorporated using Stille polymerization to generate PE-BDTF, PO-BDTF, PE-BDTTF and PO-BDTTF. The introduction of even 1% of tetrafluorophenylene unit substituting DTBT of BDTDTBT type of polymers results in significant decrease of the band gap of the polymers. The device with PO-BDTF: PC71BM (1:1) showed an open-circuit voltage (V-OC) of 0.75 V, a short circuit current (J(SC)) of 11.80 mA/cm(2), and a fill factor (FF) of 0.59, which yields PCE of 5.22%. (C) 2015 Elsevier Ltd. All rights reservedclose

Synthesis and photovoltaic properties of alkoxy-benzimidazole containing low band gap polymers

Dioctyloxy substituted dimethyl-2H-benzimidazole (4,7-dibromo-5,6-dioctyloxy-2,2-dimethyl-2H-indene, DOMBI) was prepared and copolymerized with thiophene (or bithiophene) and carbazole using both Stille and Suzuki polymerization. In DOMBI, the sulfur at 2-position of 2,1,3-benzothiadiazole (BT) unit was replaced with dialkyl substituted carbon and dioctyloxy groups were introduced at 5,6-position of dimethyl-2H-benzimidazole (MBI) unit. DOMBI unit is still keeping 1,2-quinoid form with two alkyl groups on the carbon which substitute the sulfur of BT. In addition to this, dioctyloxy groups on 5,6-position will improve the absorption at the longer wavelength region. The poly(2,2-dimethyl-5,6-bis(octyloxy)-4-(2-thienyl)-2H-bezimidazole) (PTDOMBI) thin films show absorption band with peaks at 357 and 656 nm and an absorption onset at 775 nm, corresponding to a band gap of 1.60 eV. The devices with PTDOMBI with [6,6]phenyl-C71-butyric acid methyl ester showed power conversion efficiency of 0.76%.close0