We report investigations of the photoluminescence (PL) and electroluminescence (EL) of a thiophene oligomer for which we have devised a variety of substitutions aimed at enhancing the solid-state efficiency. We find that the absolute PL quantum efficiency in the solid state is up 37% for both powders or spin-coated thin films of the compound. The material thus becomes competitive for applications in organic light-emitting diodes (LEDs). EL efficiencies up to 1.2 cd/A are demonstrated in LEDs prepared with indium–tin–oxide and Ca–Al electrodes.
REFERENCES
1.
G.
Barbarella
, L.
Favaretto
, M.
Zambianchi
, O.
Pudova
, C.
Arbizzani
, A.
Bongini
, and M.
Mastragostino
, Adv. Mater.
10
, 551
(1998
).2.
G.
Gigli
, M.
Lomascolo
, R.
Cingolani
, G.
Barbarella
, M.
Zambianchi
, L.
Antolini
, F.
Della Sala
, A.
Di Carlo
, and Paolo
Lugli
, Appl. Phys. Lett.
73
, 2414
(1998
).3.
T.
Granlund
, M.
Theander
, M.
Berggren
, M.
Andersson
, A.
Ruzeckas
, V.
Sundstrom
, G.
Bjork
, M.
Granstrom
, and O.
Inganas
, Chem. Phys. Lett.
288
, 879
(1998
).4.
M.
Muccini
, E.
Lunedei
, C.
Taliani
, D.
Beljonne
, J.
Cornil
, and J. L.
Bredas
, J. Chem. Phys.
109
, 10513
(1998
).5.
J.
Cornil
, A. J.
Heeger
, and J. L.
Bredas
, Chem. Phys. Lett.
272
, 463
(1997
).6.
D.
Beljonne
, Z.
Shuai
, R. H.
Friend
, and J. L.
Bredas
, J. Chem. Phys.
102
, 2042
(1995
).7.
N. C.
Greenham
, I. D. W.
Samuel
, G. R.
Hayes
, R. T.
Phillips
, Y. A. R. R.
Kessener
, S. C.
Moratti
, A. B.
Holmes
, and R. H.
Friend
, Chem. Phys. Lett.
241
, 89
(1995
).8.
G. Barbarella (unpublished).
9.
J. S.
Kim
, R. H.
Friend
, and F.
Cacialli
, Appl. Phys. Lett.
74
, 3084
(1999
).10.
J. S.
Kim
, M.
Granstrom
, R. H.
Friend
, N.
Johansson
, W. R.
Salaneck
, R.
Daik
, W. J.
Feast
, and F.
Cacialli
, J. Appl. Phys.
84
, 6859
(1998
).11.
G.
Barbarella
, O.
Pudova
, C.
Arbizzani
, M.
Mastragostino
, and A.
Bongini
, J. Org. Chem.
63
, 1742
(1998
).12.
P.
Barta
, F.
Cacialli
, R. H.
Friend
, and M.
Zagorska
, J. Appl. Phys.
84
, 6279
(1998
).13.
S.
Janietz
, D. D. C.
Bradley
, M.
Grell
, C.
Giebeler
, M.
Inbasekaran
, and E. P.
Woo
, Appl. Phys. Lett.
73
, 2453
(1998
).14.
The EL efficiency is usually found to be smaller at higher currents and/or voltages. This may be due to different reasons, namely the degradation of the device under the action of intense currents, or the presence of an excessive number of charged species which may act as quenchers. These effects are relevant in our double layer devices where the EL efficiency shows a high maximum (1.2 cd/A) at low current and luminance followed by a steep decrease at high injection. Work is in progress in order to further optimize the devices.
15.
S. A.
Carter
, M.
Angelopoulos
, S.
Karg
, P. J.
Brock
, and J. C.
Scott
, Appl. Phys. Lett.
70
, 2067
(1997
).16.
F.
Cacialli
, X. C.
Li
, R. H.
Friend
, S. C.
Moratti
, and A. B.
Holmes
, Synth. Met.
75
, 161
(1995
).
This content is only available via PDF.
© 1999 American Institute of Physics.
1999
American Institute of Physics
You do not currently have access to this content.
