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Two semiconducting conjugated polymers were synthesized via Stille polymerization. The structures combined unsubstituted or (triisopropylsilyl)ethynyl (TIPS)-substituted 2,6-bis(trimethylstannyl)benzo[1,2-b:4.5-b']dithiophene (BDT) as a donor unit and benzotriazole with a symmetrically branched alkyl side chain (DTBTz) as an acceptor unit. We investigated the effects of the different BDT moieties on the optical, electrochemical, and photovoltaic properties of the polymers and the film crystallinities and carrier mobilities. The optical-band-gap energies were measured to be 1.97 and 1.95 eV for PBDT-DTBTz and PTIPSBDT-DTBTz, respectively. Bulk heterojunction photovoltaic devices were fabricated and power conversion efficiencies of 5.5% and 2.9% were found for the PTIPSBDT-DTBTz- and PBDT-DTBTz-based devices, respectively. This difference was explained by the more optimal morphology and higher carrier mobility in the PTIPSBDT-DTBTz-based devices. This work demonstrates that, under the appropriate processing conditions, TIPS groups can change the molecular ordering and lower the highest occupied molecular orbital level, providing the potential for improved solar cell performance.

For the practical application of dye-sensitized solar cells (DSSCs), it is important to replace the conventional organic solvents based electrolyte with environmentally friendly and stable ones, due to the toxicity and leakage problems. Here we report a noble water-based thixotropic polymer gel electrolyte containing xanthan gum, which satisfies both the environmentally friendliness and stability against leakage and water intrusion. For application in DSSCs, it was possible to infiltrate the prepared electrolyte into the mesoporous TiO2 electrode at the fluidic state, resulting in sufficient penetration. As a result, this electrolyte exhibited similar conversion efficiency (4.78% at 100 mW cm(-2)) and an enhanced long-term stability compared to a water-based liquid electrolyte. The effects of water on the photovoltaic properties were examined elaborately from the cyclic voltammetry curves and impedance spectra. Despite the positive shift in the conduction band potential of the TiO2 electrode, the open-circuit voltage was enhanced by addition of water in the electrolyte due to the greater positive shift in the I(-)/I3(-) redox potential. However, due to the dye desorption and decreased diffusion coefficient caused by the water content, the short-circuit photocurrent density was reduced. These results will provide great insight into the development of efficient and stable water-based electrolytes.

A low‐bandgap PBDTDTPD polymer is synthesized. It is a donor‐acceptor‐type polymer that consists of dialkylthiophenyl benzodithiophene (BDT) donor unit and N‐octyl‐2,7‐dithia‐5‐aza‐cyclopenta[a]pentalene‐4,6‐dione (DTPD) acceptor unit. The thienothiophene‐fused strong‐electron‐withdrawing DTPD effectively reduces the bandgap of the resulting polymer and keeps its highest occupied molecular orbital low. Moreover, PBDTDTPD is thermally stable and dissolves well in typical organic solvents. PBDTDTPD:PC71BM(1:1) blend film showed a power conversion efficiency of 3.18% and a largely elevated open‐circuit voltage of 0.75 V compared to that of well‐known P3HT:PC61BM blend film. In this work, we prove that the DTPD moiety can be utilized to develop a future low‐bandgap material that can absorb a broad wavelength of light and have high thermal stability, which are important characteristics for next‐generation high‐performance organic solar cells. [ABSTRACT FROM AUTHOR]

The effect of molecular weight of a series of conjugated polymers (CPs) on the doping efficiency, electrical conductivity, and related thermoelectric properties of doped CPs is studied. Low (L), medium (M), and high (H) molecular weight batches of PDFD‐T polymers, based on difluorobenzothiadiazole and dithienosilole moieties, are synthesized and denoted as PDFD‐T(L), PDFD‐T(M), and PDFD‐T(H), respectively. Furthermore, to compare the effects of different donor moieties, donor units of PDFD‐T(L) are structurally modified from thiophene to thienothiophene (TT) and dithienothiophene (DTT), denoted as PDFD‐TT(L) and PDFD‐DTT(L), respectively. After doping the CPs with FeCl3, d‐PDFD‐T(H) exhibits an electrical conductivity of 402.9 S cm−1, which is significantly higher than those of d‐PDFD‐T(L), d‐PDFD‐T(M), d‐PDFD‐TT(L), and d‐PDFD‐DTT(L). The highest power factor of 101.1 µW m−1 K−2 is achieved through organic thermoelectric devices fabricated using PDFD‐T(H). Through various characterizations, it is demonstrated that CPs with a high molecular weight tend to have a high carrier mobility while maintaining their original crystallinity and good charge transport pathways even after doping. Therefore, it is suggested that optimizing the molecular weight of CPs is an essential strategy for maximal power generation from their doped CP films. [ABSTRACT FROM AUTHOR]

Donor–acceptor (D–A) copolymer‐based polymer solar cells (PSCs) processed with nonhalogenated solvents exhibit relatively low power conversion efficiencies (PCE) due to undesirable morphological properties, including high aggregation and unfavorable orientation. Moreover, they show very poor long‐term stability owing to excessive molecular aggregation and unfavorable phase separation. Thus, novel p‐type polymers are required for high‐efficiency and long‐lived PSCs that can be processed in ecofriendly nonhalogenated solvents. Herein, a novel series of 1D/2A terpolymers (PBTPBD) composed of 4,8‐bis(5‐(2‐ethylhexyl)‐4‐fluorothiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT‐F), 1,3‐bis(thiophen‐2‐yl)‐5,7‐bis(2‐ethylhexyl)benzo‐[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione (BDD), and 1,3‐bis‐(4‐hexylthiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (HT‐TPD) is synthesized and characterized for high‐efficiency and long‐lived PSCs. A PBTPBD‐50:IT‐4F blended film exhibits a favorable face‐on orientation and superior hole and electron mobility. Therefore, the corresponding PBTPBD‐50:IT‐4F PSC, processed with a nonhalogenated solvent, exhibits a high PCE of 13.64%, which is 13% higher than that of the related nonhalogenated solvent‐processed PSCs. Furthermore, the PBTPBD‐50:IT‐4F PSC maintains 82% of the initial PCE even after 204 days at 85 °C, which is the highest thermal stability achieved among PSCs processed with nonhalogenated solvents. The high‐efficiency and superior long‐term thermal stability of the PBTPBD‐50:IT‐4F PSC are attributed to the excellent miscibility of PBTPBD‐50 and IT‐4F and the suppression of the morphological changes in the photoactive layer. [ABSTRACT FROM AUTHOR]

Abstract: We designed and synthesized a new low band gap donor–acceptor copolymer (PDTDPP-Oct) composed of alternating dithieno[3,2-b:2′,3′-d]thiophene and bis-thienyl-diketopyrrolo[3,4-c]pyrrole units. The polymer films showed a very broad absorption band that extended up to 950nm. Thermogravimetric analysis revealed good thermal stability and a high glass transition temperature of 128°C. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the polymer were estimated to be −5.01 and −3.70eV, respectively. Bulk heterojunction polymer solar cells were fabricated with the structure: ITO/PEDOT:PSS/polymer:PCBM/Al. The introduction of 1,8-octanedithiol as a processing additive to the polymer/PCBM blend solution significantly improved the device performance relative to devices prepared from the blend solution without the additive. This cell gave a short circuit current of −1.8mA/cm2, an open circuit voltage of 0.60V, and a fill factor of 0.52, yielding a power conversion efficiency of 0.55%. The performance improvements were mainly attributed to the fine morphology of the blend film. [Copyright &y& Elsevier]

Bodipy-based polymers, which possess a high absorption coefficient with a bandgap of ∼1.6 eV, have been used as electron donor in solution-processed bulk heterojunction (BHJ) solar cells containing PCBM as acceptor. A power conversion efficiency (PCE) of ∼2% has been achieved with Vocof ∼0.8 eV and Jscof ∼4.8 mA cm−2. [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]

Abstract: Suppression of the photocorrosion process is an important subject for quantum dot-sensitized solar cells (QSSCs). A method is reported to suppress the substitution and anodic oxidation reaction in the photocorrosion process of CdS/CdSe QSSCs through the addition of poly(ethyleneoxide) (PEO) to liquid polysulfide electrolyte. In the presence of PEO in the electrolyte, a thin PEO layer is formed on the quantum dot (QDs) film using coordination bonding between the ether group in the PEO and Cd metal ions in the QDs, acting as passivation layer to suppress substitution reaction and anodic oxidation. Due to the passivation effect of PEO thin film, the photostability of QSSCs is significantly improved compared to the liquid polysulfide electrolyte without PEO. [Copyright &y& Elsevier]

Terpolymers consisting of three monomers with one electron donor unit and two electron acceptor units are promising p-type polymers for polymer solar cells (PSCs) because the incorporation of a third monomer into a copolymer backbone provides synergetic effect on physical properties such as absorption ability, charge transport, and photovoltaic performance. Currently, novel p-type terpolymers need to be developed for high-efficiency PSCs, which can be processed with eco-friendly non-halogenated solvents. In this study, a new series of terpolymers composed of 4,8-di(2,3-didecylthiophen-5-yl)-benzo[1,2- b :4,5- b ′]dithiophene (BDT), 4,7-di(thien-2-yl)-5,6-difluoro-2,1,3-benzothiadiazole (DTffBT), and benzo[1,2- c :4,5- c ′]dithiophene-4,8-dione (BDD) segments was synthesized and characterized for high-performance PSCs processed with non-halogenated solvents. PBDTBD terpolymers (i.e., PBDTBD-25, PBDTBD-50, and PBDTBD-75) were synthesized by adjusting different ratios of DTffBT to BDD segment (25%, 50%, and 75% of DTffBT). PBDTBD terpolymers exhibited excellent solubility in non-halogenated solvents. The optical, electrochemical, and morphological properties of PBDTBD terpolymers were successfully controlled by modulating the molar ratio of DTffBT and BDD. Moreover, a PBDTBD-50:IT-4F blended film showed homogeneous film with a favorable face-on orientation. The PBDTBD-50:IT-4F blended film showed excellent hole and electron mobility, which resulted in a superior carrier balance. PBDTBD-50-based PSCs, processed with o -xylene, achieved the highest PCE of 10.03%, which is four times higher than those of copolymer-based PSCs. The novel terpolymers composed of one electron donor unit and two electron acceptor units are expected to make a considerable contribution to the development of high-performance PSCs. Image 1 • Novel terpolymers (PBDTBD) were designed and synthesized for polymer solar cells. • Physical properties of PBDTBD terpolymers were tuned by adjusting monomer ratios. • PBDTBD-50 showed favorable face-on film orientation and superior carrier mobility. • PBDTBD-50-based PSCs, processed with o -xylene, showed the highest PCE of 10.03%. [ABSTRACT FROM AUTHOR]