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Pathway to Low Cost Electrodes 1 Printed Electrodes for OLED Panels January 30 th , DOE SSL R&D workshop Hongmei Zhang

Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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Page 1: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

Pathway to Low Cost Electrodes

1

Printed Electrodes for OLED Panels

January 30th, DOE SSL R&D workshop

Hongmei Zhang

Page 2: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

2

• Overview of current OLED fabrication process-critical area for cost reduction

• How solution process can lead to reduction in

Photolithography processes • Material and process technique requirement for printing

anodes • Summary and conclusion

Outline

Page 3: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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Hurdle to OLED Lighting Adoption

Page 4: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

4

Implication of Cost Reduction Plan from a OLED panel Manufacturer

• Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8.

• All photolithography processes are in anode structure fabrication

• Direct patterning process technology are needed

* From LG Chem presentation at 2012 OLED summit in San Francisco

HIL

Anode

EML

ETL

Cathode

HTL

Page 5: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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Current Anode fabrication Process

5

TC and Metal Contacts(without metal grids) Process

Substrate cleaning

Sputtered ITO

7 step process ($$$$) to obtain anode structure

Photolith Etch Metal Film Deposition

Photolith Etch to

form contacts

If Metal Grids are required

Insulator coating

HIL Film Formation

3 extra process steps are added to insulate metal grids

Photolith etch Substrate Cleaning

Total of 10 process steps are required to form anode structure, 6 of which are photolithography steps.

Page 6: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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• Slot-die coated HIL can potentially eliminated the need for insulator

• Increase thru-put (removed 3 process steps) • Reduction in material cost

Thick Solution Processed HIL Reduces Photolithography Steps

Glass Substrate

Metal Insulator is required in vapor HIL to prevent shorts

Vapor HIL

ITO

Glass Substrate

Metal Solution HIL

ITO

Standard Process

• Metal grids are necessary for panel (uniformity and power efficiency) since best TC > 5 Ω / sq

• Serial connections require even more organic layer patterning steps

Page 7: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

7

Further Reduction in Photolithography Processes Demands All Solution Processed Anode Structure

ITO still requires patterning

Glass

ITO

Vapor HIL Sputtered/patterned Metal Grids

Glass

Printed HIL ILE

Current Approach

Future Trend

Printed Grids All solution Processed Anode structure will eliminate the need for lithography and etch

Glass ITO

Print HIL Printed Grids

Current OLED Lighting panel manufacture are using ITO, some do not use metal grids

Page 8: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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Grids Requirement and Material Options Grids Requirment: •Sheet resistance < 1 Ohm/sq •>90% optical transparency •< 1 um is prefered •<150 um line width

High Conductivity Metals: •Ag is currently the material of choice for printing, other high conductivity metals such as Cu and Al are challenging for solution process due to oxidation issue. Au is too expensive

Page 9: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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Ag Ink and Printing Techniques

Printing Technique PROS CONS

Ink Jet Printing • High resolution • Good thickness control

• Multi-pass for thicker films • Lower throughput • Yield issue

Screen printing • High throughput • Mature technology •Simple tooling

• Lower resolution • Poor thickness control

Ag ink Options: • Current commercial available IJP or screen printable Ag inks are nanoparticle

based with typical resistivity value around 5 -10x bulk Ag • Thick grids are needed in order to achieve low sheet resistance while maintain

optical transparency. This post challenges for planarization. Example: with 5% area coverage and ρ = 5 * ρ (Ag bulk), the needed line thickness is 3.2 μm for 1 Ω / sq )

• New metal ink technology with resistivity close to Bulk Ag will enable thinner grid lines

Page 10: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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Requirement for HIL as Current Spread Media

Anode type Thickness * (µm)

Grid spacing (cm)

Rs (Ω/sq)

HIL resistivity (ohm-cm)

IJP Ag Grids + HIL 0.2-1 0.15-0.5 1-10 < 0.03

Integration of metal grids with HIL: • HIL wth high Conductivity

and high optical transparency • Compatible solvent with Ag

to prevent potential metal migration issues

Ag inks ρ <5µΩ-cm, grid area <10%, pixel uniformity >90%, line width~75-150 um

Page 11: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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Printed Metal Grids / Printed HIL Process

Roadmap for Low Cost Electrodes

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Current Metal Grids or Bus Bar / Vapor HIL Process Tri layer

metal deposition

Evaporate HIL film

7 step process ($$$$) to obtain substrate with Electrodes

Photolith

Etching to form metal grids

Insulator coating

Photolith Substrate Cleaning

Metal Grid / Printed (Thick) HIL Process Tri layer

metal deposition

Slot-die coating HIL

5 step process ($$$) to obtain substrate with Electrodes

Photolith

Etching to form metal grids

Insulator coating

Photolith Substrate Cleaning

Print Metal Grids

Slot-die Coating Photolith

Etching to form metal grids

Insulator coating

Photolith Substrate Cleaning

3 step process ($$) to obtain substrates with Electrodes

Page 12: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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Large Area OLED Panel on Printed Grids

• Large area single ‘pixel’ OLED made with HIL slot die coated on top of ink jet printed Ag grids on ITO electrode.

• No insulation layer on grids • No shorts observed

Page 13: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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OLED Test Device Made with HIL + Printed Metal Grids as Transparent Conductor

200nm HIL

HIL

Ag

• OLED device fabricated on Slot-die coated HIL on Ag metal grids as transparent conductor are shown above with varying HIL sheet resistance

• Solution HIL is used as both a Hole Injection layer as well as current spread media

Higher Sheet Resistance HIL Lower Sheet Resistance HIL HIL Planarize printed Ag metal grids

Page 14: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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Conclusion

• Research and Development effort in new anode material and process integration are needed for low cost electrodes.

• Material and process development should keep panel

manufacturing process flow in mind while developing new technology

• Cost reduction in OLED lighting manufacturing can not

simply rely on volume production and scale up. Material, process and equipment development will need to work together.

Page 15: Printed Electrodes for OLED Panels · 2016-09-20 · • Target for cost reduction in Photolithography process is from 100% today down to 3% by Gen8. • All photolithography processes

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OLED Adoption Pathway

OLED Display manufacture believes that VTE manufacturing process will not enable the price point for mass market adoption of large area TV. Beyond Gen5, printing process is necessary. This can pave the path for OLED lighting