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Preparing polymer nanowire (PNW) structures using donor–acceptor (D–A) conjugated polymers is one promising strategy to improve the power conversion efficiencies (PCEs) of bulk-heterojunction (BHJ) polymer solar cells (PSCs). Here, we report that a high PCE of 10.62% was obtained with a single-junction inverted cell with a 350 nm thick active layer containing highly crystalline PNWs based on a D–A conjugated polymer (P4TNTz-2F), which possesses a deep-lying HOMO level (−5.46 eV) and a low-bandgap (1.59 eV) as well as a planar/rigid backbone. The thick active layer in the P4TNTz-2F : PC71BM-based PSC absorbs incident light almost completely, which in turn contributes to a high short-circuit current density of 19.45 mA cm−2. This high PCE is attributed to the continuous and evenly distributed polymer network with narrow PNWs (≈6 nm in width and several hundred nanometers in length) in the thick film blended with PC71BM, which facilitates charge separation (QPL ≈ 98%) and transport (μh = 8.31 × 10−3 cm2 V−1 s−1). Moreover, this PNW structure in the BHJ active layer can be prepared using a facile film-forming process at a mild blending temperature (≈70 °C), which means that high efficiency BHJ PSCs can be fabricated with good reproducibility. These results demonstrate the great promise of polymer nanowire solar cells and provide important scientific insights that facilitate further improvements in the morphologies and performances of organic solar cells through material design and development.

The position at which conjugated side chains were fluorinated, the meta- or ortho-position in phenyl side chains, was varied to investigate the positional effects of fluorination on the energy levels, crystalline ordering, and photovoltaic properties of the polymers. The fluorine in the ortho-position achieved a lower HOMO energy level than that in the meta-position, but reduced the chain rigidity.

The synergistic effects of a thiophene-based π-bridging backbone extension on the intrinsic and photovoltaic properties of electron donor–acceptor (D–A) copolymers were systematically investigated. A series of alternating D–A copolymers (PBTs) based on 4,8-bis(5-ethylhexylselenophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene (EHSeBDT) and 5-(2-butyloctyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (BOTPD), which featured thiophene-based π-bridges, were synthesized: PBT without a π-bridge, PBT with a 3-octylthiophene (OT) π-bridge (PBT-OT), and PBT with a 3-octylthieno[3,2-b]thiophene (OTT) π-bridge (PBT-OTT). The light absorption and charge transport properties were significantly enhanced upon incorporation of the OTT π-bridge. The enhancements resulted from the strong π–π intermolecular interactions using the OTT π-bridging backbone extension between neighboring polymer chains. PBT-OTT was most miscible in PC71BM. As a result, the photoactive layers prepared using PBT-OTT and PC71BM formed a well-mixed bulk-heterojunction morphology and yielded organic solar cells (OSCs) with a high power conversion efficiency of 7.21%. Transient absorption analysis suggested that the π-electrons were further delocalized along the copolymer after incorporation of the OTT π-bridge, and the charge separation efficiency increased. These results suggested that incorporating OTT π-bridges into D–A copolymers provides a useful strategy for developing highly efficient OSCs.

The control of the molecular energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is crucial to the design of highly efficient polymer solar cells (PSCs). In particular, the fine control of the HOMO energy level is vital because it can ensure that polymer solar cell devices have a high open circuit voltage (Voc) and a high short circuit current density (Jsc). We systematically synthesized a series of polymers substituted with different numbers of fluorine (F) atoms in conjugated side chains to fine-tune the HOMO energy levels of the donor polymer, and then optimized the associated solar cell devices by varying the length of the alkyl chain in the conjugated side chains. A series of conjugated side chains with non-fluorinated (0F), mono-fluorinated (1F), and di-fluorinated (2F) alkoxyphenyl groups at the meta position were synthesized and introduced into the donor polymer. The strong electron-withdrawing properties of fluorine were found to reduce the HOMO energy level and yield high Voc values up to 1.01 V. The substitution of the conjugated side chain with fluorine affects not only the energy level of the polymer but also its intermolecular packing and crystallinity due to the resulting intermolecular interactions, and was found to be effective in the control of Jsc and FF. A maximum efficiency of 7.64% was achieved for the polymer with the mono-fluorinated conjugated side chain.

We designed, synthesized, and characterized a series of three medium-bandgap conjugated polymers (PBDTfDTBO, PBDTfDTBT, and PBDTfDTBS) consisting of fused dithienobenzochalcogenadiazole (fDTBX)-based weak electron-deficient and planar building blocks, which possess bandgaps of ∼2.01 eV. The fDTBX-based medium-bandgap polymers exhibit deep-lying HOMO levels (∼5.51 eV), which is beneficial for use in multijunction polymer solar cell applications. The resulting polymers with chalcogen atomic substitutions revealed that the difference in the electron negativity and atomic size of heavy atoms highly affects an intrinsic property, morphological feature, and photovoltaic property in polymer solar cells. The polymer solar cells based on sulfur-substituted medium-bandgap polymer showed power conversion efficiencies above 6% when blended with [6,6]-phenyl-C71-butyric acid methyl ester in a typical bulk-heterojunction single cell. These results suggest that the fDTBX-based medium-bandgap polymer is a promising alter...

Fine tuning the energy levels of donor polymers is a critically important step toward achieving high power conversion efficiencies in polymer solar cells (PSCs). We systematically controlled the energy levels of donor polymers by introducing cyano (CN) and alkoxy (OR) groups into the 4,4′-didodecyl-2,2′-bithiophene (BT) unit in a step-by-step fashion, thereby varying the inductive and resonance effects. The three monomer units (BT, BTC, and BTCox) were polymerized with benzo[1,2-b:4,5-b′]dithiophene (BDT) as a counter unit to afford three polymers (PBDT-BT, PBDT-BTC, and PBDT-BTCox). The highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels decreased significantly upon the introduction of CN groups, and these levels increased slightly upon attachment of the OR groups, in good agreement with the measured open-circuit voltages of the three polymer devices. The strong inductive and resonance effects present in PBDT-BTCox narrowed the polymer band gap to 1.74 eV to afford a ...

Two donor-acceptor copolymers, PBDT and PNDT, containing 4,8-bis(2-ethylhexyloxy)benzo[1,2-b:3,4-b']dithiophene (BDT) and 4,9-bis(2-ethylhexyloxy)naphtho[1,2-b:5,6-b']dithiophene (NDT), respectively, as an electron-rich unit and 5,6-difluoro-2,1,3-benzothiadiazole (2FBT) as an electron-deficient unit, were synthesized and compared. The introduction of the NDT core into the conjugated backbone was found to effectively improve both light harvesting and the charge carrier mobility by enhancing chain planarity and backbone linearity; the NDT copolymer has stronger noncovalent interactions and smaller bond angles than those of the BDT-based polymer. Moreover, the introduction of the NDT core brings about a drastic change in the molecular orientation into the face-on motif and results in polymer:PCBM blend films with well-mixed interpenetrating nanofibrillar bulk-heterojunction networks with small-scale phase separation, which produce solar cells with higher short-circuit current density and fill factor values. A conventional optimized device structure containing PNDT:PC71BM was found to exhibit a maximum solar efficiency of 6.35%, an open-circuit voltage of 0.84 V, a short-circuit current density of 11.92 mA cm(-2), and a fill factor of 63.5% with thermal annealing, which demonstrates that the NDT and DT2FBT moieties are a promising electron-donor/acceptor combination for high-performance photovoltaics.

A series of two-dimensional conjugated polymers containing π-conjugated oligothienyl side chains, namely PBDT2FBT-T1, PBDT2FBT-T2, PBDT2FBT-T3, and PBDT2FBT-T4, was designed and synthesized to investigate the effect of two-dimensionally extended π-conjugation on the polymer solar cell (PSC) performance. The oligothienyl units introduced into the side chains significantly affect the optoelectronic properties of the parent polymers as well as the performances of the resulting solar cell devices by altering the molecular arrangement and packing, crystalline behavior, and microstructure of the polymer:PC71BM blend films. The crystallinity and blend morphology of the polymers can be systematically controlled by tuning the π-conjugation length of side chains; PBDT2FBT-T3 exhibited the most extended UV/vis light absorption band and the highest charge mobility, leading to a high short-circuit current density up to 12.5 mA cm–2 in the relevant PSCs. The PBDT2FBT-T3:PC71BM-based PSC exhibited the best power convers...

Understanding the microstructures of semiconducting polymers is critical for improving the charge transport properties of polymer field-effect transistors (PFETs). A series of diketopyrrolopyrrole-based copolymers designed by implementing the concept of intramolecular noncovalent conformational locks through the functionalization of polymer backbones with fluorine atoms or methoxy groups were synthesized and compared with their unfunctionalized analogue. In contrast to the bimodal texture of the unfunctionalized polymer, the thin films of the polymer with fluorine atoms exhibit predominantly edge-on texture with much improved crystalline ordering. The thin films of the polymer modified with methoxy groups have a principally face-on texture. These dramatic differences in thin-film texture can be correlated with the polymers’ solubilities. Furthermore, the improved crystalline ordering of these semiconductor polymers enables the fabrication of high-performance PFETs: the hole mobility of the methoxy-modifie...

A series of pentacene derivatives with unsaturated hydrocarbon substituents at the 6,13-positions as side groups have been synthesized. The effects of conjugated π-bonding throughout the side groups on the solubility, oxidative stability, crystallinity, and electrical properties of the compounds were investigated. Here we report that the solubility of pentacene can be greatly improved by the insertion of linear long side groups at the 6,13-positions: the obtained pentacene derivatives were soluble in common organic solvents. Time-dependent UV-visible spectra in chloroform solutions as well as thin films were recorded to investigate the oxidative stability of each pentacene compound under ambient conditions. The photooxidative stability of the pentacene derivatives was remarkably enhanced by increasing the electron conjugation length through the installation of unsaturated hydrocarbon substituents at the 6,13-positions. The solution-processed TFT devices based on 6,13-bis(4-pentylphenyl-ethynyl)pentacene (P5) and 6,13-bis(4-hexylphenylethynyl)pentacene (P6) showed charge transport mobilities of 2.14 × 10−2 cm2 V−1 s−1 and 3.94 × 10−2 cm2 V−1 s−1, respectively, and exhibited an on/off ratio of 105. Here we demonstrate that P5 and P6 revealed much more stable electrical performances than the parent pentacene under the oxidative environment.

Introducing conjugated side chains onto the backbone of two-dimensionally (2D) conjugated polymers has been utilized for tuning the optoelectronic characteristics of the polymer and the morphological properties of organic photovoltaics. To investigate the effects of conformational symmetry of conjugated side chains, two benzo[1,2-b:3,4-b′]dithiophene (BDT)-based derivatives, one with the asymmetric alkoxythienyl (Th) side chain and the other with the symmetric alkoxyphenyl (Ph) side chain, were synthesized as donor units and copolymerized with fluorinated benzothiadiazole (2FBT). These two side chains were selected for the distinct differences between their structures, and were found to affect the intrinsic characteristics of these BDT polymers. The introduction of the symmetric conjugated side chain to the conjugated backbone of the polymer was observed to improve both light harvesting and the charge carrier mobility, apparently by increasing the extent of packing between the polymer chains. Power conversion efficiency (PCE) values of photovoltaic devices fabricated using these conjugated polymers were strongly related to the light absorbance and crystallinity in a film of the blend of polymer and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM). PBDT2FBT-Ph showed effective light absorption, an optimum morphology that we argue is due to the symmetry of the conjugated Ph side chain, and a maximum PCE of 6.23%, with an open-circuit voltage of 0.83 V, a short-circuit current density of 11.33 mA cm−2, and a fill factor of 66.3%. These results demonstrate that symmetric conjugated side chains are promising groups to produce 2D-conjugated polymers for high-performance photovoltaics. This systematic study of side chain engineering provides a valuable strategy to synthesize 2D conjugated polymers and to achieve high PCE values in organic photovoltaics.

In this study, 6,13‐Bis(4‐propylphenyl)pentacene was synthesized and characterized. The structures of the products that were obtained during the reaction steps were identified via FT‐IR and NMR spectroscopy and elemental analysis. The compound was found to be soluble in organic solvents like chloroform, dichloromethane, THF, and toluene. The charge transport mobility was 10‐4 cm2V‐1s‐1, and the on/off current ratio was 102, while the compound was 2.5 times more stable under oxidation in a solution compared with pentacene.

A new 3D nonfullerene small-molecule acceptor is reported. The 3D interlocking geometry of the small-molecule acceptor enables uniform molecular conformation and strong intermolecular connectivity, facilitating favorable nanoscale phase separation and electron charge transfer. By employing both a novel polymer donor and a nonfullerene small-molecule acceptor in the solution-processed organic solar cells, a high-power conversion efficiency of close to 6% is demonstrated.

A donor-acceptor conjugated copolymer enables the formation of nanowire systems that can be successfully introduced into bulk-heterojunction organic solar cells. A simple binary solvent mixture that makes polarity control possible allows kinetic control over the self-assembly of the crystalline polymer into a nanowire structure during the film-forming process. The enhanced photoconductivity of the nanowire-embedded photoactive layer efficiently facilitates photon harvesting in the solar cells. The resultant maximum power conversion efficiency is 8.2% in a conventional single-cell structure, revealing a 60% higher performance than in devices without nanowires.

Interfacial energetics determines the performance of organic photovoltaic (OPV) cells based on a thin film of organic semiconductor blends. Here, an approach to modulating the “carrier selectivity” at the charge collecting interfaces and the consequent variations in the nongeminate charge carrier recombination dynamics in OPV devices are demonstrated. A ferroelectric blend interfacial layer composed of a solution-processable ferroelectric poly­mer and a wide bandgap semiconductor is introduced as a tunable electron selective layer in inverted OPV devices with non-Ohmic contact electrodes. The direct rendering of dipole alignment within the ferroelectric blend layer is found to increase the carrier selectivity of the charge collecting interfaces up to two orders of magnitude. Transient photovoltaic analyses reveal that the increase of carrier selectivity significantly reduces the diffusion and recombination among minority carriers in the vicinity of the electrodes, giving rise to the 85% increased charge carrier lifetime. Furthermore, the carrier-selective charge extraction leads to the constitution of the internal potential within the devices, even with energetically identical cathodes and anodes. With these carrier-selectivity-controlled interlayers, the devices based on various photoactive materials commonly display significant increments in the device performances, especially with the high fill factor of up to 0.76 under optimized conditions.

Oncogenic Ras is known to drive both the Rac and Raf-MAP-kinase pathways, which act in concert to cause cell transformation. Unlike the Raf-MAP-kinase cascade, however, the downstream elements of Rac pathway are not fully understood. Previously, we showed that cytosolic phospholipase A2 (cPLA2) and subsequent metabolism of arachidonic acid act downstream of Rac to mediate the transformation signaling induced by Ha-Ras(V12). In the present study, we observed that leukotriene B4 (LTB4) and its synthetic enzymes as well as BLT2, the low-affinity LTB4 receptor, are all elevated in Ha-Ras(V12)-transformed cells. In addition, the malignant phenotypes of Ras-transformed cells were markedly inhibited by BLT2 blockade, as was their tumorigenicity in vivo. Finally, in situ hybridization analysis revealed that expression of BLT2 is significantly upregulated in a variety of human cancers. Taken together, our results suggest that an LTB4-BLT2-linked cascade plays a crucial mediatory role in the cell transformation induced by oncogenic Ha-Ras(V12), possibly acting downstream of Rac-cPLA2.

DOI: 10.1002/aenm.201400087 These specifi c design criteria promote high values of the short-circuit current ( J sc ), the open-circuit voltage ( V oc ), and the fi ll factor (FF) of PSCs, which are all related to the PCE. Therefore, tremendous effort has been devoted to optimizing these key parameters by developing new molecular structures and consequently several design rules have been proposed so far. [ 10 ]

We report the preparation of a new acceptor unit, 3-alkoxy-4-cyanothiophene, and a 3-alkoxy-4-cyanothiophene-based low band-gap polymer (PBDT–CT) with a deep HOMO energy level (−5.5 eV). A bulk heterojunction solar cell containing PBDT–CT and PC61BM was found to exhibit a high open circuit voltage (Voc) of 0.90 V and an efficiency of 3.36%.

Two benzo[1,2-b:4,5-b′]dithiophene (BDT) derivatives with conjugated substituents, triisopropylsilylethynyl (TIPS) and 4-octylphenylethynyl groups, were synthesized as donor units (D) and copolymerized with two acceptor units (A), 4,7-bis(4-octylthiophen-2-yl)-2,1,3-benzothiadiazole (BT) and 4,4′-diundecyl-2,2′-bithiazole (BTZ), respectively, using Stille coupling reaction to afford four new copolymers, PTBDT-BT, PTBDT-BTZ, POPEBDT-BT, POPEBDT-BTZ. All polymers exhibited highest occupied molecular orbital (HOMO) energy levels that were deeper than −5.4 eV due to the conjugated substituents. Small band gaps were successfully achieved for PTBDT-BT (1.67 eV) and POPEBDT-BT (1.67 eV) and were attributable to the strong intramolecular charge transfer within the D–A alternating structure. The resultant photovoltaic performances showed high open-circuit voltages (Voc) ranging from 0.73 V to 0.92 V, whereas the power conversion efficiencies (PCEs) depended strongly on the blend morphologies. The polymer solar cell based on the blend of PTBDT-BT and PC71BM gave the best photovoltaic performance among the series, with a high Voc of 0.81 V and a PCE of 4.61%.