Synthesis and Photovoltaic Properties of Polythiophene Incorporating with 3,4-Difluorothiophene Units

Two polythiophene derivatives using fluorine atoms and hexyl or hexyloxy group as electron-withdrawing and donating substituents have been synthesized. The introduction of fluorine atoms to the polythiophene backbones simultaneously lowers the HOMO and narrows the bandgap, and the stronger electron-donating ability of hexyloxy side chain further reduces the bandgap. As a result, poly[3-hexylthiophene-2,5-diyl-alt-3,4-difluorothiophene] （PHTDFT） shows HOMO and bandgap of -5.31/1.83 eV and poly[3,4-dihexyloxythiophene-2,5-diyl-alt-3,4-di- fluorothiophene] （PDHOTDFT） shows HOMO and bandgap of -5.14/1.68 eV, both are lower than --4.76/2.02 eV of P3HT. Benefiting from the lower HOMO, PHTDFT：PC61BM （1 ＂ 1） polymer solar cells obtain a power conversion efficiency of 1.11% and an impressed open-circuit voltage of 0.79 V under solar illumination AM1.5 （100 mW/cm2）.     

Donor-Acceptor Oligomers and Polymers Composed of Benzothiadiazole and 3-Hexylthiophene： Effect of Chain Length and Regioregularity

A series of donor-acceptor oligomer OBTThn （n = 1- 7） and polymer PBTThl and PBTTh2 composed of al- ternative 2,1,3-benzothiadiazole and 3-hexylthiophene have been designed and synthesized for the purpose of in- vestigation on the effect of chain length and side-chain regioregularity on their basic properties and photovoltaic performance. In the OBTThn oligomers and PBTThl polymer, all the hexyl side chains on thienyl units orient to- ward the same direction. Upon elongation of the chain length, the intramolecular charge transfer （ICT） absorption band in solution gradually redshifts from 398 nm for OBTThl to 505 nm for OBTThT, then to 512 nm for PBTThl polymer. Meanwhile, the HOMO energy level increases from -5.45 eV （OBTTh0 to -5.08 eV （OBTThT） and -5.09 eV （PBTThl）, and the LUMO energy level decreases from -3.11 eV （OBTTh0 to -3.30 eV （OBTThT） and -3.33 eV （PBTThl）, thus giving a smaller and smaller energy bandgap for higher oligomers and polymers. Theo- retical calculation suggests straight line-like backbone geometry for this series of oligomers and polymer. On the other hand, polymer PBTTh2 possesses a different side-chain regioregularity, in which every two neighbor hexyl side chains are arranged in different orienting direction. It is theoretically suggested to have curved line-like back- bone geometry. In solution, it shows similar photophysical and electrochemical properties as PBTThl. However in film state, it displays a less redshift in the ICT band as refer to that in solution than PBTThl. In combination with [6,6]-phenyl-C61-butyric acid methyl ester （PC61BM）, these oligomers and polymers were used as donor material to fabricate organic bulk heterojunction solar cells. Again, chain length-dependent device photovoltaic performance was observed. The device based on OBTTh4 showed a power conversion efficiency of 0.16%, while it increased to 0.36% and 0.49% for the devices based on OBTTh6 and PBTThb respectively. However, the side-chain regio- regularity has less influence on the device photovoltaic output since the device based on PBTTh~ displayed an effi- ciency of 0.52%, comparable to that of PBTThl.     

Functionalized methanofullerenes used as n-type materials in bulk-heterojunction polymer solar cells and in field-effect transistors

The synthesis of two well-solubilized [60]methanofullerene derivatives ( p- EHO-PCBM and p- EHO-PCBA) is presented for usage in organic solar cells and in field-effect transistors. The para position of the PCBM's phenyl ring was substituted with a branched alkoxy side chain, which contributes to higher solubility, facilitating synthesis, purification, and processing. We find a small change of the open-circuit voltage ( V oc) as a slight improvement in performance upon application in P3HT/[60]methanofullerene bulk-heterojunction-photovoltaic cells, when compared to PCBM, because of the electron donation of the alkoxy group. In the case of the devices with a TiO x layer, the best power conversion efficiencies (PCE, eta e) is observed in a layered structure of P3HT/ p- EHO-PCBA/TiO x (eta e = 2.6%), which slightly exceeds that of P3HT/PCBM/TiO x (eta e = 2.3%) under conditions reported here. This can be attributed, in part, to the carboxylic acid group in p- EHO-PCBA that leads to an effective interface interaction between the active layer and TiO x phase. In addition, n-channel organic field-effect transistor (OFET) devices were fabricated with thin films of p- EHO-PCBM and p- EHO-PCBA, respectively cast from solution on SiO 2/Si substrates. The values of field-effect mobility (mu) for p- EHO-PCBM and p- EHO-PCBA are 1 x 10 (-2) and 1.6 x 10 (-3) cm (2)/V.s, respectively. The results in this paper demonstrate the effects of a carboxylic acid group and an electron-donating substituent in [60]methanofullerenes as n-type materials with respect to organic solar cells and OFET applications.     

Improved Photovoltaic Performance of MEH-PPV/PCBM Solar Cells via Incorporation of Si Nanocrystals

We have studied the effect of silicon nanocrystals （SiNCs） as a third component on performance of organic bulk heterojunction solar cells composed of poly[2-methoxy,5-（2＇-ethylhexyloxy）-l,4-phenylene vinylene] （MEH- PPV）：[6,6]-phenyI-C61-butyric acid methyl ester （PCBM） blend film. By adding suitable amounts of SiNCs into MEH-PPV：PCBM blend, the device performance such as external quantum efficiency, short circuit current density （Js（）, and power conversion efficiency （PCE） improved. Incorporation of 2.5% SiNCs in the blend led to 13.6% improvement of Jsc, which in turn resulted in 18% improvement of PCE up to 2.28%. The improved performance was mainly due to the improvements both in the charge generation from the interface of MEH-PPV/SiNCs and the charge collection at the cathode.     

Efficient Polymer Solar Cells Based on Solution-processed Vanadium Oxide as Hole-extracting Layer

Here we reported the fabrication of efficient polymer solar cells from regioregular poly（3-hexylthiophene） （P3HT）：fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester （PC6jBM） mixtures, in which solution- processed vanadium oxide （VOx） was used as a hole-extracting layer （HEL）. The obtained devices exhibited a high power conversion efficiency of 3.96%, and can be enhanced to 4.06% and 4.16%, respectively, when two types of PEDOT：PSS with different conductivities were used in conjunction with the VOx layer. All the VOx-based devices showed a high fill factor （FF） over 70%, which was ascribed to efficient hole extracting efficiency associated with the solution-processed VOx hole-extracting layer. The origins of the improvement were also studied by transmission spectra, atomic force microscope （AFM）, and capacitance-voltage characteristics.     

New Core-Expanded Naphthalene Diimides for n-Channel Organic Thin Film Transistors

Four classes of core-expanded naphthalene diimides （la, lb, 2a, 2b, 3 and 4） that bear different elec- tron-deficient sulfur heterocycles were designed and synthesized. The solution-processed thin films of la, 2a, 3 and 4 operated well in air as n-channel organic transistors with electron mobility ranging from MO 6 to 0.14 cm2/Vs, depending on the different conjugated backbones. The thin film microstructure studies were also carried out to un- derstand the variations of the electron mobility for thin films of la, 2a, 3 and 4.     

Syntheses and Crystal Structures of Two New Metal Phosphonates： [Mn（H2O）2（C12H8N2） （HO3PCH2CH2CO2） ] and [Co（H2O）4（C10H8N2）]-（HOaPCH2CH2CO2）

By the reactions of manganese（if） acetate, 2-sulfoethylphosphonic acid, 1,10-phen （1,10-phen = 1, 10-phenanthroline） or cobalt（Ⅱ） acetate, 4,4＇-bipy and 2-carboxyethylphosphonic acid, two novel compounds of [Mn（H2O）2（C12H8N2） （HO3PCH2CH2CO2） ] （1） and[Co（H2O）4（C10H8N2）]-（HOaPCH2CH2CO2） （2） have been synthesized and characterized by IR spectroscopy, elemental analyses and single-crystal X-ray diffraction. Compound 1 has a 0D structure. Two Mn（ii） ions are linked by two 2-carboxyethylphosphonic acid ligands, forming a centrosymmetric dimer. These dimers are further interlinked into a 2D layer structure by π-π stacking interactions and hydrogen bonds. Compound 2 has a 1D chain structure. The 2-carboxyethylphosphonic acid remains uncoordinated and acts as the organic template. By the bridge of 4,4＇-bipy, the [Co（4,4＇-bipy）]^2＋ chains are formed.     

Alkyl-functionalized organic dyes for efficient molecular photovoltaics

We designed and synthesized new alkyl-functionalized organic dyes, MK-1 and MK-2, for dye-sensitized solar cells (DSSCs). Based on the MK-2 dye, a high performance of efficiency (eta, 7.7%; short-circuit current density Jsc = 14.0 mA cm-2, open-circuit voltage Voc = 0.74 V, and fill factor FF = 0.74) was achieved under AM 1.5 G irradiation (100 mW cm-2). Remarkably, the relatively higher Voc for DSSCs based on MK-1 and MK-2 dyes, which have long alkyl chains, were observed among the organic dyes caused by the increasing of the electron lifetime in the conduction band of TiO2. Our molecular design of alkyl-functionalized dyes strongly suggests the promising performance of molecular photovoltaics based on organic dyes.     

Fabrication and Characteristics of ZnO/OAD-InN/PbPc Hybrid Solar Cells Prepared by Oblique-Angle Deposition

In this work, lead phthalocyanine (PbPc) and ZnO/InN inorganic semiconductor films prepared by oblique-angle deposition (OAD) were layered to form heterojunction organic/inorganic hybrid photovoltaic solar cells. Among the available organic materials, phthalocyanines, particularly the non-planar ones such as PbPc, are notable for their absorption in the visible and near infrared regions. The organic/inorganic hybrid solar cells fabricated on ZnO/OAD-InN/PbPc showed short-circuit current density (J_SC), open-circuit voltage (V_OC), and power conversion efficiencies (η) of 1.2 mA/cm², 0.6 V and 0.144%, respectively.     

Thieno[3,4-c]pyrrole-4,6-dione based copolymers for high performance organic solar cells and organic field effect transistors

Donor-acceptor type copolymers have wide applications in organic field-effect transistors and organic photovoltaic devices. Thieno[3,4-c]pyrrole-4,6-dione (TPD), as an electron-withdrawing unit, has been widely used in D-A type copolymers recently. Till now, the highest power conversion efficiency and mobility of TPD-based copolymers are over 8% and 1.0 cm² V^-1 s^-1 respectively. In this review, the recent progress of TPD-based copolymers in organic solar cells and organic transistors is summarized.     

Thickness Uniformity Adjustment of Inkjet Printed Light-emitting Polymer Films by Solvent Mixture

In this paper, thickness uniformity of poly（9,9-di-n-octylfluorene） films patterned by inkjet printing was im- proved by the use of solvent mixtures （a solvent with higher volatility, higher surface energy and lower viscosity, with another solvent with lower volatility, lower surface energy and higher viscosity）. The average thickness of inkjet printed poly（9,9-di-n-octylfluorene） films was increased from ca. 30 nm to ca. 100 nm when solvent mixtures were used instead of pure chlorobenzene. More flat PFO films were formed instead of the original films with con- cave-lens like cross-section formed by coffee ring effect. This improvement was explained by combination of in- tense Marangoni flow at early drying process and weak complementary flow at the later drying process formed in the solvent mixture. Patterned poly（9,9-di-n-octylfluorene） films were used for fabrication of electroluminescence devices with improved electronic property. Array of pixels with about 80% effective light-emitting area was ob- tained.     

Hydrogen Adsorption Study upon Ni/AI203 Nano-composite Synthesized by MOCVD Technique

The hydrogen adsorption （storage） studies upon Ni/A1203 nano-composite prepared by metal organic chemical vapor deposition technique （MOCVD） exploiting single source molec ular precursor （SSP） approach were carried out. The Ni/A1203 nano-composite is prepared in cold walled MOCVD reactor by the decomposition of SSP, [H2AI（OtBu）]2, on a substrate holding Ni（acac）2 powder. The SSP is a reducing agent which reduces Ni＋2 to Ni0 and works as source for Al203 matrix in which the Ni0 is dispersed. The resulting Ni/A1203 nano-composite is characterized by XRD, SEM, TEM, and EDX. The hydrogen adsorption （storage） studies are performed using home-made Sievert＇s type apparatus. The hydrogen storage studies reveal that approximately 2.9% （mass ratio） hydrogen can be stored in the Ni/A1203 nano-composite. The results show that Ni/A1203 nano-composite can be a po- tential candidate for hydrogen storage which can be used for onboard fuel purposes.     

Photovoltaic properties of Au/beta-carotene/n-Si organic solar cells

Photovoltaic properties of Au/beta-carotene/n-Si organic solar cells characterized by current-voltage and capacitance-voltage measurements have been investigated. The photocurrent in the reverse direction increases with increasing illumination intensity. The I(sc) increases linearly with light intensity. The I(sc) dependence of light intensity follows a power law I(sc) approximately F(alpha). The exponent alpha was found to be 1.38. This indicates a monomolecular recombination in this device. Au/beta-carotene/n-Si organic solar cells give an open-circuit voltage of 0.316 V and a short-circuit current of 2.33 x 10(-4) A at light intensity of 6 W/m(2). The best conversion efficiency for Au/beta-carotene/n-Si solar cells was found to be 23.3% at a light intensity of 6 W/m(2).     

Application of 4,4＇-（2-Carboxypropane-1,3-diyl）dibenzoic Acid in Coordination Metal Complexes： Synthesis,Characterization, and Theoretical Studies①

[Pb(HL)(phen)]n(1) and [Cd3L2(phen)]n(2), where phen = 1,10-phenanthroline and L = 4,4'-(2-carboxylatopropane-1,3-diyl)dibenzoate, were hydrothermally prepared and fully characterized by X-ray single-crystal diffraction, infrared spectroscopy and thermogravimetric analyses. The decomposition temperature of 1 and 2 was measured to be ca. 304 and 416 ℃, respectively. The charge transfer transition based absorption of 1 and 2 was also verified by the powder scattering spectra and theoretical analyses.     

Molecular engineering of organic sensitizers for dye-sensitized solar cell applications

Novel unsymmetrical organic sensitizers comprising donor, electron-conducting, and anchoring groups were engineered at a molecular level and synthesized for sensitization of mesoscopic titanium dioxide injection solar cells. The unsymmetrical organic sensitizers 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D5), 3-(5-bis(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D7), 5-(4-(bis(4-methoxyphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D9), and 3-(5-bis(4,4'-dimethoxydiphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D11) anchored onto TiO2 and were tested in dye-sensitized solar cell with a volatile electrolyte. The monochromatic incident photon-to-current conversion efficiency of these sensitizers is above 80%, and D11-sensitized solar cells yield a short-circuit photocurrent density of 13.90 +/- 0.2 mA/cm(2), an open-circuit voltage of 740 +/- 10 mV, and a fill factor of 0.70 +/- 0.02, corresponding to an overall conversion efficiency of 7.20% under standard AM 1.5 sun light. Detailed investigations of these sensitizers reveal that the long electron lifetime is responsible for differences in observed open-circuit potential of the cell. As an alternative to liquid electrolyte cells, a solid-state organic hole transporter is used in combination with the D9 sensitizer, which exhibited an efficiency of 3.25%. Density functional theory/time-dependent density functional theory calculations have been employed to gain insight into the electronic structure and excited states of the investigated species.     

双链结构有机光敏染料的合成及性能

设计合成了2个含双D-π-A结构的新型有机光敏染料DP1和DP2,利用高分辨质谱(HRMS)、核磁共振氢谱及核磁共振碳谱对其结构进行了表征。 研究了2个染料的光物理和电化学性质,并将其应用于染料敏化太阳能电池(DSSCs)的制作中。 在100×10-3 W/cm2(AM 1.5) 模拟太阳光的照射下,由染料DP2所制备的敏化太阳能电池的光电转化效率为4.10%;开路电压(Voc)、短路电流密度(Jsc)和填充因子(FF)分别为0.63 V、8.59×10-3 A/cm2和0.76。 而在同等条件下,由染料DP1所制作的染料敏化电池光电转化效率为3.83%。     

Recent structural evolution of lactam- and imide-functionalized polymers applied in organic field-effect transistors and organic solar cells

Organic semiconductor materials, especially donor–acceptor (D–A) polymers, have been increasingly applied in organic optoelectronic devices, such as organic field-effect transistors (OFETs) and organic solar cells (OSCs). Plenty of high-performance OFETs and OSCs have been achieved based on varieties of structurally modified D–A polymers. As the basic building block of D–A polymers, acceptor moieties have drawn much attention. Among the numerous types, lactam- and imide-functionalized electron-deficient building blocks have been widely investigated. In this review, the structural evolution of lactam- or imide-containing acceptors (for instance, diketopyrrolopyrrole, isoindigo, naphthalene diimide, and perylene diimide) is covered and their representative polymers applied in OFETs and OSCs are also discussed, with a focus on the effect of varied structurally modified acceptor moieties on the physicochemical and photoelectrical properties of polymers. Additionally, this review discusses the current issues that need to be settled down and the further development of new types of acceptors. It is hoped that this review could help design new electron-deficient building blocks, find a more valid method to modify already reported acceptor units, and achieve high-performance semiconductor materials eventually.

This review highlights the recent structural evolution of lactam- and imide-functionalized polymers applied in organic field-effect transistors and organic solar cells.     

Efficient eosin y dye-sensitized solar cell containing Br-/Br3- electrolyte

We found that Br-/Br3- is more suitable than an I-/I3- couple in dye-sensitized solar cells in terms of higher open-circuit photovoltage (Voc) production and higher overall energy conversion efficiency (eta) if the dye sensitizer has a more positive potential than that of Br-/Br3-. Under simulated AM1.5 one sun, an eosin Y dye-sensitized solar cell containing 0.4 M LiBr + 0.04 M Br2 electrolyte in acetonitrile yielded a short-circuit photocurrent (Jsc) of 4.63 mA cm(-2), Voc of 0.813 V, and fill factor (FF) of 0.693, corresponding to 2.61% of eta. Under the same conditions except for the electrolyte 0.4 M LiI + 0.04 M I2 in acetonitrile instead, the device produced 1.67% of eta (Jsc = 5.15 mA cm(-2), Voc = 0.451 V, FF = 0.721). Replacement of I-/I3- with Br-/Br3- in eosin Y dye-sensitized solar cells yielded a significant increase in Voc offset by slight decreases in Jsc and FF, leading to an increase in eta by 56%. The significant gain in Voc was attributed to the enlarged energy level difference between the redox potential of the electrolyte and the Fermi level of TiO2 and the suppressed charge recombination as well. The rate for charge recombination between bromine and the injected electrons was determined to be first order in bromine.     

Organic Fluorescent Molecule with High Solid State Lumines- cent Efficiency and Protonation Stimuli-response

A novel organic fluorophor with high solid state luminescent efficiency based on 1,4-bis（2,2-di（pyridin-2-yl）- vinyl）benzene （BDP2VB） was designed and synthesized. It emits faintly in solution, but becomes a strong emitter in the aggregate state, demonstrating its aggregation induced emission （AIE） property. According to the crystal struc- ture analysis, J-type aggregation was formed in the packing mode of the molecule, which was demonstrated to be beneficial to gain high fluorescent quantum efficiency in solid state. Additionally, the emission color of BDP2VB can change dramatically in solid state as well as in solution by the protonation stimuli.     

Determination of quasi-Fermi levels across illuminated organic donor/acceptor heterojunctions by Kelvin probe force microscopy

Using Kelvin probe force microscopy (KFM), we have measured the electrochemical potentials across indium tin oxide/organic and donor/acceptor heterojunctions in the dark and under illumination with white light. We have found that the photovoltage generated across these heterojunctions is strongly correlated with the difference between the respective HOMO and LUMO levels of the donor and acceptor and also very closely approximates measured open-circuit voltages in completed solar cells. These results imply that KFM tracks the Fermi level positions within the donor and acceptor layers under photoexcitation. Overall, these results demonstrate the utility of KFM for understanding potential profiles across active layers in planar-heterojunction organic solar cells.