Soft x-ray nanoanalytical tools for thin film organic electronics

Soft x-ray nanoanalytical tools for thin film organic electronics

Rainer H. Fink

Friedrich-Alexander University Erlangen-NürnbergPhysical Chemistry 2 (surface & interface science)

http://www.raifi.de

莱纳 · 芬克教授 博士

Chemistry @ FAU: Excellence in research

• Funding: 2013: More than 8.6 million € p.a. third-party funds

2010 – 2012: On average 7.3 € p.a. third-party funds

• DFG Funding Atlas 2012: Number 2 in Germany in DFG based funding

• Taiwan Ranking 2014: World rank: 70

(since 2009: >1,350 papers, 142 JACS or Angew.Ch. and 16 Science or Nature)

• Shanghai Academic Ranking of World Universities 2014: TOP 75, #1 in FAU

FAU relationship to ACES / UoW

• International student exchange programs (since 2006)

• Double degree programs: M.Sc. „Chemistry – in International Degree“

• Joint PhD program

• D. Guldi – Co-PI at ACES (dye-sensitized solar cells)

Synthetic Carbon AllotropesOrganic Nanostructures, molecular wires

Supramolecular Chemistry

Time-resolved charge transfer

Photovoltaics / artificial leaves / energy

From molecules to materials & devices

Our department focuses on ...

Research focus of the Fink group

Organic molecules,Organic thin films

Polymer films, nanostructures

Organic electronic devices

Instrumentation for x-ray based

microspectroscopy

„ferric wheels“, molecular magnets

Hybrid partices

Includes development of novel soft x-ray instrumentation

In-operando study of OFETs (30 nm pentacene)

Channel length: 250 μmChannel width: 20/40 μm

Device characteristics comparableto „conventional“ devices

-10 -5 0 50,0

5,0x10-4

1,0x10-3

1,5x10-3

2,0x10-3

2,5x10-3 Drain-source voltage = -10 V

Gate-source voltage (V)

Sq

uare

ro

ot

of

dra

in c

urr

en

t [

mA

]

10-12

10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

Dra

in c

urr

en

t (A

)

Transfer characteristics:field effect mobility (RT): μ = 0.6 cm²/Vs

Ion / IOff ratio: 5 x 106

threshold voltage: Vth = -2.3 V

subthreshold slope: S ≈ 0.3 V/dec

VLM

Contrast in soft x-ray microspectroscopy

Chemical speciation through X-ray absorption spectra (NEXAFS)

C, N, O K-edges

[µm

]

Specimen thickness: 2 - 200 nm

Chemical fingerprint &

electronic structure

Scanning transmission x-ray microspectroscopy (PolLux-STXM)

J. Raabe et al., Rev. Sci. Instrum. 79 (2008) 113704

Inside the PolLux-STXM

Resolution outermost zone width

Proven resolution: 12 nm

(< 10 nm in progress)

Film morphology/molecular orientation - DHDAP

STXM FOV 20 x 20 mm2

AFM 5 x 5 mm2

On Si3N4On Al/Al2O3

reso

nan

t3

10 e

V

STXM / NEXAFS

1 µm

X-ray polarization

C 1s π* resonance at 283.3 eV

In-situ study of pentacene-based OFET – 5 nm

Calculations: B. Paez-Sierra,Ph.D. thesis

Experiments:C. Hub et al., J. Mat.Chem. 20 (2010) 4884

282 284 286 288 290

UG: 0V / U

D: 0V

inte

nsity [a.u

.]

UG: -10V / U

D: -10V

absorption electron yield

Diacetamide-4-thiophenes

AFM 15 x 15 mm2

STXM 14 x 14 mm2 STXM 6 x 6mm2

Strongly anisotropic growth due to

pp-interaction & H-bonding

Rainer Fink, March 14, 2015 (SUSTC Shenzhen)

OFET studies

3 nm Ac4T (p-type)

within active channel

hv = 287,5 eV

12 x 12 µm2

gate effect: yestransport effect: no !

Number of charge carriers is too low

(injection limited !)

Charge trapping ?

SAMFETs

All functionalities in one molecule

M. Halik and A. Hirsch, Adv. Mater. 23 (2011) 2689

(ongoing STXM study)

Charge trapping in pentacene films – Raman Microscopy

B. Rösner et al. Organ. Electronics (2014)

M. Tello, H. Sirringhaus, Adv. Funct. Mater. 2008

charge trapping in intergrain regions

reaction in solution reaction in the gas phase

5 µm

SEM

1 µm

SEM

1 µm

SEM

clo

sed

silv

er f

ilm

clo

sed

silv

er f

ilm

80° sample tilt

Ag (30 nm)

Si substrate

p = 10-2 mbarT = 90°-150°CAg (30 nm)

saturated TCNQ solution

Si substrate

in acetonitrile saturated TCNQ vapour phase

Ag-TCNQ CT-complexes

Electronically bistable Electrocatalytically activePhotoactivity

Distinguish neutral and charged species spectroscopically

Confocal Raman Microscopy Micro-NEXAFS

Quantitative evaluation

of affected molecules

B. Rösner et al., PCCP (submitted)

Solar cell device performance

PC60BM +DIO +DIO+Eva

STXM micrographs recorded at 284.5 eV (5 × 5 µm2)

PDPP-TT+PC60BM

Bulk heterojunction solar cells (DIO optimizes nanomorphology)

RSoXS applied to binary/ternary polymer solar cells

ICBA Si-PCDBTBT

283 284 285 286 287 288 289 290 291 292 293 294 295

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

P3HT ICBA Si-PCPDTBT

Lin

ner

Abso

rptio

n (

nm

-1)

Photon Energy (eV)

P3HT

STXM 284.5 eV

STXM cannot resolve

the nanostructure !

10-8

10-7

10-6

Co

ntra

st (

)

290285280275270

Energy [eV]

Orientation Density

Contrast Functions

Inte

nsity

[au]

4 5 60.01

2 3 4 5 60.1

2 3 4

q [nm-1

]

1000 100 202/q [nm]

270 eV

P-SoXS Profiles

Inte

nsity

[au]

4 5 60.01

2 3 4 5 60.1

2 3 4

q [nm-1

]

1000 100 202/q [nm]

270 eV 284.2 285.9 289

● Large, well-defined domains● Easily identified via microscopy

● P-SoXS also separates mass-contrast & orientation through contrast functions

2μm2μm

Non-resonant Resonant

STXM

Mass-Thickness Contrast Dominates

Orientational ContrastDominates

Individual DomainsOrientational Domain Clusters

Feature Position = Size

Feature Intensity = Level of ordering

P-SoXS Demonstration: Pentacene

Ternary polymer solar cells

X. Du et al, Macromolec. Lett. (submitted)

Azimuthally integrated scattering profiles with associated peak fits and

calculation of the Total Scattered Intensity (TSI) for P3HT: Si-PCPDTBT: ICBA

blends

SiZZ

0.2

SiZZ

0.35 SiZZ

0.5

Nanostructure correlates with optimum device performance

Summary & conclusions

●STXMs offer superb resolution based on recent zone plate developments

●NEXAFS detects modifications in the unoccupied DOS in OFETs under operation – still some issues with potential energy shifts (p-materials ?)

●Combine STXM with complementary microscopies to access interesting material properties (especially in-situ microspectroscopy)

●RSoXS complements STXM for structures below the ZP resolution limit

●NanoXAS: combine STXM and AFM at same spot

x-rays

z

Cantilever