Synthesis and photovoltaic device studies of azo‐linked low‐bandgap polymers

Abstract

We report the synthesis of a series of new polymers containing azo linkage as a part of the main chain. The monomer 1,2‐bis(7‐bromo‐9,9‐dioctyl‐9H‐fluoren‐2‐yl)diazene was synthesized using a precursor approach which avoids non‐selective bromination and was copolymerized with various donor or acceptor units. The homopolymer poly[1,2‐bis(9,9‐dioctyl‐9H‐fluoren‐2‐yl)diazene] (P1) as well as the copolymers poly[1‐(9,9‐dioctyl‐9H‐fluoren‐2‐yl)‐2‐(9,9,9′,9′‐tetraoctyl‐9H,9′H‐[2,2′‐bifluoren]‐7‐yl)diazene] (P2), poly[1‐(9,9‐dioctyl‐7‐(4‐octylthiophen‐2‐yl)‐9H‐fluoren‐2‐yl)‐2‐(9,9‐dioctyl‐9H‐fluoren‐2‐yl)diazene] (P3) and poly[4‐(7‐((9,9‐dioctyl‐9H‐fluoren‐2‐yl)diazenyl)‐9,9‐dioctyl‐9H‐fluoren‐2‐yl)benzo[c][1,2,5]thiadiazole] (P4) were synthesized by Suzuki polymerization. The copolymers poly[1‐(7‐(4,4‐dioctyl‐4H‐cyclopenta[1,2‐b:5,4‐b′]dithiophen‐2‐yl)‐9,9‐dioctyl‐9H‐fluoren‐2‐yl)‐2‐(9,9‐dioctyl‐9H‐fluoren‐2‐yl)diazene] (P5) and poly[4‐(5‐(7‐((9,9‐dioctyl‐9H‐fluoren‐2‐yl)diazenyl)‐9,9‐dioctyl‐9H‐fluoren‐2‐yl)‐4‐octylthiophen‐2‐yl)‐7‐(4‐octylthiophen‐2‐yl)benzo[c][1,2,5]thiadiazole] (P6) were synthesized by direct arylation polymerization reaction. Polymers synthesized using the direct arylation method show good molecular weight, with absorption maxima in the range 500 to 532 nm. P5 and P6 possess low optical bandgaps of 1.81 and 1.86 eV, respectively. A power conversion efficiency of 0.53% with open circuit voltage of 0.53 V, short circuit current density of 3.1 mA cm−2 and fill factor of 29% has been achieved with C71‐PCBM as acceptor in bulk heterojunction solar cells fabricated with P5 as donor. © 2016 Society of Chemical Industry

Novel Azocoumarin Derivatives—Synthesis and Characterization

“…All of these solar cells have shown similar shunt (R SH ) and series (R S ) resistances, what might be a result of poor film-forming properties of the azo-compounds used in these active layers. The devices revealed similar and very low average power conversion efficiencies being in a range of 0.05–0.10%, which is similar to those obtained for other azo-dyes [ 19 , 20 ] or azo-polymers [ 21 ] reported in literature. The highest PCE was registered for a PV cell with an active layer consisting of compound with methyl substituent ( 6g ) (0.12% max.).…”

Design and synthesis of N-substituted perylene diimide based low band gap polymers for organic solar cell applications

“…† The synthesis of the target monomers 2,9-bis(7-bromo-9,9-dioctyl-9 H -fluoren-2-yl)anthrax[2,1,9-def:6,510-d,e,f′]diisoquinoline-1,3,8,10(2 H ,9 H )tetraone (M1), 2,2′-(9,9-dioctyl-9 H -fluoren-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (M2) and 4,7-bis(4-octylthiophen-2-yl)benzo[ c ]-1,2,5-thiadiazole (M4) were carried out as follows: in the first step bromination followed by alkylation of fluorene 1 in presence of N-bromosuccinimide (NBS) and n -octyl bromide, respectively, yielded 2-bromo-9,9-dioctylfluorene 2 (90%) which on nitration in the second step followed by reduction gave 2-amino-7-bromo-9,9-dioctylfluorene 4 in 74% overall yield. 40 Reaction of 4 with perylene-3,4,9,10-tetracarboxylic dianhydride in the presence of imidazole and anhydrous zinc acetate on heating at 160 °C under N 2 atmosphere resulted in M1 in 90% yield. Bromination of 1 in presence of bromine gave dibromofluorene which on alkylation with n -octyl bromide using tetrabutylammonium hydroxide at 80 °C gave 2,7-dibromo-9,9-dioctyl-9 H -fluorene 5 in 90% yield.…”

“…2-Bromo-9,9-dioctylfluorene (2), 2-bromo-7-nitro-9,9-dioctylfluorene (3), 2-amino-7-bromo-9,9-dioctylfluorene (4), 2,7-dibromo-9,9-dioctyl-9 H -fluorene (5) and 4,4,5,5-tetramethyl-2-(4-octylthiophene-2-yl)-1,3,2-dioxaborolane (6) were synthesized by reported literature procedures. 40–42 2,2′-(9,9-Dioctyl-9 H -fluoren-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (M2) and 4,7-bis(4-octylthiophen-2-yl)benzo[ c ]-1,2,5-thiadiazole (M4) were synthesized by reported methods with modified reaction conditions and improved yields 43,44 (details were given in ESI † ).…”