Conjugated Copolymers Based on Fluorene−Thieno[3,2-b]thiophene for Light-Emitting Diodes and Photovoltaic Cells

Citations Over TimeTop 1% of 2007 papers

Abstract

Alternating conjugated copolymers comprised of 9,9-dihexylfluorene and unsubstituted/substituted thieno[3,2-b]thiophene moieties were synthesized using the Suzuki coupling reaction. The structures of these polymers were characterized, and their thermal, photophysical, electrochemical, and electroluminescent properties were investigated. By β-substitution of thieno[3,2-b]thiophene moiety with alkyl chain, the thermal, electrochemical, and electroluminescence properties of the resulted polymers were tuned. The polymers exhibited good thermal stability with decomposition temperature (Td) in the region of 308−431 °C and their glass transition temperatures (Tg) ranging from 126 to 146 °C. Incorporation of β-alkyl chain onto thieno[3,2-b]thiophene of the alternating copolymers led to lowered Tdand Tg and blue-shifted maximum wavelengths in both absorption and emission spectra. The influence of β-alkyl substitution on the conformation of the polymer chains was evaluated by simulating the optimized geometries of three model oligomers using density functional theory. Light-emitting diode devices were fabricated with a configuration of ITO/PEDOT:PSS/polymer/Ca/Ag for all the polymers. A device based on fluorene and unsubstituted thieno[3,2-b]thiophene polymer (P2) exhibited pure green emission with a maximum brightness of 6000 cd/m2 and current efficiency of 2.7 cd/A. More importantly, this device demonstrated very good spectral stability and robust emission, with only 21% decay in luminance after 64 h driving at 1 mA of constant current. In addition, the potential application of the copolymers for photovoltaic solar cells was discussed.

Related Papers

• → Conjugated polymers containing electron‐transporting, hole‐transporting, and light‐emitting units in the polymer main chain(2007)28 cited
• → π-Conjugated poly(anthracene-alt-fluorene)s with X-shaped repeating units: New blue-light emitting polymers(2008)18 cited
• → Aliphatic‐aromatic copolycarbonates derived from 2,2,4,4‐tetramethyl‐1,3‐cyclobutanediol(1995)10 cited
• Pi-Conjugated poly(anthracene-alt-fluorene)s with X-shaped repeating units: New blue-light emitting polymers(2008)
• → Blue Electroluminescent Copolymers Containing Fluorene and Flexible Segments(2006)