PTB7-Th-b-PNDI fully conjugated donor-acceptor block copolymers for thermal stability of photovoltaic devices

In recent, the long-term stability of organic solar cells, including both photo-stability and thermal stability, has received growing attention. As the sole active layer material and phase compatibilizer in blend systems, photovoltaic devices including fully conjugated donor-acceptor block copolymers are expected to display enhanced thermal stability than the corresponding blend systems. We prepared Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)]-block-Poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (PTB7-Th-b-PNDI) donor-acceptor block copolymer using a Stille reaction twice. Formation of block copolymers was confirmed by NMR and GPC. Solar cell devices were fabricated using the donor-acceptor block copolymer as the sole active layer material as well as with the block copolymer as an additive in PTB7-Th/PNDI and PTB7-Th/PCBM blend systems. Upon thermal stress at 80 ^oC for up to 168 hours, blend solar cells with addition of block copolymers exhibited enhanced thermal stability. Morphology of blends with or without addition of the block copolymer was investigated by RSoXS and EF-TEM.