10.1021/ma021165q.s001
Nam Seob Baek
Nam Seob
Baek
Hwan Kyu Kim
Hwan Kyu
Kim
Eun Hee Chae
Eun Hee
Chae
Byeang Hyean Kim
Byeang Hyean
Kim
Ji-Hoon Lee
Ji-Hoon
Lee
Exploratory Synthesis and Luminescence Study of the First
π-Conjugated Tin-Based Alternating Copolymers for
Blue Light-Emitting Diodes at the Very Low Operating Voltage<sup>†</sup>
American Chemical Society
2002
PAF
PPP
EL
eV
efficiency
UV
LUMO level
HOMO
blend
PVK
cyclic voltammetric studies
ITO
LED
polymer
wavelength 350 nm
device
2002-11-06 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Exploratory_Synthesis_and_Luminescence_Study_of_the_First_-Conjugated_Tin-Based_Alternating_Copolymers_for_Blue_Light-Emitting_Diodes_at_the_Very_Low_Operating_Voltage_sup_sup_/3731592
Tin-based alternating copolymers with a uniform π-conjugated segment were synthesized
using the Heck reaction between distyrylstannane monomer and various difunctionalized monomers.
The UV−vis absorption maximum peaks of the resulting polymers in chloroform solution and in thin
films appeared in the wavelength range of 347−394 nm. Upon photoexcitation with light of wavelength
350 nm, their photoluminescence spectra exhibited an emissive maximum peak around 470−502 nm,
corresponding to blue light emission. Multilayered light-emitting diodes with ITO/PEDOT (50 nm)/polymer
(80 nm)/Ca (50 nm)/Al (200 nm) composition were fabricated. These LED devices exhibited an emissive
maximum peak in the range of 464−472 nm. All of the materials exhibited a very low turn-on voltage of
less than 4 V. From cyclic voltammetric studies and optical data, the LUMO level is estimated to be 3.20
eV for SnPhFPV and 2.90 eV for SnPhPVK, and the ionization potentials (HOMO level) were estimated
to be 5.90 eV for SnPhFPV and 5.60 eV for SnPhPVK. This lowered LUMO level, in comparison to those
of poly(<i>p</i>-phenylene) derivatives (such as PPP, ladderlike PPP, and PAF), reduces the energy barrier to
electron injection, resulting in a lowering of the operating voltage in the polymeric LED. Compared to
devices based on the tin-based polymers alone, devices based on blends between the tin-based polymers
and PVK showed improved efficiency of power and luminescence by at least 2−4 times and 3−6 times,
respectively. Also for these polymer:PVK blends, the electroluminescence efficiency enhances up to the
range of 0.1−0.3 lm/W, and the purity of the emitted blue color improves. These results may be attributed
to the intramolecular confinement by diluting the EL polymers with PVK. One of the devices based on
a blend system between a tin-based polymer and PVK has a brightness of 2047 cd/m<sup>2</sup> at 11 V with a
power efficiency of 0.3 cd/A.