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Abstract: Poly [3,3‴-didodecylquaterselenophene] (PQS) and poly[3,3‴-didodecylquaterselenophene-alt-didodecylquaterthiophene] (PQSQT), have been synthesized by using a Stille cross-coupling reaction. The weight-averaged molecular weights (M w ) of PQS and PQSQT were found to be 18,900Da and 22,300Da with polydispersity indices of 1.71 and 1.99, respectively. Photophysical measurements found the low bandgaps of 1.73eV for PQS and 1.86eV for PQSQT. The field-effect mobilities of PQS and PQSQT were determined to be 6.0×10−3 and 0.05cm2/Vs, respectively. The influence of the selenium and sulfur atoms in the polymer backbones were investigated with regard to device performances. The polymers were combined with the PC71BM ([6,6]-phenyl C71-butyric acid methyl ester) acceptor to fabricate bulk heterojunction solar cells with power conversion efficiencies of 0.73–2.37% under AM 1.5G (100mW/cm2) conditions. [Copyright &y& Elsevier]

Abstract: A new conjugated polymer containing pentaselenophene (5Se) electron donor moieties was designed for use in polymer solar cells and synthesized via a Stille coupling reaction. The structure, optical properties, electrochemical properties, hole mobility, photovoltaic properties, and AFM morphology of the homopolymer (P5Se) and the donor–acceptor copolymer (P5SeDTDPP) with a diketopyrrolopyrrole (DPP) acceptor were investigated and are discussed. The polymers showed good solubility, film-forming properties, and thermal stabilities. P5Se exhibited a broad absorption across the visible range, 400–700nm, which is a prerequisite for photovoltaic applications. P5SeDTDPP yielded a broader absorption spectrum, enhanced π–π interactions, and a lower band gap compared to P5Se, due to the enhanced intramolecular charge transfer interactions between the donating moiety (pentaselenophene) and the DPP accepting moiety. Solution-processed field effect transistors fabricated from these polymers displayed p-type organic thin film transistor characteristics. P5Se and P5SeDTDPP exhibited typical p-type organic semiconductor characteristics with hole mobilities of 2.3×10−3 and 1.2×10–2 cm2 V−1 s−1, respectively. Photovoltaic devices were fabricated using polymer:PCBM blends in ITO/PEDOT:PSS/blend/Al structures. The P5SeDTDPP device exhibited an open circuit voltage (V OC) of 0.44V, a short circuit current (J SC) of 10.67mA/cm2, a fill factor (FF) of 0.51, and a power conversion efficiency (PCE) of 2.40% under AM 1.5G (100mW/cm2) conditions. [Copyright &y& Elsevier]

Abstract: Arylenevinylene based bis(arylhalide) monomers were synthesized as low band gap electron-accepting blocks, and were copolymerized with 9,9-dioctyl-2,7-fluorene or 9-(heptadecan-9′-yl)-2,7-carbazole diboronic esters as electron-donating blocks using Suzuki coupling polymerization. Four alternating copolymers were synthesized through the combination of two different bis(arylhalide)s and diboronic esters, and their optical, thermal and electrochemical properties were characterized. The intra-molecular charge transfer interaction between the electron donating and electron accepting blocks in the polymeric backbone induced a broad absorption from 300 to 650nm. The optical band gap energies of the polymers were measured from their absorption onsets to be 1.97–2.18eV depending on the polymer structure. Bulk heterojunction photovoltaic devices were fabricated using the synthesized polymers as the electron donors and 6,6-phenyl C71-butyric acid methyl ester (PC70BM) as the electron acceptor. One of these devices showed a high power conversion efficiency of 3.22%, with an open-circuit voltage of 0.74V, a short-circuit current of 10.60mA/cm2, and a fill factor of 0.41 under air mass (AM) 1.5 global (1.5G) illumination conditions (100mW/cm2). [Copyright &y& Elsevier]

Abstract: We synthesized oleic acid capped tetrapod nanocrystals of CdSe, CdTe and type II heterostructured CdTe/CdSe to investigate the effects of nanocrystal compositions and type II heterojunction on the photovoltaic properties of hybrid solar cells. The hybrid solar cell based on the blend of CdSe tetrapod nanocrystals and P3HT with a weight ratio of 6:1 showed the maximum power conversion efficiency of 1.03% under AM 1.5G condition, and the maximum incident photon to current conversion efficiency of the solar cell was 43% at 415nm. Although CdTe and CdTe/CdSe tetrapod nanocrystals showed relatively poor performance, the power conversion efficiency and the short circuit current density of the hybrid solar cell based on type II heterostructured CdTe/CdSe tetrapod nanocrystals was 4.4 and 3.9 times higher than that of the solar cell based on CdTe tetrapod nanocrystals, respectively. These results can be explained by the effects of nanocrystal compositions and type II heterojunction on the photovoltaic properties of hybrid solar cells. [ABSTRACT FROM AUTHOR]

A series of donor-rich semi-random copolymers with various benzodithiophene (donor unit)/fluorinated-thienothiophene (acceptor unit) ratios – D2A, D3A, D5A, D7A – were designed and synthesized for use in polymer solar cells (PSCs). The polymer D1A was also synthesized for comparison. The optical and electrochemical properties of these polymers vary with the number of donor units in their polymer backbones. The device containing the polymer D5A exhibits a best power conversion efficiency (PCE) of 5.52% when the active layer thickness is 340 nm, a value that is 80% of its maximum PCE, whereas the best PCE of the D1A-based device is reduced by 32% when the active layer thickness is 310 nm. A large area (6,270 mm 2 ) D5A-based device prepared with the slot die-coating method was found to exhibit a best PCE of 6.54%, which is significantly better than that of the equivalent D1A-based large area device (4.03%). [ABSTRACT FROM AUTHOR]

Abstract: 2,2′,7,7′-Tetra(9,9-diethyl-9H-fluorene)-9,9′-bifluorenylidene (TFBF) was synthesized as a non-fullerene type electron acceptor for bulk-heterojunction polymer solar cells. The TFBF was synthesized from 2,7-di(9,9-diethyl-9H-fluorene)-9H-fluoren-9-one by a reductive dimerization using Lawesson's reagent. The TFBF was soluble in common organic solvents such as dichloromethane, chloroform, and 1,2-dichlorobenzene. The synthesis of TFBF was identified by 1H NMR, 13C NMR, FAB-Mass, and FT-IR, and the properties of the molecule were characterized by UV–visible absorption and fluorescence spectroscopy. The ionization potential of the TFBF solid thin film was determined by photo-electron spectroscopy, and morphology of the active layer was investigated by atomic force microscope. The measured optical band gap, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of TFBF were 2.32, −5.81, and −3.49eV, respectively. Photoluminescence (PL) spectra of P3HT solution in chloroform were measured at different TFBF concentration. The PL intensity of P3HT solution was decreased by increasing the TFBF concentration. The electron mobility of P3HT:TFBF blend film was measured to be 6.82×10−5 cm2/Vs at the electric field of 500 (V/cm)1/2. Photovoltaic devices were fabricated with the structure of ITO/PEDOT:PSS/P3HT:TFBF/LiF/Al. One of the fabricated device showed the highest V oc of 0.70V with J sc =1.20mA/cm2, FF=0.30, and PCE=0.26% at donor to acceptor composition ratio of 1:0.4. [Copyright &y& Elsevier]

Abstract: A new series of fullerene (C60) multiadducts of methyl ester substituted thieno-o-quinodimethane were synthesized for polymer solar cells (PSCs). The synthesized 5-methyl ester thieno-o-quinodimethane fullerene (C60) multiple adducts, such as METFMA (mono-adduct), METFBA (bis-adduct) and METFTA (tris-adduct), showed good solubility in toluene, CHCl3 and ODCB. Their molecular structures were confirmed by 1H, 13C NMR, UV–visible spectroscopy, DSC, TGA and HRMS Cyclic voltammetry revealing a lowest unoccupied molecular orbital (LUMO) energy level of −3.65eV for METFMA, −3.53eV for METFBA and −3.42eV for METFTA, which is higher than that of PC61BM. The higher LUMO energy level of METFMA, METFBA and METFTA resulted in an enhancement of the open-circuit voltages (V oc) of PSCs. Device of the multiple adduct acceptors was blended with a P3HT donor with the configuration, ITO/PEDOT/P3HT:acceptor/LiF/Al, using METFMA, METFBA, METFTA and PC61BM as the electron acceptor. The optimal photovoltaic performances were achieved using METFBA and METFTA with power conversion efficiencies of 3.00% and 2.93%, respectively. These results were comparable to the device conducted with P3HT:PC61BM (3.42%) under the same conditions. [Copyright &y& Elsevier]

Abstract: A new donor unit viz. 3,8-bis(2-butyloctyloxy)naphtho[3,2-b:7,6-b′]dithiophene (NDT) was developed for a novel donor–acceptor semiconducting polymer. And the new NDT-based polymers (PNDTTT-C and PNDTTT-CF) with thienothiophene units were synthesized. The polymers showed deep HOMO levels of −5.44eV and −5.51eV with the optical band gap of ∼1.6eV. The electrochemical as well as optical and photovoltaic properties of these polymers were studied. The OPV devices fabricated from the blends of polymer PNDTTT-C/PNDTTT-CF: PC71BM were afforded a high power conversion efficiency of 4.49% and 5.16%, respectively. The optimization of device fabrication included different solvents, different weight ratios and usage of solvent processing additive. To obtain the high PCE a typical processing additive 1,8-diiodooctane was used. The effect of processing additive was studied using AFM analysis. In addition, the field-effect hole mobilities of 3.5×10−4 cm2V−1s−1 and 5.7×10−4 cm2V−1s−1 were observed for the polymers PNDTTT-C and PNDTTT-CF, respectively. Since we have developed the synthetic process of the 3,8-bis(2-butyloctyloxy)- naphtho[3,2-b:7,6-b′]dithiophene(NDT) monomer, the NDT unit will play an important role in future research on conjugated polymer and small molecule design for high-performance organic semiconducting material. [Copyright &y& Elsevier]

Abstract: A series of low band gap polymers composed of benzotriazole and benzo[1,2-b:4,5-b′]dithiophene derivatives were synthesized using a Stille cross-coupling reaction for use in organic photovoltaic devices. Linear or branched alkyl groups were incorporated into the benzothiazole-based accepting monomer part, and alkoxy or alkylthiophene groups were introduced to benzo[1,2-b:4,5-b′]dithiophene-based donating monomer part. Changes in photo-physical properties of the polymers by the structural modification of the donor–acceptor type low band gap polymers were investigated. The synthesized polymers were soluble in common organic solvents, and the resulting polymer solutions could be used to form smooth and uniform thin films by spin-casting. The synthesized polymers were found to exhibit good thermal stability, losing less than 5% of their weight upon heating to approximately 300°C. The intra-molecular charge transfer interaction between the electron donating and electron accepting blocks in the polymeric backbone induced a broad absorption from 300 to 650nm. The optical band gap energies of the polymers were measured to be 2.03–1.90eV depending on the polymer structure. Solution-processed field-effect transistors were fabricated and characterized using the polymers as p-type channel materials. Bulk hetero-junction photovoltaic devices were fabricated using the polymers with [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) as the electron acceptor. One of the fabricated device showed the maximum power conversion efficiency of 3.20% under AM 1.5G (100mW/cm2) conditions. [Copyright &y& Elsevier]

Abstract: New thermally robust photoactive arylenevinylene-based conjugated polymers, poly[3,6-bis(3,7-dimethyloctyloxy)-9,9-spirobifluorenyl-2,7-vinylene] [(OC10)2-spiro-PFV] and poly[{3,6-bis(3,7-dimethyloctyloxy)-9,9-spirobifluorenyl-2,7-vinylene}-co-2-{methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene}] [(OC10)2-spiro-PFV-co-MEH-PPV], were synthesized and used to fabricate polymer solar cells. Bulk heterojunction solar cells fabricated by blending the new copolymers, spiro-PFV and (OC10)2-spiro-PFV-co-MEH-PPV, as an electron donor with the fullerene derivative, [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as an electron acceptor. The effects of electron donor to acceptor ratio, thickness of photoactive layer, and the cathode structures on the power conversion efficiency (PCE) in polymer solar cells were studied. The copolymer feed ratio was found to have a considerable effect on the PCE. The maximum PCE of 1.30% was achieved with (OC10)2-spiro-PFV-co-MEH-PPV. [Copyright &y& Elsevier]