HTL ; c Ó Þ3 ûÀ W ¥ ¥M $ [Ä Z Ø ö n Úù m Ç NPB U c lT c l8 ý ° Ë Ñ] K ¡X ì Ä V R Ëù m Ç
' å r )
Å Ò@ / < Æ § ¸·& ñ ÐÖ 6 x ½ + Ël Õ ü t ½ ¨ è, Ã º" é ¶ 443-749
Õ* å
Å Ò@ / < Æ § \ -t r Û ¼% 7 < ÆÂ Ò, Ã º" é ¶ 443-749
T
) Ö < G B ∗ · z £ Ó
Å Ò@ / < Æ § \ -t r Û ¼% 7 < ÆÂ Ò, ¸·& ñ ÐÖ 6 x ½ + Ël Õ ü t ½ ¨ è, Ã º" é ¶ 443-749 (2008¸ 4 Z 4 8{ 9 ~ Ã Î6 £ §)
ª / B N s 1 l x5 Å q ¸ À 1 Ï 8 £ x ½ ¨ ¸ OLED\ " f ª / B N Å Ò{ 9 8 £ x (HIL : hole injection layer) s ª / B N Ã º5 Å x 8
£ x (HTL : hole transport layer) Ó ü t| 9 Ð ´ ú §s 6 x ÷ &# Q : r Ä »l $ ì r NPB(N,N
0-bis(1-naphthyl)- N,N
0- diphenyl-1,1’
0-biphenyl-4,4
0-diamine)\ ¦ z ´o B H õ _ þ t s × ¼Ä »o l ó ø Í0 A\ 2 × 10
−6Torr _ /
B
N \ " f \ P 7 £ x à Ìl \ ¦ s 6 x # 1.0 ˚ A/sec _ 5 Å q ¸ Ð 7 £ x Ã Ì % i . / B N7 £ x à ÌZ O Ü ¼ Ð é ß { 9 ~ à Ì} ] j Ê ê 1.5
∼ 4.5 eV F g \ -t % ò % i \ " f ì rF g " é ¶ K $ 3 Û ¼& 7 à Ô! 3 ` ¦ 8 £ ¤& ñ · ì r$ 3 # NPB_ F g < Æ © Ã º_ ° ú כ` ¦
& ñ % i . ì r$ 3 \ H Jellison Modine ì r í ß ' a > d \ Bruggeman_ Ä »´ òB | 9 s : r` ¦ 8 # / B N l /~ Ã Ì }
+/ B NF G (void)/ l 8 £ x _ 3 © > ¸4 S q` ¦ & h 6 x r ( . & ñ ) a F g < Æ © à º H 8 £ ¤& ñ ) a f ¨F g ¸ü < è F g > à º Ð Â
Ò' > í ß ) a f ¨ Ã º> Ã º_ q § Ð 7 £ x % i . 8 £ ¤& ñ ô Ç PL Û ¼& 7 à Ô! 3 ` ¦ Gaussian function Ü ¼ Ð ì r K
#
f ¨F g ¸ü <_ Ö ¦ © ¸ S X % i .
PACS numbers: 74.25.Gz, 78.20.Ci, 78.55.-m
Keywords: Ä »l µ 1 Ï F g s ¸× ¼, NPB, Jellison Modine ì r í ß ' a > d , F g < Æ © à º
I. " e  ] Ø
Ä
»l µ 1 Ï F g s ¸× ¼ (organic light emitting diodes : OLED) H Ä »l F « Ñ\ > \ ¦ # l \ -t \ ¦ y n C Ü
¼ Ð Ë ¨# QÅ Ò H è Ð" f, ª F G õ 6 £ §F G s \ Ä »l ~ Ã Ì }
8 £ x s e H ½ ¨ ¸\ ¦ l : r Ü ¼ Ð ¦ e . ª F G \ H ITO (indium tin oxide) ü < ° ú É r È Ò" î F G` ¦, 6 £ §F G \ H { 9 < ÊÃ º
± ú É r Ca, Al, Mg ü < ° ú É r F K5 Å q` ¦ 6 x ô Ç . { 9 ì ø Í& h Ü ¼ Ð l
ó ø Í É r Ä »o \ ¦ 6 x t ë ß ½ ¨Â Òw n = à º e H e ¦ Û ¼h Ë :s PET 9 2 £ § 1 p x` ¦ 6 x ½ + É Ã º ¸ e [1]. Ö ¦ Q OLED H
^ µ 1 Ï F g, ¦5 Å q6 £ x ² ú , F g r y , í~ Ã Ì+ þ A, ¦ o| 9 , ? /½ ¨$ í , V ,
É r : r ¸# 3 0 A 1 p x 21 [ jl ' é ß í ß \ O r @ /_ n Û ¼e ¦ Y Us
\
כ ¹½ ¨÷ & H : £ ¤$ í [ þ t` ¦ ¿ ºÀ Ò ° ú Æ Ò ¦ e # Q TFTü < LCD\ ¦
@
/^ ½ + É s © & h n Û ¼e ¦ Y Us Ð y F g ~ Ã Î ¦ e . OLED _
> hµ 1 Ï É r y n C_ 3" é ¶Ò o R.G.B\ K { © H é ß Ò o OLEDü <
Ñ þ
Ò o OLED × æd Ü ¼ Ð > hµ 1 Ïs ' ÷ &# Q Ò o (full color)
∗
E-mail: [email protected]
OLED Ð S X © ÷ &% 3 . { 9 ì ø Í& h Ü ¼ Ð OLED_ µ 1 Ï F g É r µ 1 Ï F g 8
£
x \ 6 x ÷ & H Ä »l Ó ü t _ : £ ¤$ í \ _ K & ñ ) a .
OLED _ 1 l x ´ òÖ ¦` ¦ ¾ Ó © r v l 0 AK " f H ¦´ òÖ ¦ µ 1 Ï F
gÓ ü t| 9 _ s 6 x õ 8Ô ¦ # Q è _ l & h · F g < Æ& h 1 l x ` ¦
¦ 9ô Ç è ½ ¨ ¸ þ j& h o 9 כ ¹ . 8 £ x ½ ¨ ¸ Ð s À Ò
#
Q OLED_ F g : £ ¤$ í É r × æ ç ß [ O ` ¦ ¦ 9ô Ç Fresnel d Ü
¼ Ð è q à º e Ü ¼Ù ¼ Ð, è \ ¦ ½ ¨$ í H y Ó ü t| 9 [ þ t _ 4
¤ èÏ ã J] X Ò ¦ ë ß · ú è ? / Ò\ " f ë ß [ þ t # Q y n C` ¦ þ j@ / ô
Ç ã ¼| 9 # Q è q à º e H F g ½ ¨ ¸ [ O > 0 p x . ~ à Ì} _ 4
¤ èÏ ã J] X Ò ¦ & ñ É r F g < Æ& h 8 £ ¤& ñ x 9 ì r$ 3 ` ¦ : x K 0 p x 9 [2–4], Ò oí H ¸ Z } É r ¦´ òÖ ¦ _ è \ ¦ ] j l 0 AK F
g < Æ& h / B N ½ ¨ ¸\ @ /ô Ç ½ ¨ ¸ ´ ú §s Ð ¦÷ & ¦ e [5, 6].
OLED \ @ /ô Ç F g < Æ& h / B N ½ ¨ ¸\ ¦ ½ ¨ & ³ # Z } É r Ò o í
H ¸ x 9 ¦´ òÖ ¦ _ è \ ¦ ½ ¨ & ³ l 0 AK " f H è ] j
\ 9 כ ¹ô Ç y 8 £ x Ó ü t| 9 _ ¿ ºa F g < Æ © Ã º 1 p x` ¦ p o
& ñ # í ß r Ð 3 x` ¦ : x ô Ç þ j& h _ ¸| ` ¦ ¹ 1 Ô ? / H õ
&
ñ s ' ÷ &# Q ô Ç . Õ ªA " f : r ½ ¨\ " f H ´ ú § É r ~ ½ Ó
¾ Ó7 á ¤ l u ¨ 8 ) a À Ó Ð ª / B N _ s 1 l x5 Å q ¸ _
-512-
Fig. 1. Chemical structure of NPB.
s
1 l x5 Å q ¸ Ð 10
3& ñ ¸ & " f HTL (hole transport layer) \ 6 x ÷ &# Q ª / B N s 1 l x s ~ 1 ¸2 ¤ ¸ü <Å Ò ¦ 2 ;
o ¸ _ s 1 l x` ¦ ] j# Qô Ç ¦ Ð ¦÷ & H Ä »l
$
ì r Ó ü t| 9 NPB (N,N
0-bis (1-naphthyl)-N,N
0-diphenyl- 1,1
0-biphenyl-4,4
0-diamine) [7–10] ~ Ã Ì} _ F g < Æ © Ã º & ñ x 9
F g µ 1 Ï F g (PL : photoluminescence) õ PLE (PL excita- tion) _ ' a > 1 p x l í F g < Æ& h : £ ¤$ í ` ¦ ½ ¨ % i . 3.0 eV _ \ -t ½ × ¼Ì s (E
g) [11–13]` ¦ t H NPB ~ Ã Ì} \
@
/ô Ç ì rF g " é ¶ Û ¼& 7 à Ô! 3 ` ¦ 8 £ ¤& ñ , ì r í ß ' a > d õ Ä »´ òB | 9 s
: r` ¦ 6 x # 8 £ ¤& ñ õ \ ¦ þ j& h ´ ú » ¡ § H ì r$ 3 ~ ½ ÓZ O
`
¦ G × þ % i [14–17]. & ñ ) a F g < Æ © Ã º_ & ñ S X $ í É r 8 £ ¤
&
ñ ) a f ¨F g ¸ü < è F g > à º РÒ' > í ß ) a f ¨ à º> à ºü <_ q
§ Ð 7 £ x % i .
II. ÷ m Ç] M ö U ê s0 n É
1. M m Ç U ØR õ m Í mø m ÇU c lT c l < gX c l
~ Ã
Ì} 7 £ x à Ì\ 6 x ) a l ó ø Í[ þ t É r 6 £ § _ õ & ñ ` ¦ 5 g ï r q
% i . 1 mm ¿ ºa _ _ þ t s × ¼Ä »o ü < ô Ç s e ¦ o d ç
)
a 525±10 µm ¿ ºa _ (100) z ´o B H J ?s ( \ ¦ 1 inch × l inch ß ¼l Ð ¸ ú | 9 èÛ ¼ Ð t \ ¦ ± ú 2 ; Ê ê [ j : r, IPA (isopropanol alcohol), 7 £ x À ÓÃ º_ í H " f Ð y 5ì rm í 6
£
§ [ j' % i . Õ ªo ¦ | 9 è Û ¼ Ð ³ ð _ Ó ü t` ¦ ] j ô
Ç Ê ê, | 9 è ì r 0 Al _ / å J QÚ Ô ~ à ÌÛ ¼î ß \ ~ à Ì} 7 £ x à Ì` ¦ 0 AK V ,
# Q ¿ º% 3 .
Fig. 1 _ o < ƽ ¨ ¸\ ¦ t H Ä »l $ ì r Ó ü t| 9 NPB r
«
Ñ\ ¦ ï r q % i (Fig. 1). r « Ñ_ 7 £ x à Ì\ H Fig. 2 \
Ð \ P 7 £ x à Ìl (thermal evaporator)\ ¦ s 6 x, NPB r « Ñ
\
¦ $ 3 % ò ¸m \ 40 mg | ¾ Ó { 7 £ x à Ì\ 6 x % i .
7
£
x à Ìl ? / Ò\ H 8 ú x 5 > h_ Ðà Ô e . NPB é ß { 9 ~ à Ì}
É
r ï r q ) a _ þ t s × ¼Ä »o ü < z ´o B H l ó ø Í0 A\ 1 l x r \ 2 × 10
−6Torr _ / B N× æ \ " f 3 Ðà Ô\ " f 1.0 ˚ A/sec _ 5 Å q ¸
Fig. 2. Glove box and inner schematic of thermal evap- orator equipment.
Ð 50 nm & ñ ¸ ¿ ºa _ é ß { 9 ~ Ã Ì} Ü ¼ Ð 1 l x{ 9 ¸| \ " f 7 £ x
Ã
Ì Ê ê / å J QÚ Ô ~ à ÌÛ ¼î ß \ " f x 9 ` # F g < Æ 8 £ ¤& ñ r t Ð
'
a % i (Fig. 2).
2. ÷ m Ç] M ö© ¤X N Ë
z
´o B H l ó ø Í0 A\ 7 £ x Ã Ì ) a NPB é ß { 9 ~ à Ì} \ @ / # z ´
: r \ " f { 9 y ì rF g " é ¶ > (variable angle spectro- scopic ellipsometer : VASE, J. A. Woollam Co.)\ ¦ 6
x # , { 9 y 65
◦, 70
◦, 75
◦y y \ " f 0.05 eV ç ß Ü ¼
Ð F g \ -t % ò % i 1.5 ∼ 4.5 eV\ @ / # " é ¶ y ∆ü <
Ψ\ ¦ 8 £ ¤& ñ % i . _ þ t s × ¼Ä »o 0 A\ 7 £ x Ã Ì ) a NPB ~ à Ì} \
@
/ # H ì rF gF g ¸> (spectrophotometer, Jasco model V-570)\ ¦ 6 x # f ¨F g ¸\ ¦ 8 £ ¤& ñ % i ¦, 150 W Xenon lamp\ ¦ # l F g " é ¶ Ü ¼ Ð H ì rF g+ þ AF g > (spectrofluorom- eter, Jasco model FP-6500)\ ¦ 6 x # PL x 9 PLE [ j l
\ ¦ 8 £ ¤& ñ % i . PL 8 £ ¤& ñ r # l © É r f ¨F g ¸_ 4 x Ä
ºo 345 nm Ð % i ¦, PLE 8 £ ¤& ñ r µ 1 Ï F g © É r PL 4
x Ä ºo 440 nm Ð % i .
III. ÷ m Ç] M ö+ s ÇÊ Ý õ m Í Ä Z ØV Ä
Fig. 3 \ _ þ t s × ¼Ä »o l ó ø Í0 A\ 50 nm ¿ ºa Ð 7 £ x Ã Ì ) a
NPB é ß { 9 ~ Ã Ì} \ @ / # ì rF gF g ¸> ü < ì rF g+ þ AF g > \ ¦
Fig. 3. Comparison of absorbance(right) and the best -fit PL spectra with Gaussian function (left).
Fig. 4. The measured (symbols) and the best-fit (solid lines) SE spectra measured at three different incident angles of NPB film.
6
x # 8 £ ¤& ñ ô Ç f ¨F g ¸ü < PL Û ¼& 7 à Ô! 3 ` ¦ q § #
?
/% 3 . f ¨F g ¸ H 345 nm (: 3.59 eV), PL Û ¼& 7 à Ô! 3 É r 440 nm (:2.82 eV)\ " f 4 x Ä ºo \ ¦ Ð# f ¨F g ¸\ @ / # PL Û ¼& 7 à Ô! 3 _ & h Ò o¼ # s (red-shift, Stokes Shift) & ³ ©
`
¦ S X % i . f ¨F g ¸ Û ¼& 7 à Ô! 3 \ ] X ` ¦ Õ ª# Q ¶ ú ( R : r F
g \ -t (photon energy, eV)\ @ /ô Ç \ -t ½ × ¼Ì s (E
g) É r 412 nm (: 3.01 eV) Ð Ã Ð ¦ 7 Hë H [15–17] _ 3.0 eV ü < _ { 9 u % i (Fig. 3).
Fig.3 _ ý a8 £ ¤ PL Û ¼& 7 à Ô! 3 É r ß ¼l \ ¦ 1 Ð & ñ ½ © o # 4
x Ä ºo + þ AI Ä ºÛ ¼ < ÊÃ º (Gaussian function)\ ¦ ë ß 7 á ¤ ô Ç
¦ & ñ ¦, èá Ôà ÔJ ?# Q ¸o ! Q 7.5\ ¦ s 6 x, þ j
&
h ´ ú » ¡ § [18,19]` ¦ : x # 4 x Ä ºo \ ¦ ì r K ô Ç כ s . õ 3 > h Ð ì r K ÷ &% 3 Ü ¼ 9, þ j& h ´ ú » ¡ § ) a 4 x Ä ºo H 2.645, 2.796, 2.913 eV Ð ¸¿ º ' õ AÒ o % ò % i s % 3 ¦, [ jl _ q H 0.135, 0.187, 0.067 Ð z ¤ . z ´ Ü ¼ Ð ³ ðr ô Ç [ j > h_ f ¨ F
g ¸ 4 x Ä ºo \ ¦ Ð 3.297, 3.594, 3.948 eV Ð 4 x Ä ºo ç ß
s 0.296, 0.355 eV Ð · ú ¡" f ì r K ) a PL 4 x Ä ºo ç ß 0.151, 0.117 eV ü < Ö ¦ © (mirror image)` ¦ Ðe ` ¦ · ú Ã
º e [20–22].
Fig. 5. Optical-constants spectra of NPB corresponding to the respective best-fit spectra in Fig. 4. The inset presented is Tauc’s plot for a NPB film.
Fig. 6. Comparison of the measured absorbance with the calculated absorption-coefficient spectra.
Fig. 4 H z ´o B H l ó ø Í 0 A\ 7 £ x Ã Ì ) a NPB é ß { 9 ~ à Ì} \
@
/ # VASE\ ¦ 6 x # 1.5 ∼ 4.5 eV_ F g \ -t % ò
%
i \ " f { 9 y 65
◦, 70
◦, 75
◦y y \ @ / # 0.05 eV ç ß Ü
¼ Ð 8 £ ¤& ñ ô Ç " é ¶ y ∆ü < Ψ_ Û ¼& 7 à Ô! 3 ` ¦ þ j& h ´ ú » ¡ §
#
· p כ s . ∆ü < Ψ_ 8 £ ¤& ñ ° ú כ\ @ /ô Ç þ j& h ´ ú » ¡ §` ¦ 0
AK " f / B N l /~ Ã Ì} +/ B NF G/ l 8 £ x _ 3 © > ¸4 S q` ¦ & h 6 x % i
(Fig. 4).
" é ¶ y ∆ü < Ψ Û ¼& 7 à Ô! 3 _ þ j& h ´ ú » ¡ § É r Levenburg- Marquadt · ú ¦o 7 £ §` ¦ s 6 x ô Ç + þ A r) ì r$ 3 ` ¦ : x #
© l 3 © > ¸4 S q\ > í ß ) a " é ¶ y Û ¼& 7 à Ô! 3 õ 8 £ ¤& ñ
° ú
כ_ s \ ¦ × ¦ # H ~ ½ ÓZ O Ü ¼ Ð s À Ò# Q& . " é ¶ y Û ¼
&
7 à Ô! 3 _ > í ß É r y 8 £ x _ ¿ ºa ü < 4 ¤ èÏ ã J] X Ò ¦ ë ß · ú
×
æ ç ß [ O ` ¦ ¦ 9ô Ç Fresnel d ` ¦ s 6 x # ç ß é ß y ½ + É Ã º e
.
s
ì r$ 3 \ " f NPB_ 4 ¤ èÏ ã J] X Ò ¦ É r Jellison Modine ì
r í ß d [23]` ¦ ë ß 7 á ¤ ô Ç ¦ & ñ % i ¦, NPBü < / B NF G Ü ¼ Ð s
À Ò# Q 8 £ x _ 4 ¤ èÏ ã J] X Ò ¦ É r Bruggeman _ Ä »´ òB | 9 H
(effective medium approximation : EMA) [24]\ ¦ 6 x
# ? /% 3 . Fig. 4\ " f Ð H ü < ° ú s NPB ~ Ã Ì}
_
∆ü < Ψ 8 £ ¤& ñ ° ú כõ ´ ú » ¡ § > í ß ) a Û ¼& 7 à Ô! 3 É r _ { 9 u
¦ e Ü ¼ 9, s H þ j& h ´ ú » ¡ § õ & ñ s Å Ò ¸ ú s À Ò# Q& 6 £ §
`
¦ _ p ô Ç . F g < Æ& h Ü ¼ Ð ì r$ 3 ) a ~ Ã Ì} _ Ä »´ òB | 9 8 £ x ¿ º a
H 69.1±0.19 nm, / B NF G Â Òx H 24 % Ð ì r$ 3 ÷ &% 3 Ü ¼ 9 z
´] j 7 £ x à Ìô Ç ¿ ºa ü < _ { 9 u % i .
Fig. 4 _ þ j& h ´ ú » ¡ § õ \ @ /6 £ x ÷ & H Jellison Modine ì r í
ß d > Ã º[ þ t` ¦ s 6 x # & ñ ) a NPB _ Ï ã J] X > Ã º n(λ)õ
è F g > Ã º k(λ)_ Û ¼& 7 à Ô! 3 ` ¦ Fig. 5 \ ? /% 3 (Fig.
5). è F g > Ã º_ 4 x Ä ºo 347 nm Ð & ñ ÷ &# Q Fig. 3_ f
¨F g ¸ 4 x Ä ºo 345 nmü < _ { 9 u H כ Ü ¼ Ð Ð
& ñ ) a F g < Æ © Ã º\ ¦ ø @½ + É Ã º e % 3 . Õ ªo ¦ & ñ
)
a F g < Æ © Ã º Ð f ¨ Ã º> Ã º\ ¦ ½ ¨ô Ç Ê ê Tauc plot` ¦ & h 6 x r
&
√
α · E\ ¦ F g \ -t \ @ / # · p Û ¼& 7 à Ô! 3 ` ¦ Fig.4 î ß \ ¶ ú { 9 % i [25-27]. Õ ªa Ë >_ + þ AÂ Òì r` ¦ ô
Ç s t H x ] X ¼ # ` ¦ Ð E
g H 2.92 eV Ð 8 £ ¤& ñ ô
Ç Fig. 3 f ¨F g ¸\ " f_ E
g3.01 eV (: 412 nm)ü < ç ß
s \ ¦ Ð% i .
& ñ ) a NPB F g < Æ © Ã º_ & ñ S X $ í ` ¦ 7 á § 8 & ñ | ¾ Ó& h Ü ¼ Ð S X
l 0 A # z ´o B H l ó ø Í\ 7 £ x Ã Ì ) a ~ à Ì} _ â Ä º È Ò õ
Ö ¦ 8 £ ¤& ñ s Ô ¦ # z ´o B H l ó ø Íõ 1 l x{ 9 ¸| \ " f 1 l x r
\ 1 l x{ 9 ¿ ºa Ð _ þ t s × ¼ Ä »o l ó ø Í0 A\ 7 £ x Ã Ì ) a NPB é
ß { 9 ~ Ã Ì} \ @ / # ì rF gF g ¸> \ ¦ 6 x # 8 £ ¤& ñ ô Ç f ¨F g
¸ü < Fig. 5\ " fü < ° ú s & ñ ) a è F g > à º\ ¦ s 6 x ô Ç f ¨ à º
>
à º\ ¦ q § # Fig. 6\ ? /% 3 (Fig. 6). f ¨ à º> Ã
º 4 x Ä ºo 344 nm Ð 8 £ ¤& ñ ) a f ¨F g ¸ 4 x Ä ºo 345 nmü <
¸ ú
{ 9 u % i ¦, f ¨ Ã º> Ã º_ Û ¼& 7 à Ô! 3 \ ] X Ü ¼ Ð
· p Eg ¸ 3.01 eV (: 412 nm) Ð Fig. 3_ E
gü < { 9 u ô Ç כ Ü
¼ Ð Ð F g < Æ © Ã º & ñ S X > & ñ ÷ &% 3 6 £ §` ¦ 7 £ x % i
.
IV. + s Ç Â ] Ø
8 £ x _ OLED\ ª / B N _ s 1 l x5 Å q ¸ _ s 1 l x5 Å q ¸
Ð & " f HTL Ó ü t| 9 Ð ´ ú §s 6 x ÷ & H Ä »l $ ì r Ó ü t| 9 NPB _ F g < Æ © Ã º\ ¦ { 9 y ì rF g " é ¶ K $ 3 Û ¼& 7 à Ô! 3
`
¦ ì r$ 3 # & ñ % i . & ñ ) a NPB F g < Æ © Ã º_ & ñ S X
$ í
É r f ¨ à º> à ºü < f ¨F g ¸ 8 £ ¤& ñ õ _ q § РÒ' S X
% i . Ö ¦ Q PL Û ¼& 7 à Ô! 3 ` ¦ 8 £ ¤& ñ · ì r$ 3 # f ¨F g ¸ _
4 x Ä ºo ü < @ /| Ä Ì& h Ö ¦ © ` ¦ s ê r H z ´ ¸ S X
% i . s ü < ° ú É r ì r$ 3 ~ ½ ÓZ O Ü ¼ Ð l > r _ Á ºl ì ø Í ¸^ \
"
fü < ð ø Ít Ð Ä »l $ ì r ~ Ã Ì} _ F g < Æ © Ã º ¸ & ñ
½
+ É Ã º e % 3 . 8 £ x ½ ¨ ¸_ OLED H µ 1 Ï F g8 £ x \ " f ü <
ª / B N _ ½ + Ë\ _ K ë ß [ þ t # Qt H y n C` ¦ è µ 1 ÚÜ ¼ Ð ~ ½ ÓØ ¦ r
v H X < è ½ ¨ ¸\ É r × æ ç ß [ O ´ òõ \ ß ¼>
² ú
. " f OLED_ F g < Æ& h 1 l x ` ¦ ¦ 9ô Ç è
½
¨ ¸ þ j& h o כ ¹½ ¨÷ & 9, s \ ¦ 0 AK " f H è \ ¦ ½ ¨$ í
H y Ó ü t| 9 [ þ t _ F g < Æ © Ã º & ñ Ð 9 Ã º& h s . Á ºl ì ø Í ¸
^
Ä » ^ Ó ü t| 9 õ H ² ú o Ä »l Ó ü t| 9 [ þ t \ @ /K " f H F g
< Æ © Ã º ¸ ú · ú 94 R e t · ú § : r 7 Hë H _ ì r$ 3 ~ ½ ÓZ O ` ¦ 6
x # Q " Ä »l $ ì r ¦ì r _ F g < Æ © à º ¸ & ñ S X
>
& ñ ½ + É Ã º e ¦, & ñ ) a F g < Æ © Ã º\ ¦ s 6 x # OLED 8
£
x ¿ ºa o\ É r EL x 9 F g < Æ& h / B N ½ ¨ ¸ l © 1
p
x _ í ß r Ð 3 x Ü ¼ Ð OLED_ ª ´ òÖ ¦` ¦ 7 £ x r v H X <
¸ 6 £ x6 x 0 p x o l @ /ô Ç .
Y
c p w à U Ø ô
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Optical Properties of NPB Used as HTL Material
Myung Hee Park
NT·IT Fusion Technology Institute, Ajou University, Suwon 443-749
Hyo Yeong Park
Division of Energy Systems Research, Ajou University, Suwon 443-749
Soonil Lee
∗and Ken Ha Koh
Division of Energy Systems Research, NT · IT Fusion Technology Institute, Ajou University, Suwon 443-749 (Received 8 April 2008)
An organic small molecule, NPB (N,N
0-bis (1-naphthyl)-N,N
0-diphenyl-1,1
0-biphenyl -4,4
0- diamine), has been used as the main material for a hole injection layer (HIL) or hole transport layer (HTL) in organic light-emitting diodes (OLEDs) multi-structure due to its high hole mobility.
The NPB thin film was deposited on Si and glass substrates by using a thermal evaporator in a vacuum of 2 × 10
−6Torr at a deposition rate of 1.0 ˚ A/sec. We determined the optical constants of the as-deposited film through by analysis of the ellipsometric spectra measured at three different incident angles in the photon-energy range of 1.5 ∼ 4.5 eV. For the analysis, we used Jellison- Modine dispersion function and Bruggeman’s effective medium approximation, and we assumed a three-phase model of air/film+void/substrate. The accuracies of the determined optical constants were confirmed by comparing the measured absorbance of the NPB films on glass substrates with the absorption coefficient which was calculated using the determined extinction coefficient. Decon- volution of the PL spectrum based on Gaussian functions confirmed that the PL spectrum was the mirror image of the absorbance spectrum.
PACS numbers: 74.25.Gz, 78.20.Ci, 78.55.-m
Keywords: OLED, NPB, Jellison Modine dispersion function, Optical constants
∗
