HIL development opportunities

Towards more robust solutions

DOE SSL R&D Workshop Floryan De Campo Marc Sims

January 28th, 2015 Research & Innovation Solvay OLED

INTRODUCTION Each layer counts for performance AND cost

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Cathode EIL ETL EML HTL HIL

Anode

OLE

D S

TAC

K

EML layer is the “heart” or “engine” of OLED It must be carefully designed & optimized to achieve both high performance and long lifetime

However, an OLED like any other device is only as good as its “weakest link”

Can HIL be overlooked ?

INTRODUCTION Solution processed HIL economical value

“The biggest challenge for OLEDs is to develop acceptable, cost-effective manufacturing processes…”

“Since the performance of wet-processed emitters is still lagging, short-term interest is in the use of coating processes for the anode structures, hole injection layer (HIL), and hole transport layer (HTL). This offers significant cost savings through the elimination of the lithography steps and subsequent higher utilization of the conducting materials.”

Source: Manufacturing Roadmap, Solid-State Lighting Research and Development, U.S. Department of Energy, August 2014

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Role & Benefits of HILs Important to optimize and control

Role of HIL in OLED device Expected benefits of HIL • Lower operating voltage • Improved lifetime • Micro-cavity tuning • Improved efficiency • Planarization of electrode • Improved manufacturing yield

Materials stability and robustness must improve

Are there any other key properties to optimize in HIL ?

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STABILITY

Stability of HILs Intrinsic weaknesses of PEDOT:PSS and PANI ?

PEDOT:PSS and PANI are often cited as reference HILs for OLED • Probably the most studied materials in OLED as HILs • Claimed excellent stability, good work function • Can provide good planarization effect, good efficiency and lifetime

Limitations of PEDOT:PSS Limitations of PANI • Limited electron & UV stability (ref. 1) • Limited thermal stability (170 °C) (ref. 3) • Electrochemical de-doping under high • Large influence of counter anion

Ref .1: J. Polym. Sci. B: Polym. Phys. 2003, 41, 2561Solvay OLED Ref. 2: Peter K-H Ho et al., Adv. Mater. 2007, 19, 4202–4207

January 2015 Ref. 3: Polymer Degradation and Stability, 2004, 86, 187-195

electric field (> 20 kV.cm-1) (ref. 2)

Ageing at 173 °C

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Stability of HIL – Matrix effect Electron and thermal stability

Strong effect of matrix material (PHOST) on stability • More stable at high electric fields (up to 80-120 KV.cm-1) • Better thermal stability (no SO3 losses up to 200 °C) • Better efficiency and lifetime than PEDOT:PSS

S-P3MEET loses 50−60% of its -SO3 groups after being heated to 200 °C, but S­

P3MEET:PHOST does not lose -SO3 groups

Proposed explanations • Increased stability due to interaction with matrix • Blend is less sensitive to water uptake

Solvay OLED Peter K-H Ho et al., Chem. Mater. 2014, 26, 4724−4730 F. So et al. / Organic Electronics 15 (2014) 2513–2517 January 2015

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Tg 170°C 190°C 225°C

Thermal Device Stability vs. MatrixVoltage vs. Annealing Temperature

Additives or matrix materials can significantly improve device stability

150ºC

/ 15m

in

150ºC

/ 30min

150ºC

/ 60m

in

175ºC

/ 15m

in

175ºC

/ 30m

in

175ºC

/ 60min

190ºC

/ 15m

in

200ºC

/ 30m

in

200ºC

/ 60m

in

220ºC

/ 15 min

2 3 4 5 6 7 8 9

10

Vol

tage

@ 1

0mA

/cm

2

HIL Annealing Temperature

Formulation 1 Formulation 2

Al

NPB (vapor)

HIL (sol’n)

ITO

Glass Matr

ix 1

Matrix

2

Matrix

3

100

150

200

250

Cut

off

Ann

eal T

empe

ratu

reCut-off temperature determined based on hole-injection into NPB (i.e., Voltage at 10 mA/cm2 <2.5 V)

Effect of matrix or additives Internal results on thermal stability

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INTERFACE

Formulation of PEDOT:PSS Effect of PFI (perfluorinated ionomer)

Simple formulation of PEDOT:PSS with PFI enhances performance • Deeper work function (as high as 5.95 eV) • Increased luminous efficiency and lifetime • HIL could replace HIL + HTL layer

green-light-emitting device (polyfluorene derivative (LUMATION 1300 series Green Polymer))

Three main effects claimed due to self-organization of PFI at interface • Better hole injection (deeper work function) • Efficient electron blocking • Efficient prevention of exciton quenching (at HIL/LEP interface)

Solvay OLED T-W Lee et al., Adv. Funct. Mater. 2007, 17, 390–396

January 2015 T-W Lee et al., Adv. Mater. 2012, 24, 1487–1493 10

Formulation of PANI-PSS Effect of PFI (perfluorinated ionomer)

Simple formulation of PANI:PSS with PFI enhances performance • Deeper work function (as high as 6.09 eV) • Increased luminous efficiency and lifetime

ITO/HIL/NPB/Bebq2:C545T/Bebq2/Liq/Al

Similar effect as with PEDOT:PSS at interface ? • Claim increased doping stability • Blocking diffusion due to PFI at interface

Solvay OLED T-W Lee et al., Angew. Chem. Int. Ed. 2011, 50, 6274 –6277 January 2015

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Polythienothiophene (PTT) with PFI Improved stability vs. PEDOT:PSS

PTT with PFI (aka. PFFSA) has a better performance than PEDOT:PSS • Deeper work function (as high as 5.6 eV) • Increased luminous efficiency and lifetime

Proposed mechanism for OLED degradation without HIL • Charge accumulation at anode / HTL interface • Good HIL prevents accumulation and improves stability

Solvay OLED F. So et al. / Organic Electronics 14 (2013) 2518–2522 January 2015

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SOLVENTS

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Improved lifetime consistently observed with non-aqueous HIL

Aqueous vs. Non Aqueous Is water detrimental to lifetime ?

0 1000 2000 3000 4000 15

20

25

30

35

AQ1200 NQ1

NQ2Pow

er e

ffica

cy (l

m/W

)

LT50 from 1000 cd/m2 (h)

ITO / Glass

AQ1200 or NQ1 or NQ2

Al

XET010

NPD Blue EML

XEI013:Dopant

0 5000 10000 15000 20000 25000 35

36

37

38

39

40

AQ1200

NQ1

HAT-CN

Pow

er e

ffica

cy (l

m/W

)LT50 from 1000 cd/m2 (h)

ITO / Glass

AQ1200, HAT-CN or NQ1

Ag

XET010

XT314 White EML

XEI013:Dopant

Blue PhOLED White PhOLED

What is the contribution of improved hole injection vs. the presence of water ?

Aqueous

Non-aqueous Non-aqueousAqueous

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INTRACTABILITY

Intractability – Beyond thickness control Diffusion of harmful species

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• Time resolved PL as an intractability probe

• HIL impurities can migrate into HTL

• Impurity species create polarons in HTL

• Exciton-polaron quenching

Transient PL profiles

Devt HIL

glass

AQ1200

PL Lifetime vs. HIL

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What is the extent of HTL impurity doping with NQ1?

12nm150nm

Intractability – Beyond thickness control Diffusion of harmful species

C = Cgeom + Ctraps C = CSchottky + Ctraps

HIL (AQ1200)

HTL HTL+ +

++ + +

+

+ +

+ + +

+ ++

+ +

+

+ + + ++

HIL (NQ1)

CV analysis • Doping profile extends throughout 150nm HTL

• Diffusion of impurities deep into HTL

• Schottky barrier with 12nm depletion region at Al | HTL interface

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FORMULATION

Concentration (%TS) Viscosity Rheology Surface Tension Acidity Boiling point Toxicity Shelf Life Etc.In

k C

hara

cter

istic

s Planarization Intractability Work function Resistivity Transparency Surface energy Uniformity Roughness Etc.Fi

lm C

hara

cter

istic

s

Solu

tion

Proc

ess

Dev

ice

Perf

orm

ance

Ink characteristics must be matched to coating equipment requirements to deliver high-quality thin films that result in high-performance OLED devices

Slot Die Coating Ink Jet Printing

Formulation Essential to Drive Performance

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Formulation is critical (ink stability & film control)

Conclusions & Perspectives Towards the development of more robust HILs

HIL have some strong benefits Key parameters for good HILs • Some efficiency improvement • Thermal stability • Significant lifetime improvement • Interface control • Could lower cost • Water free ?

• Full intractability

Reported strategies to improve HIL • Formulation with matrices • Formulation with ionomers (interface) • Switch from aqueous to non-aqueous systems

Our current focus for new HILs generations • Solvent based HILs • High thermal stability (> 250 °C) • Full intractability • Robust to formulate (ink stability & film control)

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Thank you!

Solar Impulse – Solvay’s “Flying Lab”

Contacts: • Bill Chen (General Manager) / Seoul – bill.chen@solvay.com • Floryan De Campo (Head of Technology) / Pittsburgh– floryan.decampo@solvay.com

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Solvay OLED An Internal Start-up

Solvay OLED is an incubator (internal startup) part of Corp R&I, Emerging Business (Corporate Ventures)

Global Chemical Company - Stable financial investment - Strong process engineering - Strong corporate services

Start-up - Entrepreneurship, risk taking - Innovative materials - Sharp new business focus

Combining the best of both worlds

Our Target – transform into a business in 3-5 years focusing on Display & Lighting markets

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Solvay OLED - Capabilities INNOVATION - RELIABILITY ­ CUSTOMER FOCUS

2 Centers

Pittsburgh, USA Seoul, S. Korea

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Solvay OLED – HIL Solutions Polythiophene platform provides

three tunable levers to customize key properties of HIL

Conductive Polymers

Doping Systems

Formulation

Fine tuning of molecular design • Library of monomers • Polymers & co-polymers

Adjusting key properties • Self-doped • Proprietary dopants

Optimizing inks • Polymeric matrix • Solvents & additives

Unique HIL Platform

Properties Aqueous Solvent based Work function Hole injection Resistivity Transparency Intractability Viscosity Surface energy Wettability Stability Etc.

S n

R1 R2

X Y

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Solvay OLED

HIL HTL Host Polythiophene Platform

• Unique and tunable • Molecular design • Doping systems • Formulation

• Customizing solution HIL • Work function • Hole injection • Resistivity • Etc.

VTE Technologies

Solution Technologies

VTE Technologies

Solution Technologies

• High triplet cores • Molecular design • Proprietary systems • Scaled up chemistries

• Customized structures • Molecular design • Proprietary systems • Scaled up chemistries

• Intractability solutions • X-linking systems • Orthogonal solvents • New concepts

• Cores alterations • Soluble groups introduction • VTE vs. solution

Providing Solutions from Anode to EML

S n

R1 R2

X Y

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