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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: 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 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]