4.7- Di-2-thienyl-2,l,3-benzothiadiazole

After that, Cao and coworkers synthesized a series of copolymers derived from DOF and narrow-band-gap 4,7-di-2-thienyl-2,l,3-benzothiadiazole (DBT) with various feed ratios of DOF/DBT [58]. The highest quantum efficiency and brightness were only 1.4% and 259 cdm2, respectively, from the device based on the copolymer with 15% DBT content (ITO/PEDOT PSS/27/Ba/Al). As DBT content increases from 1 to 35%, the EL emission peak shifts from 628 nm to 674 nm, indicating that the copolymers are promising candidates as pure-red emitters though the performance needs to be further improved. 

Andersson and coworkers have prepared solar cells based on blends of poly(2,7-(9-(2 -ethylhexyl)-9-hexyl-fluorene)-fl/t-5,5-(4, 7 -di-2-thienyl-2, l, 3 -benzothiadiazole) (223) and PCBM [416]. The polymer shows a Amax (545 nm) with a broad optical absorption in the visible spectrum and an efficiency of 2.2% has been measured under simulated solar light. The same group has also reported the synthesis of low bandgap polymers 200 (1 = 1.25 eV) and 224 (1 = 1.46 eV) which have been blended with a soluble pyrazolino[70]fiillerene and PCBM, respectively, to form bulk heterojunction solar cells of PCE of 0.7% [417] and 0.9% [418]. Incorporation of an electron-delident silole moiety in a polyfluorene chain affords an alternating conjugated copolymer (225) with an optical bandgap of 2.08 eV. A solar cell based on a mixture 1 4 of 225 and PCBM exhibits 2.01% of PCE [419]. 

Scheme 59 Structural formulas of selected commercially available donors poly (3-hexylthiophene-2,5-diyl), (P3HT) and poly[Af-9 -heptadecanyl-2,7-carbazole-alt-5,5-(4, 7 -di-2-thienyl-2, r,3 -benzothiadiazole)], (PCDTBT), and acceptor molecules for BHJ SCs l, r, 4, 4"-tetrahydro-di [1,4] methanonaphthaleno[l,2 2, 3, 56,60 2",3"] [5,6] fullerene-CgO) (ICBA) and [6, 6] -phenyl-Cvi butyric acid methyl ester, (PC71BM), used in Ref. [108]...

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