Yingping Zou

Copolymers from benzodithiophene and benzotriazole: synthesis and photovoltaic applications

Two new alternating low bandgap copolymers from benzodithiophene and benzotriazole units, namely poly{4,8-bis(2-ethylhexyloxy)benzo[1,2-b; 3,4-b]dithiophene-2,6-diyl-alt-2-octyl-4,7-di(thiophen-2-yl)-2H-benzo[d][1,2,3]triazole-5′,5′′-diyl} (PBDTDTBTz) and poly{4,8-bis(2-ethylhexyloxy)benzo[1,2-b;3,4-b]dithiophene-2,6-diyl-alt-2-dodecylbenzotriazole-4,7-diyl} (PBDTBTz), were designed and synthesized by a typical Stille coupling polymerization method. The copolymers were characterized by thermogravimetric analysis, UV-vis absorption and cyclic voltammetry. PBDTDTBTz and PBDTBTz possess moderate molecular weights and excellent thermal properties with a 5% weight loss temperatures (Td) around 300 °C. They exhibited good optical absorption, with peaks at 527 nm and 562 nm in the film state, respectively. Photovoltaic properties of the copolymers blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) or [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as electron acceptors, were investigated. The photovoltaic device with the PBDTDTBTz/PC71BM shows a power conversion efficiency of 1.7% with a short circuit current density of 4.5 mA cm−2 and a good fill factor of 0.62, while PBDTBTz demonstrated a moderate power conversion efficiency of up to 1.4%, under the illumination of AM 1.5, 100 mW cm−2 with a device structure of ITO/PEDOT: PSS/polymer: PC71BM (1u2006:u20064)/Ca/Al. All the above information highlighted that this kind of the copolymers is promising for the application of polymer solar cells.

New low bandgap dithienylbenzothiadiazole vinylene based copolymers: synthesis and photovoltaic properties.

Two new low-bandgap block copolymers derived from dithienylbenzothiadiazole (DTBT) and different electron-rich functional groups (dioctoxyl benzene and N-octyl-diphenylamine), poly(1,4-dioctoxyl-2,5-divinylbenzene-co-4,7-dithiophene-2-yl-2,1,3-benzothiadiazole) (PPV-DTBT), poly(3,8-divinyl-N-octyl-diphenylamine-co-4,7-dithiophene-2-yl-2,1,3-benzothiadiazole) (PDPAV-DTBT), were synthesized by Heck cross-coupling polymerization. PPV-DTBT and PDPAV-DTBT are easily soluble in common organic solvents such as o-dichlorobenzene and chloroform. DSC and TGA results indicate that these copolymers possess good thermal stabilities. PPV-DTBT and PDPAV-DTBT films exhibit broad absorption bands at 300-765u2009nm (with an optical bandgap of 1.62u2009eV) and 300-733u2009nm (with an optical bandgap of 1.69u2009eV), respectively. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of PPV-DTBT were estimated by cyclic voltammetry to be -5.43 and -3.74u2009eV, respectively, and the HOMO and LUMO of PDPAV-DTBT were -5.37 and -3.7u2009eV, respectively. Preliminary photovoltaic cells based on the composite structure of ITO/PEDOT: PSS/PPV-DTBT:PCBM (1: 2, w/w)/Al showed an open-circuit voltage of 0.75u2009V, a power conversion efficiency of 0.6%, and a short circuit current of 1.7u2009mAu2009·u2009cm(-2) .