light extraction - us department of...
TRANSCRIPT
LIGHT EXTRACTION
The hurdle, OLEDs need to take
Sebastian Reineke [email protected]
(Massachusetts Institute of Technology, Cambridge, MA)
MOTIVATION
$3.6/lm 1
[1] www.lumiotec.com
First panels entering market:
2017 projection : approx. $0.05/lm ¬ Efficiency: > 100 lm/W (10-fold increase) ¬ Cost: panel cost reduction from $355 to $55 (6.5-fold decrease)
1
EFFICIENCY
Technology lm/W Lifetime1 Comments Incandescent bulb 151 1 kh
Halogen 191 2 kh inefficient
CFL 601 10 kh moderate efficiency
Fluorescent tube 90-1002 10 kh poor light quality
Inorganic LED 1043 50 kh point source 1 Steele, Nature Photonics, 2007, 1, 25.
OLED luminous efficacy:
operating voltage light outcoupling internal efficiency
necessities for (white) OLEDs:
2 wikipedia.org, 3 leds.de, retrieved: 2012-01-23.
metal
glass substrate n = 1.51
emission layer
ITO and organics n = 1.7 – 1.8
outcoupled / air mode
substrate mode
organic mode
coupling to metal surface plasmon (SP) field
the four modes in OLEDs
LIGHT MODES
air n = 1
the substrate mode
LIGHT MODES
ideally: pyramids
Reineke et al., Nature, 2009, 459, 234.
lenses
Sun et al., Nature Photonics, 2008, 2, 483.
pillars
Moller et al., J. Applied Physics, 2002, 91, 3324.
2 mm
the organic mode
LIGHT MODES
corrugation
Koo et al., Nature Photonics, 2010, 4, 222.
mode redirection
Sun et al., Nature Photonics, 2008, 2, 483.
Koh et al., Advanced Materials, 2010, 22, 1849.
refractive index matching
Reineke et al., Nature, 2009, 459, 234.
Meerheim et al., Applied Physics Letters, 2010, 97, 253305.
substrate E
TL
interplay of organic and SP modes
LIGHT MODES
n = 1.51
EML
metal
SP field
Furno et al., Proc. SPIE, 2010, 7617, 16.
Higher order devices with refractive index matched substrates
Reineke et al., Nature, 2009, 459, 234.
LIGHT MODES
escape cone
Higher order devices with refractive index matched substrates
Reineke et al., Nature, 2009, 459, 234.
LIGHT MODES
low versus high refractive index substrate
1st versus 2nd field antinode on high index substrates
TOP EMITTING OLEDs
transparent (glass)
organic metal
B opaque (metal)
organic metal
T
dielectric
opaque (metal)
organic metal
T
Thomschke et al., Applied Physics Letters 2009, 94, 083303.
Cheap alternative with complex optics. ¬ outcoupling enhancement hard to achieve
¬ strong color changes with increasing viewing angle
¬ conventional substrate surface modification not applicable
TOP EMITTING OLEDs
Thomschke et al., Nano Letters 2012, 12, 424.
without microlens foil with microlens foil
TOP EMITTING OLEDs
Thomschke et al., Nano Letters 2012, 12, 424.
some numbers: ¬ 30 lm/W at 1000 cd/m2
¬ CRI of 93 with CIE (0.472, 0.430)
SUMMARY
Bottom-emitting OLEDs: ¬ extracting substrate modes is trivial
¬ various concepts exist to efficiently couple out organic modes (cheap process integration is key to determine successful path) ¬ strong losses in OLEDs due to coupling to metal surface plasmon modes
• spacing EML and cathode is very efficient to suppress coupling • however, increasing ETL increases organic modes with overall small benefit • organic and SP mode extraction should be considered a coupled system
Top-emitting OLEDs: ¬ typically complex optical systems (micro-resonator) with detrimental properties for white OLEDs ¬ lamination of refractive index matched microlens film achieves efficient outcoupling enhancement and color mixing