Issue 28, 2014

Efficient deep blue fluorescent polymer light-emitting diodes (PLEDs)


A new series of deep blue/blue emitting co-polymers are reported. Poly(9,9-dihexylfluorene-3,6-diyl and 2,7-diyl-co-2,8-dihexyldibenzothiophene-S,S-dioxide-3,7-diyl) derivatives p(F-S) of varying composition have been synthesised. The effects of two different S derivatives with dialkoxy sidechains, the F : S monomer feed ratio, and meta versus para conjugation with respect to the F units have all been investigated in terms of photophysics and polymer light-emitting diode (PLED) device performance in the architecture ITO/PEDOT:PSS/polymer/TPBi/LiF/Al. The meta polymers poly(9,9-dihexylfluorene-3,6-diyl-co-2,8-di(O-methylenecyclohexyl)dibenzothiophene-S,S-dioxide-3,7-diyl) p(Fm-SOCy) in three different co-monomer ratios, P1–3, give deep blue electroluminescence peaking at 415 nm, with the ratio of 70 : 30 p(Fm : SOCy) producing a maximum external quantum efficiency (EQE) ηext, max 2.7%, whilst the ratio of 85 : 15 gave the highest maximum brightness Lmax of 81 cd m−2, with CIE coordinates (0.17, 0.12) The analogous para series poly(9,9-dihexylfluorene-2,7-diyl-co-2,8-di(O-methylenecyclohexyl)dibenzothiophene-S,S-dioxide-3,7-diyl) p(Fp-SOCy) and poly(9,9-dihexylfluorene-2,7-diyl-co-2,8-dihexyloxydibenzothiophene-S,S-dioxide-3,7-diyl) p(Fp-SO6) in two different ratios, P4–7, produced blue emission peaking at ca. 450 nm. The ratio of 70 : 30 F : S units consistently gave better devices than the corresponding 50 : 50 co-polymers. It was also observed that co-polymers incorporating the bulkier SOCy derivatives gave more efficient and brighter devices, with polymer P5 attaining a remarkable ηext, max 3.2%, 4.4 cd A−1, 3.4 lm W−1 and maximum brightness 2500 cd m−2 with CIE (0.16, 0.18).

Graphical abstract: Efficient deep blue fluorescent polymer light-emitting diodes (PLEDs)

Supplementary files

Article information

Article type
01 May 2014
25 May 2014
First published
12 Jun 2014
This article is Open Access
Creative Commons BY license

J. Mater. Chem. C, 2014,2, 5587-5592

Efficient deep blue fluorescent polymer light-emitting diodes (PLEDs)

J. H. Cook, J. Santos, H. Li, H. A. Al-Attar, M. R. Bryce and A. P. Monkman, J. Mater. Chem. C, 2014, 2, 5587 DOI: 10.1039/C4TC00896K

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