Arjan Langen - TNO/Holst Centre

Large area coating for
flexible electronics
Arjan Langen TNO/Holst Centre

Themadag Mikrocentrum :
Organic and printed electronics

23 November 2012

Large area coating for
flexible electronics
• OLED
• OPV
• R2R manufacturing
• Web handling
• Slot die coating
• Contamination control
• Summary
• Holst Centre Large area printing

Presentation
overview

OLED - Organic light emitting diode

Organic and printed electronics 23 Nov 2012

© Holst Centre  5

OLED Lighting: relevant to society and economy

19% of all generated electricity goes to lighting

If OLED has 10% share in replacement market for lighting:
100.000.000 m2 OLEDs/year needed



2009: First OLED lamps for sale on glass



OLED Lighting / Signage OLED Display
• Price competitive against: incandescent • High prices for high-end
light bulb, fluorescent, non-organic led market (telephones, TV’S,
• Pursue pixels as big as possible for monitors)
more efficient light output • Pursue pixels as small as
possible for better
resolution

Large size flexible OLED for lighting/signage
OLED Display



Why Flexible OLED?
• Rollable, wearable, ultra-thin, low-weight, unbreakable
• Easy integration in walls, ceilings, windows, cars etc.
• Light color can be tuned
• Enabling large area, low-cost R2R production
• GOAL:
R2R production for <100 €/m2 and 50 lm/W @ LT70=10kh in
2016 (light bulb 12 lm/W, fluorescent 55 lm/W)

In bodywork integrated OLED OLED for lighting/signage



Why Flexible OLED?

“Hammer test” OLED


Presentation
overview

OPV –Organic photo voltaic


© Holst Centre 

Solar power: omnipresent

Solar radiation on earth sphere
5,000,000 ExaJoule/year

Global energy
consumption circa
500 ExaJoule/Year


© Holst Centre 

Capturing 0,01%
covers total energy need

Requires 750.000 km2 present day solar
cells
(Surface area of Spain = 500.000 km2 )
Present world wide installation <200 km2


© Holst Centre 

Improving efficiencies

Source: NREL National renewable energy laboratory www.nrel.gov;


Why Flexible OPV?
• Rollable, wearable, ultra-thin, low-weight, unbreakable
• Easy integration into walls, roofs, tents, mobile phones etc.
• No use of scares metals (Cd, Te, In, Ga, Se, As, Mo)
• Enabling large area, low-cost R2R production
• Goal:
R2R production for <50 €/m2 and >10% efficiency in 2016 (<0.5
€/Wp )

Roll to roll produced silver cathode Former generation OPV cells


Presentation
overview

R2R manufacturing



Lay out of the “bottom emissive“ OLED or OPV
stack
• Top Encapsulation to prevent water vapor / oxygen
• Cathode
• Functional layer 0,08-0,3µm
(human hair≈0,02-0,2µm)
 OPV: PAL = Photon Absorbing Layer
 OLED: LEL = Light Emitting Layer
• Anode
• Metal grid to support surface
power distribution/collection
• Moisture barrier prevent
water vapor / oxygen
• Foil = Transparent

Because of Ohms Law functional layer
should be:
• Homogeneous in film thickness

Schematic overview of OLED/OPV stack


 17
© Holst Centre
17

Inspection Inspection Inspection

Example of Foil quality Particles Coating defects
Defects Layer thickness
Optical constants

manufacturing foil

process
substrate
production
Barrier deposition
half-
SiN/OCP/SiN product

Cleaning?

Cleaning? Repair?

Plasma Cleaning Inspection Inspection Inspection Inspection
surface energy Coating Coating defects Coating defects Coating defects
Inspection defects Layer thickness Layer thickness Layer thickness
particles Plasma
defects in barrier Cleaning
Repair
surface


energy
metal grid organic organic organic
(printing) layer I layer II layer n

Cleaning? Cleaning?
Inspection in dry and/or
wet layer?

Target processes for mass production:
Vacuum and/or non vacuum R2R / S2S Vacuum / N2 atmosphere
Inspection Inspection Inspection
electrical defects Coating defects device
Repair Layer thickness performance
Cost modeling clearly shows that R2R hard shorts

only is more efficient if:
Barrier deposition OLED
• Yield process step is very high(>95%) Cathode
(evaporation)
end-
SiN/OCP/SiN product
In situ monitoring a necessity
Inspection ?
• Homogeneity requirement of OLEDs Particle
(local)
contamination
favor slot die coating but patterning Cleaning? Cleaning? Repair?

in tiles not straight forward.



R2R equipment for OLED or OPV manufacturing
Anode deposition +
Barrier Production Metal grid production Functional layers +
Cathode deposition

Roll to Roll barrier tool Roll to Roll flash sintering Roll to Roll coating line
- Length 6 meter, 33ton - Length 10 meters - Length 14 meters
- Width web 30-42 cm - Width web 30-40 cm - Width web 30-50 cm
- Speed 0,1-5m/min - Speed 1-20 m/min - Speed 3-30 m/min
- PECVD - Screen and inkjet printing - Slot die coating technology
- Organic/anorganic - Metal sintering by flash - Intensive air drying
deposition
- Cleanroom compatible - Cleanroom compatible
- Vacuum



Roll to Roll coating line
Splice Re-winder
Un-winder
30-60cm wide
Corona
Surface- Schematic overview table 30-60cm wide
500mtr long treatment 500mtr long

Tacky roller for
Contamination Coating/print Hot Air Dryer Foil laminating unit
control Station 25-250°C
- Modular - 5000m3/hour

Stirring unit
Stirring unit


Presentation
overview

Web Handling



Roll to roll manufacturing:
Production of a device on a flexible carrier or substrate (web) by rolling off and on.
This is a very efficient way of production and transporting of large area
materials.

For R2R production you need of web handling.

Web handling: Art and science of getting a web through a machine as
fast/wide as possible with a minimum of waste.

Force is applied on a web to induce tension

Strain in tensioned
web
Stress-strain curve of Examples of E-
plastic web modelus



Web handling

Why do we need tension with web handling
• Tensioning creates friction against rollers necessary for traction especially
in the winding roller
• Tensioning can pull out web bagginess. Every web has some amount of
cross web length variations.
• Accurate control of tensioning combined with speed control, sets the web's
mass flow rate.

Metal foil in R2R machine “Stripe coating” Web rewinder


Presentation
overview

Slot die coating



 A coating liquid is forced out from a
Slot die coating reservoir through a slot die by pressure,
and transferred to a moving web.
 The fluid dynamics inside the slot die
distribute the flow of the coating material
homogeneous over the full width of the
slot.
 The wet layer thickness on the web is
solely depending on the material flow,
the width of the slot and the speed of the
web. Independent of material viscosity or
surface tension.

Schematic view of slot die coater

Slot die coater with vacuum box



Slot die coating

Geometric parameters
 Design variables of the coating die: shape, position, die lips, feed slot,
web, gap clearance, radius of application roll
 Design variables define shape of slot die
Operating parameters
 Web speed
 Wet film thickness
 External forces e.g. gravity
electric or magnetic fields
 Gas pressure at upstream
and downstream menisci

Important parameters in slot coating flow experiment. L: lip
length, H: coating gap, W: slot gap, θs1: static contact angle,
θs2: separation angle, θd: dynamic contact angle.



Slot die coating – geometric parameters

Because of Ohms Law the functional layers should be:
• Extreme homogeneous in thickness!

Slot die coater with vacuum box



Slot die coating – fluid and material properties

Fluid and material properties
 The wetting behavior of the coating
fluid on the web and the coating die.
 The rheological properties of the
coating fluid
 The surface tension
 The density
 Properties of substrate

Inhomogeneous coating because of
wetting problems!



Slot die – OPV module
OPV Module
• To obtain sufficient voltage the individual cells
are serie connected in a solar module.
• The surface area ratio active zone/inactive
zone gives the module efficiency

Flexible OPV module

 Cross section of the layer structure of an OPV module
Vtot ≈ 3xVcel

Active zone Inactieve zone
-OPV cell- serie connection



Slot die - OPV module
 Multiple-pass thin film slot die coating for stacking functional layers
 Stripe coating a.k.a. R2R homogeneous patterning of thin film coating in
machine direction
 Accurate 2mm shifted thin layer stack
 Up to 5 layers

Slot die with shims for stripe Flexible OPV module
coating



Slot die - OPV module

The surface tension at
the edges of a stripe
could differ a lot.
Dewetting, coffee stain
effects and rough edges
could occur!

Overview of surface tension at layer edges

Wetting envelope for coating material to predict wettability


Presentation
overview

Contamination Control


© Holst Centre 32
  32

Particle defects in OLEDs.

Particle contamination during production causes fast degradation of OLEDS.

The contamination control should be an integral part of OLED
production.

Defects in OLED:
1. Fast growing in time: Barrier defect
2. Non growing: defect in active structure, covered by bulk cathode
3. Slow growing: defects in cathode covered by barrier

4 Barrier
Cathode 3 1
Light Emitting Layer 2
Anode
Schematic of some of the many particle defect that
could occur.




© Holst Centre
 34

Toolbox for measuring particles

Particle card Particle roller Particle (SEM) probe Particle fall out box

Technique lower detection lower detection large area SEM Remark
limit size sampling possible
#/cm2 micron (> 100 cm2)
Particle card 0,5 2--3 no yes general use
Particle roller < 0,1 2--3 yes yes large area sampling
Particle probe 0,5 0,3 no yes identification on shape, size ..
Particle fall out box 0,01/(hour) 2--3 -- yes finding local sources

Q3-2012-SIF-TP1

Presentation
overview

Summery



Summery

• There is a huge market for OLED for lighting if prices are made competitive
• OPV high potential if cell efficiencies go up or scares metals are unavailable
• R2R production is necessary for a competitive price
• The main challenge is to get a high production yield with many complex
production steps
• Functional layer homogeneity is very imported and difficult to obtain
• In-line OPV module production is easy to produce with slot die coating
• Contamination control should be integrated part of the production process


Presentation
overview

Holst Centre – Large Area Printing



Holst Centre Large Area Printing & Coating Program
The general goal of the Technical Program Large Area Printing, is to develop wet
deposition process technologies for R2R compatible application of patterned thin
and homogeneous layers of electro-active materials on flexible supports.

The electro-active materials currently envisaged in large area coating are mainly
used in OLED devices for lighting and signage and OPV modules.

The approach of large area coating program is generic, meaning that for possible
future new materials and applications, the technologies currently studied should
be (easily) adaptable to serve these new applications as well.

Some of the many prototypes made at the HOLST CENTRE.


Thank you for
your attention!
Visit us at
www.holstcentre.com

Arjan Langen - TNO/Holst Centre

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