This document discusses the use of soft x-ray nanoanalytical tools for studying thin film organic electronics. Specifically, it summarizes research using scanning transmission x-ray microspectroscopy (STXM) and resonant soft x-ray scattering (RSoXS) to characterize the nanoscale morphology, chemical composition, and charge transport properties of organic thin films and devices. STXM provides chemical imaging down to 12 nm resolution while RSoXS can resolve structures below the STXM resolution limit. Together these techniques provide insights into structure-property relationships in organic photovoltaics, field-effect transistors, and other organic electronic materials and devices.

1. Soft x-ray nanoanalytical tools for
thin film organic electronics
Rainer H. Fink
Friedrich-Alexander University Erlangen-Nürnberg
Physical Chemistry 2 (surface & interface science)
http://www.raifi.de
莱纳·芬克教授 博士

2. 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)

3. Synthetic Carbon Allotropes
Organic Nanostructures, molecular wires
Supramolecular
Chemistry
Time-resolved
charge transfer
Photovoltaics /
artificial leaves /
energy
From molecules to
materials & devices
Our department focuses on ...

4. 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

5. In-operando study of OFETs (30 nm pentacene)
Channel length: 250 μm
Channel width: 20/40 μm
Device characteristics comparable
to „conventional“ devices
-10 -5 0 5
0,0
5,0x10
-4
1,0x10
-3
1,5x10
-3
2,0x10
-3
2,5x10
-3 Drain-source voltage = -10 V
Gate-source voltage (V)
Squarerootofdraincurrent[mA]
10
-12
10
-11
1x10
-10
1x10
-9
1x10
-8
1x10
-7
1x10
-6
1x10
-5
Draincurrent(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

6. 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

7. 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)

8. Film morphology/molecular orientation - DHDAP
STXM FOV 20 x 20 mm2
AFM 5 x 5 mm2
On Si3N4
On Al/Al2O3
resonant310eV

9. STXM / NEXAFS
1 µm
X-ray
polarization
C 1s  π* resonance at 283.3 eV

10. 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 / UD
: 0V
intensity[a.u.]
UG
: -10V / UD
: -10Vabsorption electron yield

11. 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)

12. OFET studies
3 nm Ac4T (p-type)
within active channel
hv = 287,5 eV
12 x 12 µm2
gate effect: yes
transport 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)

13. 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

14. reaction in solution reaction in the gas phase
5 µm
SEM
1 µm
SEM
1 µm
SEM
closedsilverfilm
closedsilverfilm
80° sample tilt
Ag (30 nm)
Si substrate
p = 10-2 mbar
T = 90°-150°CAg (30 nm)
saturated TCNQ solution
Si substrate
in acetonitrile saturated TCNQ vapour phase
Ag-TCNQ CT-complexes
Electronically bistable
Electrocatalytically active
Photoactivity

15. Distinguish neutral and charged species spectroscopically
Confocal Raman Microscopy Micro-NEXAFS
Quantitative evaluation
of affected molecules
B. Rösner et al., PCCP (submitted)

16. 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)

17. 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
LinnerAbsorption(nm-1
)
Photon Energy (eV)
P3HT
STXM 284.5 eV
STXM cannot resolve
the nanostructure !

18. 10
-8
10
-7
10
-6
Contrast(



)
290285280275270
Energy [eV]
Orientation
Density
Contrast Functions
Intensity[au]
4 5 6
0.01
2 3 4 5 6
0.1
2 3 4
q [nm
-1
]
1000 100 202p/q [nm]
270 eV
P-SoXS Profiles
Intensity[au]
4 5 6
0.01
2 3 4 5 6
0.1
2 3 4
q [nm
-1
]
1000 100 202p/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
46
2μm
58
2μm
Non-resonant Resonant
STXM
Mass-Thickness
Contrast Dominates
Orientational Contrast
Dominates
Individual DomainsOrientational
Domain Clusters
Feature Position
= Size
Feature Intensity
= Level of ordering
P-SoXS Demonstration: Pentacene

19. 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

20. 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
z
Cantilever