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Herein, two copolymers, poly [(6,6,12,12-tetraoctylindenofluorene)- co -(2,1,3-benzothiadiazole)] (PIFL-BT) and poly [(6,6,12,12-tetraoctylindenofluorene)- co -(2,1,3- benzooxadiazole)] (PIFL-BO) were synthesized and characterized. The effect of two electron accepting moieties benzothiadiazole (BT) and benzooxadiazole (BO) in combination with common tetraalkyl substituted indenofluorene building block in the backbone of conjugated polymer is studied in detail via thermal, optical, and electrochemical characteristics. To investigate the electroluminescence characteristics, both organic light emitting diodes (OLEDs) and light emitting electrochemical cells (LECs) devices are fabricated using copolymers as an active light-emitting layer. For the OLED devices, only polymer PIFL-BT emitted yellow light with CIE coordinates of (0.43, 0.55), a maximum current efficiency (CE max) of 0.24 cd/A, a maximum power efficiency (PE max) of 0.11 lm/W and a maximum brightness (MB max) of 1398 cd/m2. For the LEC device, both materials showed light emission and higher current density than OLEDs devices, indicating better carrier injection in LECs. Image 1 • Two light emitting indenofluorene copolymers with benzothiadiazole (PIFL-BT) and benzooxadiazole (PIFL-BO) were synthesized and characterized. • The effect of two electron accepting moieties such as benzothiodiazole (BT) and benzooxadiazole (BO) are studied in detail. • Both polymers were evaluated as an active light-emitting layer in organic light emitting diodes (OLEDs) and light emitting electrochemical cells (LECs) devices. • PIFL-BT emitted yellow emission in OLED devices whereas both polymers showed light emission in LECs. [ABSTRACT FROM AUTHOR]

This paper demonstrates the designing of π-conjugated donor small organic molecule 4,7-bis(5-((E)-3,5-dimethoxystyryl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (BTD-2OMe) and its synthesis through the multistep synthetic routes from commercially available low cost precursor materials. The π-conjugated thiophene units interconnected with vinylene in BTD-2OMe favor the red shift absorption spectrum. Thermogravimetric (TGA) and differential scanning calorimetry (DSC) analysis of BTD-2OMe present excellent thermal stability up to ∼403 °C with only 3% weight loss and good crystallization of organic chromophore, respectively. The absorption band in solid state shows the red shift due to J-aggregation and a moderate optical bandgap of ∼1.81 eV with HOMO-LUMO energy levels of −5.35 and −3.54 eV has been obtained. The bulk heterojunction organic solar devices (BHJ-OSCs) have been fabricated and are systematically investigated with different BTD-2OMe:PC 71 BM (1:1, 1:2, and 1:3, w/w) active layers. The optimized BTD-2OMe:PC 71 BM (1:2, w/w) device with improved active layer morphology and balanced energy level alignment achieves a high short circuit current density (Jsc) of ∼13.13 mAcm−2 and open-circuit voltage (Voc) of ∼0.924 V resulting in power conversion efficiency (PCE) of ∼6.72%. Importantly, the optimized BTD-2OMePC 71 BM (1:2, w/w) device poses significantly high device stability of up to 15 days under ambient temperature by retaining ∼95% of PCE from its initial value. [Display omitted] • A novel π-conjugated donor small organic molecule BTD-2OMe is synthesized. • BTD-2OMe with π-conjugated thiophene units interconnected with vinylene group improved optical properties. • Fabricated BHJ-OSCs with BTD-2MeO:PC 71 BM active layer depicts a high PCE of ∼6.72%. • Fabricated BHJ-OSC exhibits a high device stability upto 15 days under ambient temperature. [ABSTRACT FROM AUTHOR]

We report the evaluation of charge transport parameters of four p-type dichlorinated-2,1,3-benzothiadiazole (2ClBT) based conjugated polymers end-capped with different electron-donor units (thiophene (T), thieno[3,2- b ]thiophene (TT), 2,2′-bithiophene (DT), and (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TVT)) in electrolyte gated organic field-effect transistors operating at a driving voltage of −2 V. Remarkable hole mobility improvement of 0.13–0.56 cm 2 V −1 s −1 were achieved in 2ClBTs based polymers, with P2ClBT-DT recording the highest mobility of 0.56 cm 2 V −1 s −1 and current on/off ratio ∼10 7 . Interestingly, a positive threshold voltage shift (Δ V Th ) was observed in the transfer characteristics from the linear to saturation regime of all the 2ClBTs based polymer electrolyte gated OFET devices of L = 10 μm, contrary to devices with conventional poly(methyl methacrylate) gate dielectric, which showed a negative Δ V Th shift. Among the 2ClBTs based polymers, P2ClBT-TVT devices showed the lowest mobility and Δ V Th shift, which is attributed to severe ion diffusion in the polymer semiconducting layer owing to the vinyl group backbone susceptible to electrochemical doping. Our results emphasize essential selection consideration of the monomeric moieties, molecular ordering, π-π stacking and backbone planarity of conjugated polymers for electrolyte based organic devices. [ABSTRACT FROM AUTHOR]

A series of fluorinated quinoxaline-based polymers with typical donor-π-acceptor configurations has been synthesized by Stille coupling reaction. The electron-donating dialkoxy-substituted benzodithiophene ( BDT ) is connected to the electron-withdrawing 2,3-diphenylquinoxaline ( DPQ ) acceptor through a thiophene bridge. To investigate the effect of strong electron-withdrawing moieties, fluorine atoms have been systematically incorporated at various positions on the DPQ units such as the 6,7-positions, the para -positions of the phenyl substituent on the 2,3-positions, and both locations to afford PBDT-QxF , PBDT-FQx , and PBDT-FQxF , respectively. Because of significant contributions from the fluorine atoms, these polymers display quite differentiated optical and electrochemical properties in comparison with those of their non-fluorinated counterpart, PBDT-Qx . In addition, a gradual improvement in power conversion efficiencies (PCEs) is observed in the order of PBDT-Qx , PBDT-QxF , PBDT-FQx , and PBDT-FQxF , when inverted-type polymer solar cells (PSCs) with a configuration of ITO/ZnO/polymers:PC 71 BM/MoO 3 /Al were fabricated. In particular, PBDT-FQxF , with four fluorine atoms on the 6,7-positions and the para -positions of the phenyl substituent on 2,3-positions of DPQ, exhibits the highest PCE of 6.60% with an open-circuit voltage ( V oc ) of 0.91 V, a short-circuit current density ( J sc ) of 10.15 mA/cm −2 , and a fill factor ( FF ) of 71.5%. [ABSTRACT FROM AUTHOR]

The effect of incorporating chalcogenophene comonomers, namely, furan, thiophene, and selenophene, on the optoelectrical properties of cyclopentadithiophene-based polymers (P1, P2, and P3, respectively) for organic field-effect transistors is reported. The optical, electrical, and morphological properties of the P1, P2, and P3 are investigated. Compared to the other polymers, the P2 showed the highest crystallinity with the shortest π–π stacking distance (d π–π ≈ 3.58 Å) and the longest crystalline length (L c ≈ 40 Å), as confirmed by two-dimensional grazing incidence wide-angle X-ray diffraction. However, P3 had the highest hole mobility (μ = 0.25 cm2/V-s), which is higher than P1 (μ = 0.06 cm2/V-s) and P2 (μ = 0.20 cm2/V-s). The relatively lower mobility of the P2 compared to that of the P3 is attributed to its island-like crystalline domains, confirmed by atomic force microscopy results and the lower edge-on crystallite ratio. Our findings suggest a new design guideline for developing high-mobility π-conjugated polymers. [Display omitted] • We first address the importance of size of substituted atoms in determining optoelectronic properties and thin film crystallinity of the FBT-based polymers. • The influence of chalcogenophene atom substitution on optoelectrical properties of the FBT-based polymers was thorough investigated. • Combining a highly-crystallized molecular packing with effective morphologies led to the best hole mobilities of 0.25 cm2V−1s−1 for P3. [ABSTRACT FROM AUTHOR]

We report high-performance organic thin-film transistors (OTFTs) with an ultrathin active layer of difluorobenzothiadiazole-dithienosilole copolymer (PDFDT) form by using the wire bar-coating process. The top-gate/bottom contact (TG/BC) OTFTs based on bar-coated PDFDT polymer as channel material and poly(methyl methacrylate) (PMMA) as gate dielectric show a hole mobility of up to 2.2 cm 2 V −1 s −1 with a current ON/OFF ratio ( I on / I off ) of 10 4 ∼10 5 , with the mobility being two times larger than that of the spin-coated PDFDT based OTFTs. The higher mobility of the bar-coated PDFDT polymer films can be attributed to the well-organized fibril structures of the polymer chains. Importantly, two different molecular weight polymers ( M n = 23 and 34 kDa) were employed to conduct these experiments and both batches showed about the same performance, which mitigates the typical batch-to-batch variation in OTFT performance. Furthermore, we explored the operational stability of the bar-coated OTFTs in ambient air and nitrogen environments. The bias-stress and cycling tests between the ON/OFF states of the bar-coated devices showed high stability in both nitrogen and air. Conclusively, here we demonstrate that (i) a simple bar-coating process is a better method to control and obtain good polymer morphology in comparison to spin-coating, and (ii) the PDFDT polymer has great potential to provide good reproducibility and stability in large-area OTFT devices. [ABSTRACT FROM AUTHOR]

Highlights: [•] Four novel carbazole sensitizing dyes were synthesized. [•] The photovoltaic performance of carbazole dyes was investigated. [•] The optimal η of these carbazole dyes reaches 5.40%. [Copyright &y& Elsevier]

Highlights: [•] Novel conjugated copolymers containing benzothiadiazole entity is synthesized. [•] Tunable optical properties from the acceptor moiety of the copolymer. [•] OPV with power conversion efficiency of 1.78% is delivered. [ABSTRACT FROM AUTHOR]

Abstract: A new series of donor–acceptor–donor (D–A–D) type compounds consisting of dialkyl substituted 3,4-propylenedioxythiophene and benzothiadiazole units were synthesized and polymerized chemically and electrochemically to investigate the effect of alkyl chain length on the doping process of the conjugated polymers. It was found that the alkyl chain length plays a key role on both doping processes and the solubility of the polymer. It is also noteworthy that this new series of D–A–D electrochromes transmits or reflects the cyan color of the Cyan–Magenta–Yellow (CMY) color space in the neutral state which can be switched to transmissive grey when oxidized. [Copyright &y& Elsevier]

Abstract: Single layer white organic light emitting diodes (WOLED) are obtained with a polymeric blend, whose constituents are three polyfluorene (PF) based materials emitting in the three fundamental colours thanks to the insertion of a single monomeric unit with different chemical nature at the core of the PF chain. The peculiar choice of three fully compatible polymers allows us to obtain stable and homogeneous active layers for highly performing WOLEDs. The high quality white electroluminescence with chromaticity coordinates (0.32; 0.33), correlated colour temperature of 5893K and colour rendering index of 90, makes these compounds good candidates for low-cost solid-state lighting technologies. [ABSTRACT FROM AUTHOR]

Abstract: A new low-band gap small molecule (Se-SM), which contains dithyenyl-benzoselenadiazole as central unit and terminal cyanovinylene 4-nitrophenyls, was synthesized. In addition, a new phenylenevinylene copolymer (P) containing dithyenyl-dinitrobenzothiadiazole moieties was synthesized by Heck coupling. Se-SM showed broad absorption band with long-wavelength absorption maximum (λ a,max) at ∼640nm and optical band gap () of 1.67eV. Copolymer P had λ a,max around 420nm and of 2.31eV. The dark current–voltage characteristics and incident photon to current efficiency spectra of the devices based on copolymer P and Se-SM indicates that both materials behave as p-type organic semiconductors. The power conversion efficiency (PCE) of the photovoltaic devices based on these materials is low. However, the PCE of the devices fabricated with the blends of copolymer P or Se-SM with PCBM, was improved significantly. The increase is attributed to the formation of bulk heterojunction with increased interfacial area. The effect of the incorporation of Se-SM molecule on the photovoltaic properties of copolymer P:PCBM blend has been also investigated. The overall PCE of the copolymer P:PCBM:Se-SM device is approximately 2.24%, which is further enhanced up to 3.16%, when the thermally annealed blend is used. Therefore, we conclude that the Se-SM molecule increases the light harvesting property of the blend and also provides efficient path for holes and electron in copolymer and PCBM phases, respectively. [Copyright &y& Elsevier]

Abstract: Two new soluble vinylene compounds, TPA-TNP and BTD-TNP, which contained triphenylamine and benzothiadiazole segments, respectively, and terminal p-nitrophenyl units were synthesized and characterized. They showed high thermal stability with decomposition temperature above 450°C. Their absorption was broad and extended up to about 800nm with optical band gaps of 1.65–1.67eV. The long wavelength absorption maximum was located around in between 638 and 650nm. The presence of the electron-withdrawing nitro groups on the terminal phenyls broadened the absorption of these compounds. The current–voltage characteristics in dark and the IPCE spectra of the devices based on these compounds revealed that these materials behave as p-type organic semiconductors with hole mobility of the order of 10−5 cm2/Vs. The photovoltaic properties of these compounds blended with PCBM were investigated and the power conversion efficiency is 1.13% and 1.32% for TPA-TNP and BTD-TNP, respectively. The device with thermally annealed BTD-TNP photoactive film shows power conversion efficiency of about 2.42%. [Copyright &y& Elsevier]