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Synthesis and characterization of light‐absorbing cyclopentadithiophene‐based donor–acceptor copolymers
Author(s) -
Sharma Bhavna,
Sarothia Yameeni,
Singh Ranbir,
Kan Zhipeng,
Keivanidis Panagiotis E,
Jacob Josemon
Publication year - 2016
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.5024
Subject(s) - stille reaction , polymer chemistry , carbazole , materials science , copolymer , condensation polymer , acceptor , conjugated system , polymerization , monomer , polymer , chemistry , organic chemistry , physics , composite material , condensed matter physics
Cyclopentadithiophene and benzothiadiazole based donor–acceptor polymers are fast emerging as the most promising class of materials for organic solar cells. Here we report on a series of Cyclopentadithiophene and benzothiadiazole based conjugated polymers, namely poly[4,7‐bis(4,4‐dioctyl‐ 4H ‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole] ( P1 ), poly[4,7‐bis(4,4‐dioctyl‐ 4H ‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole‐ alt ‐9‐(heptadecan‐9‐yl)‐2,7‐bis(4,4,5,5‐tetramethyl)‐1,3,2‐dioxaborolan‐2‐yl)‐ 9H ‐carbazole] ( P2 ) and poly[4,7‐bis(4,4‐dioctyl‐ 4H ‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole‐ alt ‐5,11‐bis(2‐hexyldecyl)‐3,9‐bis(4,4,5,5‐tetramethyl)‐1,3,2‐dioxaborolan‐2‐yl)‐5,11‐dihydroindolo[3,2‐b]carbazole] ( P3 ), with alternating donor and acceptor units and discuss their photophysical and electrochemical properties. Stille coupling of 2‐tributylstannyl‐4,4‐dioctylcyclopenta[2,1‐b:3,4‐b′]dithiophene with 4,7‐dibromobenzo[1,2,5]thiadiazole generated the alternating donor–acceptor monomer 4,7‐bis(4,4‐dioctyl‐ 4H ‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole ( CPDT‐BT‐CPDT ). Homopolymer P1 of CPDT‐BT‐CPDT was synthesized by oxidative polymerization using FeCl 3 . Copolymers P2 and P3 were synthesized by palladium‐catalysed Suzuki polycondensation. The synthesized polymers showed good solubility in common organic solvents, and UV ‐visible measurements showed that the absorption maxima of the polymers lie in the range 624 to 670 nm. The energy gaps of these polymers were found to lie in the range 1.29 to 1.50 eV . Gel permeation chromatography measurements against polystyrene standards showed the number‐average molecular weight to be in the range (2.2–6.0) × 10 4 g mol −1 . Thermogravimetric analysis showed the polymers to possess high thermal stability. A preliminary study of photodiode devices prepared using polymers P1 , P2 and P3 when blended with the PC 71 BM electron acceptor found that P2 is the optimum chemical structure for pursuing further device optimization.© 2015 Society of Chemical Industry