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The introduction of bulky substituents to the terminal unit is an effective means of tuning the solubility of non-fullerene acceptors and the morphology of blend films, and ultimately regulating the performance of organic solar cells.

Blending the donor and acceptor with a near zero HOMO offset can realize high-performance nonfullerene organic solar cells with large open circuit voltage and fill factor.

We designed and synthesized three PDI derivatives (PDI-II, PDI-III and PDI-IV). All these acceptor molecules have a central benzene core and the PDI units are linked to the central benzene core by an acetylene spacer. PDI-II is a linear molecule, which bears two flanked PDI units, PDI-III is a c3-symmetrical star-shaped molecule with three peripheral PDI units, and PDI-IV is a star-shaped molecule with four PDI units linked to the 1,2,4,5-positions of the central benzene core. These absorption features indicated that the PDI units in PDI-II and PDI-III are planar, whereas the PDI units in PDI-IV are twisted due to the steric crowding. Compared with the linear PDI-II, the star-shape could effectively prevent PDI-III and PDI-IV from forming large aggregates when blended with the donor polymer PBDB-T. PBDB-T:PDI-II, PBDB-T:PDI-III and PBDB-T:PDI-IV based OSCs gave power conversion efficiencies (PCEs) of 3.05%, 6.00% and 1.04%, respectively. The big differences in electron mobility and PCE for PDI-III and PDI-IV are probably due to the fact that the PDI units in PDI-III are planar and those in PDI-IV are twisted.

Two mutually isomeric noncovalently fused-ring electron acceptors (NC-FREAs) NOC6F-1 and NOC6F-2 containing two cyclopentadithiophene (CPDT) moieties linked at the 2,6- and 1,5-positions, respectively, of the naphthalene ring were designed and synthesized for organic solar cells (OSCs). Intramolecular noncovalent S⋯O interactions were introduced into NOC6F-1 and NOC6F-2. The tiny structural variation in NOC6F-1 and NOC6F-2 by just changing the linkage positions affects largely their molecular configuration, absorption, molecular packing, charge transport and photovoltaic performance. Compared to NOC6F-2, NOC6F-1 exhibits smaller distortions between cyclopentadithiophene and the naphthalene unit, leading to an extended conjugation and enhanced π–π stacking. NOC6F-2 exhibits a poor planarity, which restricts the electron delocalization as well as dense π–π stacking in the film form. When blended with PBDB-T, NOC6F-1 exhibits more orderly stacking along both the out-of-plane and in-plane directions than NOC6F-2. OSCs based on PBDB-T:NOC6F-2 merely showed a power conversion efficiency (PCE) of 6.74% with lower Jsc and FF values. OSCs based on NOC6F-1 achieved a higher Jsc of 17.08 mA cm−2 and an FF of 65.79%, thus leading to a significantly enhanced PCE of 10.62%. These results indicate that use of the acceptor molecules with a planar molecular backbone is an important design strategy for NC-FREAs.

A novel propeller-shaped molecule (HPB-PDI6) with a hexaphenylbenzene (HPB) core and six peripheral PDI units was synthesized via Co2(CO)8-catalyzed cyclotrimerization and used as an acceptor for organic solar cells (OSCs). The intriguing geometry of the HPB core and the spatial repulsion of the PDI rings created a twisted three-dimensional propeller-shaped conformation for HPB-PDI6. The propeller-shaped conformation could prevent the acceptor molecules from forming large aggregates in the active layer. As expected, the PTB7-Th:HPB-PDI6 blend films show a favorable morphology as well as high and balanced charge carrier mobility. Devices based on PTB7-Th:HPB-PDI6 achieved a PCE of 6.63% with a Voc of 0.92 V, a Jsc of 15.11 mA cm−2, and an FF of 48.0%. Our results have demonstrated that the easily prepared propeller-shaped HPB-PDI6 could be a promising acceptor for high efficiency organic solar cells.

To explore the influence of fluoro substitution position and number on optical, electrochemical and photovoltaic properties, three novel donor-acceptor (D-A) alternative copolymers (PHF, PFH and PFF) were synthesized by Stille polycondensation of 2,3-diphenyl-5,8-di(thiophen-2-yl)quinoxaline (DTQx) acceptor unit and indacenodithiophene (IDT) donor unit. As films, PHF and PFF comprising two fluoro substituents on the lateral phenyl groups displayed a broad absorption ranging from 350 to 700 nm; whereas PFH containing two fluorine atoms on the polymer main chain exhibited a slightly narrower absorption ranging from 350 to 650 nm. In addition, fluoro substitution on the polymer main chain can lower the HOMO level of the resulted polymers. As expected, PFH and PFF possess deeper HOMO energy level than PHF. Polymer solar cells (PSCs) were fabricated with these three polymers as donor materials and PC71BM as acceptor material. PHF based PSCs gave a power conversion efficiency (PCE) of 7.2% with a Voc of 0.84 V, a Jsc of 12.46 mA/cm2 and an FF of 0.69. And PFH based PSCs showed a PCE of 6.19% with a Voc of 0.93 V, a Jsc of 9.57 mA/cm2 and an FF 0.70. However, a PCE of only 2.9% with a Voc of 0.92 V, a Jsc of 4.61 mA/cm2 and an FF of 0.68 was obtained for PFF based PSCs. Transmission electron microscopy (TEM) and resonant soft X-ray scattering (R-SoXS) studies indicated that the introduction of four fluorine atoms at each repeating unit can spoil the morphology of active layer. These results highlight the importance of fluorination position and number to the performance of PSCs.

Novel polymers comprising a 3-fluoro-5-alkylthiophenyl benzodithiophene donor unit and a 5-fluoro-6-alkoxy (or alkylthio)-2,1,3-benzothiadiazole (BT) acceptor unit were synthesized. Both POF and PSF possess low HOMO and LUMO energy levels due to the incorporation of fluorine atoms. Additionally, alkoxy and alkylthio substitution on the BT unit also had a great influence on the molecular packing and the energy level of the resulting polymers. The introduction of the alkylthio side chains on the BT unit of PSF led to a significant downshift of the HOMO energy level in comparison to that of POF with an alkoxy substituent due to the weaker electron-donating properties of the sulfur atom than that of oxygen. However, the steric hindrance caused by the large sulfur atoms resulted in reduced planarity of the backbone of PSF, which might influence the charge transport and the morphology of the blend film. As a result, POF based NF-PSCs exhibited a PCE of 7.28%, with a Voc of 0.86 V, a Jsc of 14.9 mA cm−2, and an FF of 0.47, while a low PCE of 1.55% with a Voc of 0.95 V, a Jsc of 5.6 mA cm−2, and an FF of 0.29 was obtained for PSF based non-fullerene polymer solar cells (NF-PSCs). Therefore, the side chain engineering of the donor polymer is crucial for maximizing both Jsc and Voc values to achieve high performance polymer solar cells.

For the first time, a hyperbranched polymer acceptor, HP-PDI, was designed, synthesized and applied in polymer solar cells (PSCs). Devices based on HP-PDI showed a power conversion efficiency of 2.15%, which is 14 times higher than that of devices based on the small molecular acceptor SM-PDI. The hyperbranched structure can effectively suppress the aggregation of PDI molecules preventing them from forming large domains. Our preliminary results have demonstrated that high efficiency PSCs could be achieved by using a hyperbranched polymer acceptor.

Non-fused ring electron acceptors with varied substituents were developed to construct efficient organic solar cells (OSCs). Out-of-plane rigid substituents such as 2-methylphenyl, 2-tert-butylphenyl and diphenylamine were introduced to the central benzene unit to improve the solubility of non-fused ring acceptors and noncovalent interactions such as O⋯S and N⋯S were used to enhance the planarity of molecular backbones. Blend films based on PBDB-T and these acceptors displayed better morphology without oversized aggregates formed. As-cast devices based on SM1, SM2 and SM3 exhibited power conversion efficiencies of 5.96%, 6.43% and 6.80%, respectively.

Two donor-acceptor alternative copolymers ( P1 and P2 ) with carbazole group as the donor unit and 2,3-diphenylquinoxaline group as the acceptor unit were designed and synthesized by Suzuki polycondensation reaction. Alkoxy groups were linked to meta-position or para-position of phenyl rings, which were attached on the 2,3-position of quinoxaline group to investigate the effect of the alkoxy position at phenyl rings on the resulting polymer optical, electrochemical and photovoltaic properties. GIWAXS experiments revealed that para-substituted polymer P2 possesses closer packing properties in the solid state. The absorption spectra of para -substituted polymer P2 also displayed larger red-shift than that of meta-substituted polymer P1 when it went from solution to the film, which was beneficial to improve the hole mobilities and short circuit current density ( J sc ). When used as the donor materials, devices based on P2:PC 71 BM exhibited a PCE of 3.33%, which was obviously higher than that based on P1:PC 71 BM. Our results revealed that the slightly structure change of polymer has a significant influence on the photovoltaic properties of polymer solar cells and adopting para-substituted phenyl ring as the side groups gave superior photovoltaic performance in donor materials based on carbazole and quinoxaline.

Three novel 1,8-naphthalimide-based small molecular acceptors (NI-A-C4, NI-A-C6 and NI-A-C8) were designed and synthesized. The LUMO levels of these three small molecules were high-lying, which significantly reduce the energy loss between the wide optical band gap polymer (WBGP) PBDTBT-C12 and the acceptors and result in a high open circuit voltage (Voc) in solar cells. In addition, these three acceptors are planar, crystalline and H-aggregated in the solid state, which can facilitate the electron transport in blend films and lead to superior electron mobility and short circuit current (Jsc). A PCE of 4.05% with a Voc of 1.08 V was obtained for PBDTBT-C12:NI-A-C6-based polymer solar cells (PSCs) in an active layer thickness of 35 nm. Such a PCE is comparable to that of PBDTBT-C12:PC71BM-based optimized devices (4.07%) and better than devices with an active layer thickness of approximately 30 nm (2.72%). Besides, 35 nm is the thinnest active layer thickness for PSCs with a PCE above 4% and the absorption onset of PBDTBT-C12:NI-A-C6-blend films was as low as 630 nm, leading to a significantly high average visible transmittance up to 76.1%. Ultimately, a relatively high PCE and ultrahigh transmittance were achieved simultaneously, demonstrating that 1,8-naphthalimide-based small molecules are promising acceptors for tandem or semi-transparent PSCs.

A new low band gap polymer P1 with fluorinated acenaphtho[1,2-b]quinoxaline (AQ) as the acceptor unit and benzo[1,2-b:4,5-b′]dithiophene as the donor unit has been designed and synthesized. Comparing with its non-fluorinated analog polymer P2, P1 shows a lower band gap of 1.76 eV with a deeper HOMO energy level of −5.54 eV. Polymer solar cells with the blend of P1 and PC71BM as the active layer without the additive or annealing showed a PCE of 4.72%, which was higher than P2 based devices with a PCE of 1.65%. Obviously, P1 can endow devices with a Voc of 0.77 V and a Jsc of 10.75 mA cm−2, which are higher than that of P2 based devices with a Voc of 0.75 V and a Jsc of 4.41 mA cm−2, such an enhanced photovoltaic performance can be attributed to the broader absorption, the improvement of film morphology, and the higher charge mobility. Thus, fluorinated AQ can be a useful acceptor unit to construct narrow band gap conjugated polymers. To the best of our knowledge, this is the highest PCE report for AQ based polymer solar cells.

A novel small molecule NI-T-NI with a thiophene core and two 1,8-naphthalimide terminal groups was synthesized via direct C–H activation and used as the acceptor for polymer solar cells. NI-T-NI exhibits a good crystallinity and can form H-aggregates in the solid state. NI-T-NI has a rather high-lying LUMO level, which is beneficial for achieving a high Voc. In cooperation with a high-lying LUMO level polymer PCDTBT-C12, a PCE of 2.01% with a high Voc of 1.30 V has been achieved. As far as we know, a Voc of 1.30 V is the highest value reported for single junction organic solar cells. Our results have demonstrated that 1,8-naphthalimide could be a useful building block for the synthesis of promising acceptor materials for polymer solar cells.

Three donor–acceptor (D–A) alternating conjugated polymers with silafluorene as the donor unit, 5-alkyloxy-6-fluorobenzothiadiazole as the acceptor unit, and thiophene as the spacer has been synthesized and used as donor materials for polymer solar cells (PSCs). The introduction of a fluorine atom on the benzothiadiazole unit can lower the HOMO and LUMO energy level of the resulted polymers to afford higher open circuit voltage (Voc); whereas the introduction of a flexible alkyloxy chain on benzothiadiazole unit can increase the solubility of the resulted polymers without interfering the close packing of polymer chains in the solid state. High molecular weight polymers P-1a, P-1b, and P-1c, which are fully soluble in 1,2-dichorobenzene (DCB) at elevated temperature, have been prepared by Suzuki polycondensation. Among these polymers, P-1c exhibited the highest hole mobility up to 1.36 × 10–2 cm2 V–1 s–1. PSCs based P-1b:PC71BM demonstrated the highest Voc up to 0.98 V. P-1a:PC71BM based PSCs gave the high...

Four novel conjugated polymers (P1-4) with 9,10-disubstituted phenanthrene (PhA) as the donor unit and 5,6-bis(octyloxy)benzothiadiazole as the acceptor unit are synthesized and characterized. These polymers are of medium bandgaps (2.0 eV), low-lying HOMO energy levels (below -5.3 eV), and high hole mobilities (in the range of 3.6 × 10(-3) to 0.02 cm(2) V(-1) s(-1) ). Bulk heterojunction (BHJ) polymer solar cells (PSCs) with P1-4:PC71 BM blends as the active layer and an alcohol-soluble fullerene derivative (FN-C60) as the interfacial layer between the active layer and cathode give the best power conversion efficiency (PCE) of 4.24%, indicating that 9,10-disubstituted PhA are potential donor materials for high-efficiency BHJ PSCs.

To achieve 5,6-difluorobenzothiadiazole and 2,7-linked silafluorene based soluble conjugated polymers, flexible side chains were attached at different positions of the conjugated polymers. Three soluble polymers PSiF-D(OT)DFBT, PSiF-TTDFBT, and PDOSiF-DTDFBT were prepared and used as donor materials for polymer solar cells. PSiF-D(OT)DFBT exhibits a band gap of 2.06 eV with a deep HOMO of −5.64 eV. PSiF-TTDFBT shows a band gap of 1.75 eV with the HOMO of −5.23 eV. PDOSiF-DTDFBT is of a band gap of 1.86 eV with the HOMO level of −5.37 eV. Among these three polymers, PDOSiF-DTDFBT shows the highest field effect transistor (FET) hole mobility up to 3.31 × 10−2 cm2 V−1 s−1, PDOSiF-DTDFBT:PC71BM blend films show the highest SCLC mobility up to 5.10 × 10−4 cm2 V−1 s−1, and polymer solar cells (PSCs) with the blend of PDOSiF-DTDFBT:PC71BM (1 : 1, by weight) as the active layer gave a power conversion efficiency (PCE) of 4.03% with an open circuit voltage (Voc) of 0.73 V, a short circuit current (Jsc) of 8.55 mA cm−2, and a fill factor (FF) of 0.65. Our studies also reveal the structure–property relationship of 2,7-linked silafluorene and 5,6-difluorobenzothiadiazole based conjugated polymers.

The synthesis, characterization, and photophysical and photovoltaic properties of two anthracene-containing wide-band-gap donor and acceptor (D-A) alternating conjugated polymers (P1 and P2) are described. These two polymers absorb in the range of 300-600 nm with a band gap of about 2.12 eV. Polymer solar cells with P1:PC71 BM as the active layer demonstrate a power conversion efficiency (PCE) of 2.23% with a high Voc of 0.96 V, a Jsc of 4.4 mA cm(-2) , and a comparable fill factor (FF) of 0.53 under simulated solar illumination of AM 1.5 G (100 mW cm(-2) ). In addition, P2:PC71 BM blend-based solar cells exhibit a PCE of 1.42% with a comparable Voc of 0.89 V, a Jsc of 3.0 mA cm(-2) , and an FF of 0.53.

Four ethynylene-containing donor-acceptor alternating conjugated polymers P1–P4 with 2,5-bis(dodecyloxy) substituted phenylene or carbazole as the donor unit and benzothiadiazole (BTZ) as the acceptor unit were synthesized and used as donor polymers in bulk heterojunction polymer solar cells. The optical, electrochemical, and photovoltaic properties of these four polymers with the ethylene unit located at different positions of the polymer chains were systematically investigated. Our results demonstrated that absorption spectra and the HOMO and LUMO energy levels of polymers could be tuned by varying the position of the ethynylene unit in the polymer chains. Photovoltaic devices based on polymer/PC71BM blend films spin coated from chloroform and dichlorobenzene solutions were investigated. For all four polymers, open circuit voltages (Voc) higher than 0.8 V were obtained. P4, with ethynylene unit between BTZ and thiophene, shows the best performance among these four polymers, with a Voc of 0.94 V, a Jsc of 4.2 mA/cm2, an FF of 0.40, and a PCE of 1.6%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Three D–A alternating copolymers P1–3 with 3,7-linked 2,8-bis(alkoxy)dibenzothiophene as the donor unit and benzothiadiazole (P1 and P2) or 3,4-bis(octyloxy)benzothiadiazole (P3) as the acceptor unit have been designed and synthesized. P1–3 show two broad absorption peaks in the visible region, and the internal charge transfer (ICT) absorptions at about 530 nm in solutions and 560 nm in films of P3 are much stronger than that of P1 and P2. All the polymers show narrow band gaps below 2.0 eV and the low-lying HOMO energy levels of approximately −5.30 eV. The hole mobilities of polymer films spin-cast from 1,2-dichlorobenzene (DCB) solutions are 3.0 × 10–4, 2.7 × 10–4, and 2.3 × 10–3 cm2 V–1 s–1 for P1, P2, and P3, respectively. Under simulated solar illumination of AM 1.5G (100 mW/cm2), a PCE of 4.48% with a Voc of 0.83 V, a Jsc of 9.30 mA/cm2, and an FF of 0.58 has been achieved for PSCs with the P3:PC71BM blend (1:3, by weight) as the active layer in simply processed devices, whereas after the optimizati...

A new alternating copolymer (PSFDTBT) based on spirobifluorene, thiophene, and benzothiadiazole units has been synthesized. PSFDTBT has an optical band gap of 1.97 eV with the low-lying HOMO energy level at −5.4 eV. The hole mobility of the pristine PSFDTBT film spin-cast from o-dichlorobenzene (DCB) solution is 7.26 × 10–3 cm2 V–1 s–1 with on/off ratios in the order of 105. Polymer solar cell devices based on the blend films of PSFDTBT and PC71BM show a high open-circuit voltage of 0.94 V and a power conversion efficiency of 4.6% without any post-treatment. All the device measurements were performed in air without encapsulation. This is the first report on spirobifluorene-based conjugated polymers used for polymer solar cells, demonstrating the great potential of spirobifluorene moiety as an electron-donating unit for the construction of main chain donor–acceptor alternating conjugated polymers for high performance polymer solar cells.

A series of donor-acceptor (D-A) alternating copolymers (P1, P2 and P3) with thiophene -benzothiadiazole-thiophene-triphenylamine main chain have been synthesized by Suzuki poly-condensation. P1, P ...

A new 1,8-naphthalimide based planar small molecular acceptor and two benzothiadiazole based wide band gap (WBG) polymer donors P1 and P2 were synthesized for nonfullerene organic photovoltaic cells (OPVs). Devices based on fluorinated polymer P2 achieved a highly improved PCE of 3.71% with an open circuit voltage (V(oc)) of 1.07 V, which is beyond the currently known levels for nonfullerene OPVs with the V(oc) higher than 1 V.

A novel donor-acceptor copolymer containing 9-alkylidene-9H-fluorene unit in the main chain, poly[9-(1-hexylheptylidene)-2,7-fluorene-alt-5, 5-(4,7-di-2-thienyl-5,6-dialkoxy-2,1,3-benzothiadiazole) ...

Silole-containing conjugated polymers (P1 and P2) carrying methyl and octyl substituents, respectively, on the silicon atom were synthesized by Suzuki polycondensation. They show strong absorption in the region of 300–700 nm with a band gap of about 1.9 eV. The two silole-containing conjugated polymers were used to fabricate polymer solar cells by blending with PC61BM and PC71BM as the active layer. The best performance of photovoltaic devices based on P1/PC71BM active layer exhibited power conversion efficiency (PCE) of 2.72%, whereas that of the photovoltaic cells fabricated with P2/PC71BM exhibited PCE of 5.08%. 1,8-Diiodooctane was used as an additive to adjust the morphology of the active layer during the device optimization. PCE of devices based on P2/PC71BM was further improved to 6.05% when a TiOx layer was used as a hole-blocking layer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

In this feature article, we present a short review on the recent development in the construction of structurally perfect red and blue light-emitting materials and highlight such research in our group. We focus mainly on the three-dimensional conjugated structures such as dendrimers, hyperbranched polymers, star polymers, spirobifluorene-based polymers, and spiro-bridged ladder-type oligomers and polymers. Results indicated three-dimensional conjugated structures can efficiently decrease the aggregation of materials, resulting in the improving of the light-emitting efficiency.

A series of main chain donor-acceptor low-bandgap conjugated polymers were designed, synthesized, and used for the fabrication of polymer solar cells. The absorption spectra of low-bandgap conjugated polymers were tuned by the ratio of three copolymerization monomers. The polymers in films exhibited broad absorption ranging from 300 to 1000 nm with optical bandgaps of around 1.40 eV. All of the polymers have been investigated as an electron donor in photovoltaic cells blending with PCBM ([6, 6]-phenyl C61-butyric acid methyl ester) as an electron acceptor and power conversion efficiencies (PCEs) of 1.32–1.8% have been obtained. As for P1, PCE increases from 1.67 to 2.44% after adding 1,8-diiodooctance as an additive. The higher PCEs are probably because of better phase separation of blend films. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2571–2578, 2010

A series of polythiophene derivatives P1-P5 containing carbazole side chains were designed and synthesized via the Stille polymerization. All carbazole containing polymers showed broad absorption in the visible region. The power conversion efficiencies of solar cells based on blends of two component copolymers and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) were determinedto be0.29 and0.56% for P1and P5,respectively. For solarcells fabricated with the three component copolymers and PC61BM, the efficiencies were 0.56% for P2, 0.86% for P3, and 0.70% for P4. The introduction of electrondonating carbazole side chains can broaden the absorption in the visible region and meanwhile reduce phase separation due to the steric hinderance of the carbazole moiety to the conjugated main chain. Improving efficiency needs a balance of broad absorption and ordered packing of polymer chains in the solid state.

Polyacetylenes, poly(p-phenyleneethynylenes), and polydiacetylenes, as conjugated polymers derived from triple-bond containing building blocks, attain considerable attention because of their electronic and photoconduction properties. In this review, recent studies on the design and synthesis of conjugated polymers derived from triple-bond building blocks are summarized with an emphasis on the developments in our group in recent years. Our intense attention is focused on constructing different molecular systems with enhanced light-harvesting efficiency, and determining the functional properties of conjugated organic polymers. The conjugated organic polymers that appear in this review are useful candidates for various potential applications because of their extraordinary optical and electronic properties. The potential applications of the conjugated polymer-containing systems are explored.

A new poly(p-phenylene ethynylene) derivative with pendant 2,2′-bipyridyl groups and glycol units (PPE-bipy) has been prepared, and its metal ion sensing properties were investigated. The polymer of PPE-bipy exhibited high selectivity for Hg2+ as compared with Li+, Na+, K+, Ba2+, Ca2+, Mg2+, Al3+, Mn2+, Ag+, Zn2+, Pb2+, Ni2+, Cd2+, Cu2+, Co,2+ and Fe3+ in THF/EtOH (1:1, v/v) solution. The fluorescence of PPE-bipy was efficiently quenched by Hg2+ ions, and the detection limit was found to be 8.0 nM in a THF/EtOH (1:1, v/v) solvent system. PPE-bipy also showed a selective chromogenic behavior toward Hg2+ ions by changing the color of the solution from slight yellow to colorless, which can be detected with the naked eye. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1998–2007, 2008

The nonlinear absorptions and nonlinear refractions of free-base porphyrin (P2) and Zn-porphyrin (ZnP2) were studied using the Z-scan technique at 532 nm with different pulse durations. Both P2 and ZnP2 exhibit reverse saturated absorption attributed to excited-state absorption. The coordination of P2 by Zn ion can alter the nonlinear refraction sign from negative to positive at 4 ns pulse. The results indicate that the sign of self-lensing can be tuned by the coordination of Zn in the porphyrin derivatives. In the case of longer pulse duration, the thermal effect was enhanced to dominate the nonlinear refraction sign, leading to the negative nonlinear refraction repeated appearance.

An ultrathin composite film containing cationic tetra-pyridine perylene tetracarboxylic acid diimide (TPP-I) and an anionic tetra-sulfuric perylene tetracarboxylic acid diimide (TSP-Na) has been fabricated by the electrostatic layer-by-layer self-assembly technique. UV/Vis spectra showed a continuous and uniform deposition process of TPP-I/TSP-Na. The film structure was characterized by the small-angle X-ray diffraction measurement and atomic force microscopy image. We investigated the third-order nonlinearity of the ultrathin film sample at 532 nm. The film exhibited strong saturable nonlinear absorption. The nonlinear absorption coefficient and refractive index of the film sample are − 5.0 × 10 − 7 mW − 1 and − 1.2 × 10 − 14 m 2 W − 1 , respectively.

A new amphiphilic polymer containing pyridine units was synthesized and characterized. The solvent-dependent conformational transition from extended transoid to helical cisoid was studied by absorption, fluorescence, and 1H NMR measurements. The polar solvent promoted the formation of the helical structures. A metal ion or H+ could stabilize the ordered structure. Moreover, the solvophobically induced helical structure was stable to environmental stimuli. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1403–1412, 2007.

A series of oligo(phenylenevinylene)s (OPVs) of different lengths containing aldehyde and dialdehyde groups on the ends were synthesized and characterized. Their photophysical properties were also investigated via ultraviolet–visible, steady-state, and time-resolved fluorescence spectra. The results indicated that the absorption maximum, radiative rate constant, and excitation maximum of an OPVnCHO oligomer series (where n represents the oligomeric length) showed linear relationships with the reciprocal number of conjugated units. Similarly, the absorption maximum and emission lifetime of the oligomers of an OPVn–2CHO series showed linear relationships with the reciprocal number of conjugated units. The dependence of the fluorescence intensities of the OPVs on the concentration of the quencher C60 was evaluated. Apparently, upon photoexcitation, the OPVs underwent significant fluorescence quenching. The results for different OPV derivatives and a quenching mechanistic discussion showed that the static quenching contribution was indeed responsible for the significant upward curvature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 911–924, 2007

Performance enhancement of polymer solar cells (PSCs) is achieved by expanding the absorption of the active layer of devices. To better match the spectrum of solar radiation, two polymers with different band gaps are used as the donor material to fabricate ternary polymer cells. Ternary blend PSCs exhibit an enhanced short-circuit current density and open-circuit voltage in comparison with the corresponding HD-PDFC-DTBT (HD)- and DT-PDPPTPT (DPP)-based binary polymer solar cells, respectively. Ternary PSCs show a power conversion efficiency (PCE) of 6.71%, surpassing the corresponding binary PSCs. This work demonstrates that the fabrication of ternary PSCs by using two polymers with complementary absorption is an effective way to improve the device performance.

A series of new polymers containing porphyrin, poly(p-phenylenevinylene) (PPV), and/or a pendant fullerene unit has been synthesized. The cyclic voltammetry showed us a good candidate for a photoinduced electron-transfer system. More important, the photocurrent measurement revealed an interesting phenomenon that the photocurrent increased with the contents of the fullerene in the polymers increased. SEM images displayed the aggregation superstructures of three polymers. Nanobriquetting, nanofiber, and hierarchical porous structure were observed, respectively. The results indicated that the axial coordination of metal porphyrin and Bipy was very important to control the aggregation morphologies of the polymers.

High-molecular-weight conjugated polymer HD-PDFC-DTBT with N-(2-hexyldecyl)-3,6-difluorocarbazole as the donor unit, 5,6-bis(octyloxy)benzothiadiazole as the acceptor unit, and thiophene as the spacer is synthesized by Suzuki polycondensation. HD-PDFC-DTBT shows a large bandgap of 1.96 eV and a high hole mobility of 0.16 cm(2) V(-1) s(-1) . HD-PDFC-DTBT:PC71 BM-based inverted polymer solar cells (PSCs) give a power conversion efficiency (PCE) of 7.39% with a Voc of 0.93 V, a Jsc of 14.11 mA cm(-2) , and an FF of 0.56.

We have studied the self-assembly of two aromatic thiols, 4-mercaptopyridine (4MPY ) and 4-hydroxythiophenol (4HTP), on Au(111) from aqueous solutions with in situ scanning tunneling microscopy and ex situ X-ray photoelectron and Auger electron spectroscopies. Upon adsorption of the molecules, islands of nanometer scale appear immediately on flat Au(111) terraces, which is in sharp contrast to the formation of depressions in the selfassembly of the n-alkanethiol monolayers. The islands increase both in size and number initially, and decrease slowly after reaching maximum values in about 15 min. The formation of the islands can be attributed to the Au atoms on the surface which become highly mobile due to the strong binding to the thiols. The decrease of the islands at the late stage is due to the fact that atoms in small islands diVuse into nearby big islands and surface step edges. Both 4MPY and 4HTP molecules are randomly distributed on the surface immediately after adsorption, but slowly arrange into domains of ordered structures. For 4MPY the ordered structure has lattice constants, a=5.1±0.3 A ˚ , b=

The self-assembly of 1,10′ phenanthroline (phen) on Au(111) from aqueous solutions has been studied as a function of the substrate potential with in situ scanning tunneling microscopy (STM). The phen molecules adsorb spontaneously onto the substrate with a preference to decorate the reconstruction stripes of Au(111). The adsorbed molecules stand vertically with their nitrogen atoms facing the Au(111) and stack, like rolls of coins, into polymer-like chains. At high potentials, the chains pack closely in parallel and form an ordered monolayer. Decreasing the potential to a critical value, the chains become randomly oriented via a reversible order-disorder phase transition that resembles the nematic-isotropic transition in liquid crystal materials. High resolution images reveal each phen molecule as two blobs located at the two nitrogen atoms, indicating that the coupling between the nitrogen atoms and Au(111) is responsible for the tunneling current probed by STM. The phen monolayer contains pits with a depth of about one Au layer, which may be attributed to surface stress induced by the strong adsorption of the phen molecules on the surface.

Stepwise locking of phenyl rings of tetraphenylethene increases the emission efficiency of luminogen solutions gradually, thus verifying the restriction of intramolecular rotation (RIR) mechanism of the aggregation induced emission phenomenon. The emission of the luminogen with one “O” bridge could be tuned reversibly in solid state through repeated heating and grinding.

Dihydronaphthyl-based [60]fullerene bisadduct derivative, NC(60)BA, was synthesized at mild temperature in high yield. NC(60)BA not only possesses a LUMO energy level 0.16 eV higher than PC(61)BM but also has amorphous nature that can overcome thermal-driven crystallization. The fabricated P3HT:NC(60)BA-based polymer solar cells exhibit superior photovoltaic performance and thermal stability compared to PC(61)BM-based devices under the same conditions.

Emission of a luminogen could be switched among three colors in the solid state by transformation among three different aggregation states. The partly amorphous solid of the luminogen exhibits excitation dependent emission due to the contribution of both amorphous and crystalline parts to the photoluminescence intensity.