Dr. Maria Sramek, Siemens AG, Erlangen - Funktionelle Farbstoffe

Functional Dyes – Innovations in Medicine and Technology 

Functional Dyes for Organic 

Semiconductor Sensors 

Siemens AG 

Corporate Technology 

Erlangen, Germany 

Dr. Maria Sramek, Dr. Oliver Hayden, Sandro Tedde, Tobias Rauch 

Siemens AG, Corporate Technology CT T DE HW 3 

Global Technology Field „Organic Electronics“ 

Günther-Scharowsky-Straße 1, D-91050 Erlangen 

Phone: +49 9131 7 32443 

Email: maria.sramek@siemens.com 

Web: http://www.siemens.com/corporate-technology 

Page 1 May 2012 Dr. M. Sramek 

Copyright © Siemens AG 2012. All rights reserved. 

CT T DE HW 3/ Erlangen Süd

Motivation 

R&D Program „System Solutions“ 

Organic 

semiconductor 

Nanorods 

Quantum dots 

nanocrystals 

Fullerenes 

„Working Nanotechnology“ 

From Materials to Business Concepts 

Carbon 

nanotubes 

X-ray imaging Industrial sensors In-vitro diagnostics Open innovation 




Outline 

1. Introduction 

2. Processing 

3. Applications for Visible and Infrared Range 




Outline 


1.a - Review 

1.b - Organic Photodiodes 

2. Processing 





„Silicon is Gods Material“ and What About Organics? 

Crystalline and impurityfree 

substrates 

12‘‘/30 cm 

Workhorse - wafer 

Aim: Integration to cut costs (CMOS paradigm) 

Organic electronics – which way to go: 

- Low-cost processing vs. efficiency 

- Performance vs. material costs/purity 

- Large footprint vs. integrated solutions 

- Lifetime vs. Flexibility 

- Premium vs. low-cost products 



CT T DE HW 3/ Erlangen Süd 

Molecules/Polymers 

Roll-to-roll

„Nobel History“ of Conductive Organics 

1996 

2000 

Fullerenes („Buckyballs“) Conductive Polymers 

„Replace silicon“ and „organics beyond silicon bandgap limit“ 




Properties of Small Molecules & Polymers 

Small molecules 

Amorphous to highly crystalline, designed for the target application OLED - OFET 

High mobility possible 

Cheap purification (sublimation, re-crystallization) 

Ready for deposition – minor batch dependence 

Vacuum deposition 

Polymers 

Amorphous to crystalline domains, designed for the target application (any) 

Low to medium mobility 

Expensive purification (chromatography, re-precipitation) 

Most are only soluble in chlorinated & aromatic solvents 

Specific deposition formulation necessary – major batch dependence 

Solution deposition (no vacuum deposition processes) 

The performance requirements of the application influences 

the choice of materials and the setup of equipment 




Device Fabrication 

Silicon Organics 




Revolution to Evolution 

Example of OLED Display Developments 

Uni Bayreuth 

1994 

Philips, Passiv Matrix 

1999 

Sanyo-Kodak 2000 

Sony 11-inch OLED 

2008 

BenQ/Siemens 

Activ Matrix 2006 




Samsung 2009 

Mitsubishi 155-inch OLED 

2009 

The Holy Grail – Flexible TV

Pros and Cons 

Pros: 

Technology is compatible with Large area processes (low cost) 

Low temperature processing (low cost) 

Molecules and polymers can be tailored for specific electronic or optical 

properties 

Compatible with inorganic semiconductors 

Cons: 

Low carrier mobility 

Electronic and optical stability of the materials 

Processing is incompatible with classical processing in semiconductor 

industry 




Outline 


1.a - Review 

1.b - Organic Photodiodes 

2. Processing 





Organic Diode 

Solid state: PN-junction 

p-type n-type 

Depletion region 

Anode Cathode 

Organic: „Bulk heterojunction“ 




C - 

O 

OMe 

O 

OMe 

C 3- 

C 3- 

O 4+ 

O 

OMe 

C 4- 

C 3- 

O 

OMe 

C- 

- 

C 

Semiconducting polymer 

O 

OMe 

+ 

C - 

O 4+ 

C - 

O 

OMe 

C 3- 

O 

OMe 

O 

OMe 

C 2- 

C 2- 

C 2- 

O 

OMe 

Fullerene 

Anode Cathode 

Bulk heterojunction = blend of electron donor/acceptor (eg. polythiophene/fullerene) 

No distinct pn-junction as in solid-state devices 

High absorption coefficient of the semiconducting polymers (~10 5 cm -1 ) 

O 

OMe 

C - 

C - 

C 3- 

O 

OMe 

C 2- 

C - 

O 

OMe

Layer Stack of Organic Photodiodes (OPDs) 

ITO (Anode) 

Encapsulation 

Cathode 

Bulk heterojunction (P3HT/PCBM/quantum dots) 

Interlayer 

Substrate 

ITO (Anode) 




EQE (normalized) 

VIS to NIR Spectral Sensitivity 

1,0 

0,8 

0,6 

0,4 

0,2 

0,0 

Standard P3HT/PCBM 

(cf. plastic solar cells) 

400 500 600 700 800 900 1000 

Wavelength (nm) 

Low bandgap absorber 

Organic absorber up to ~1 µm 

Inorganic absorber >1 µm 

400 500 600 700 800 900 1000 1100 




EQE (%) 

80 

70 

60 

50 

40 

30 

20 

10 

0 

-10 

Wavelength (nm)

Current Density (mA/cm²) 

Current/Voltage Characteristics 

10 1 

10 0 

10 -1 

10 -2 

10 -3 

10 -4 

10 -5 

10 -6 

10 -7 

10 -8 

10 -9 

Reverse bias 

AM 1.5 (solar) 

532 nm @ 780 µW/cm 2 

Dark current 

-5 -4 -3 -2 -1 0 1 2 

Voltage (V) 

OPD active area 

1 cm² 

Statistics over 100 devices 

Forward bias 

5V.light 1V.light 




Current density (mA/cm 2 ) 

Current density (mA/cm 2 ) 

1x10 -4 

1x10 -4 

8x10 -5 

6x10 -5 

4x10 -5 

2x10 -5 

0,35 

0,30 

0,25 

0,20 

0,15 

0 

Dark currents 

5V.dark 1V.dark 

Photocurrents

Outline 


2. Processing 





Coating Techniques Comparison: 

Spin coating / Doctor blading / Spray coating 

Spin coating 

Doctor blading 

Spray coating 

PEDOT:PSS 




Spray Coating as Fabrication Process for OPDs 

OPD fabrication with spray coating 

in ambient conditions: 

Substrate independence 

Adjustable layer thickness 

Multiple spray-coated layers 

Flexibility using solvents 

Layer roughness is not a limitation 

Low/high throughput technique 

Scalable technology 

Movie „Spray coating of OPDs“ 

S. Tedde et al., Fully Spray Coated Organic Photodiodes, 

Nano Letters 9 (3), 980 (2009) 




Outline 


2. Processing 





Application in the Visible Range: 

Organic Matrix X-Ray Detector 

X-Ray image of 

hand phantom: 

Backplane 

Pixels 

Processed panel 




Application in the NIR Range: 

Small Bandgap Polymer NIR OPDs 

– Fabrication Parameters 

Substrate size: 50x50 mm² 

Number of OPDs on each substrate: 16 

Single OPD active area : 71.4 mm² 

poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4- 

b]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] 

(PCPDTBT) 

Semiconductor: blend of PCBM / PCPDTBT 

PCPDTBT E g : 1.46 eV 

Easy and fast 

production processes 

Large area 

(cm² range) 

Thin 

(< 1mm) 

Acknowledgements: 

Semitransparent 




Dynamic Response and f -3dB 

Signal (20*log(U/U 0 )) [dB] 

0 

-2 

-4 

-6 

-8 

-10 

Active area: 0.7 cm 2 

Signal [dB] 

-3dB 

f -3bB = 130 KHz 

10 100 1k 10k 100k 

Frequency [Hz] 

Light source: - 1 KingBright SMD Chip LED KPL-3015SRC-PRV 

( peak ~660 nm) super bright red light 

- Light intensity ~ 130 µW/cm² 





Light Barrier with OPDs 

Motivation 

Specification 

Demonstrate potential of organic photodiodes 

for new multidimensional light barrier applications 

Show that OPDs can substitute „silicon“ @ NIR 

Optic-free light barrier for variable emitter/detector 

distance 

High flexibility with respect to active area (mm²-cm²) 

Quadrant functionality: 

- Self-alignment of emitter/detector 

- Determination of direction/angle, and speed 




Organic Quadrant Sensor (~4 cm² Active Area) 

Resolution Limit ~1 µm 

Distance (µm) 

1,0 

0,0 

-1,0 

-2,0 

-3,0 

-4,0 

-5,0 

-6,0 

-7,0 

1.5 µm steps @ 15° 

X-axis 

40 42 44 46 48 50 52 54 

Time (s) 

Y-axis 

4 organic photodiodes (A, B, C, D) giving X/Y positioning results for a light spot 

Absolute X/Y position is calculated according to formula 




X 

Y 

( B D) ( A C) 

 

A B C D 

( A B) ( C D) 

 

A B C D


PSD/Light Barrier @ 660 nm Demonstrator 

4 Quadrant OPD Light Barrier 

Conveyor belt Implementation 




NIR OPDs with a Small Molecule Absorber: 

Squaraine (SQ+PCBM = Polymer-Free BHJ) 

EQE [%] 

100 

80 

60 

40 

20 

External quantum efficiency IV-characteristic 

EQE 0 V 

- 1 V 

- 2 V 

- 3 V 

- 4 V 

- 5 V 

- 6 V 

- 7 V 

0 

400 600 800 1000 

Wavelength [nm] 

-5 -4 -3 -2 -1 0 1 2 

Voltage [V] 

NIR peak sensitivity ~800 nm (tunable); low absorption in visible spectrum 

Dynamic response: -3 dB @ ~150 kHz (~1 cm² active area) 

Synthesis yield >90% (effortless up-scaling) 

Key advantage: Low cost absorber; no extensive polymer purification needed 




Current Density [mA cm -2 ] 

10 2 

10 1 

10 0 

10 -1 

10 -2 

10 -3 

10 -4 

10 -5 

10 -6 

532 nm 

Solar 

870 nm 

Dark

Small Molecule Absorber Squaraine: 

Dynamic Response and f -3dB 

sprayed 

doctorbladed 

Signal (20*log(U/U 0 )) [dB] 

0 

-2 

-4 

-6 

Reverse bias: -2V applied 

OPD response 

f -3dB 

f -3dB = 100 KHz 

10 100 1k 10k 100k 1M 

Frequency [Hz] 




Application in the SWIR Range: 

Pushing The Limits of OPDs with Quantum Dots 

Visible Application: Photography 

Si Bandgap 

NIR Imaging (0.7-2.5 µm): 

- Active night vision systems 

(NIR source) 

- Security applications 

(machine vision) 

- Tomography 

(Tissue scanning) 

QD range 

MIR Imaging (3-5 µm): 

- Thermal Imaging 

- Passive night vision systems 

www.omega.com 




Hybrid Organic/Colloidal Photodiodes 

Schematic layout of an a-Si active matrix 

TFT panel with OPDs 

Photosensitive layer: 

Bulk heterojunction (P3HT:PCBM) 

with embedded PbS QD absorber 

Imager: 256x256 pixels 

with 154 µm pixel pitch 

T. Rauch et al., Near-infrared imaging with quantum 

dot sensitized organic photodiodes, Nature Photonics, 

3, 332-336 (2009) 




Tunable Spectral Response with High EQE 

EQE of an organic photodiode sensitized with 

PbS-QDs of 4.6 nm diameter 

Peak sensitivity at 1290 nm with 18.4% EQE 

Electrons 

EQE 

~ (%) 

Photon 

Tunable NIR sensitivity with increasing QD 

diameter 

Cut-off wavelength: 1350 nm to 1850 nm 




Current/Voltage Characteristic and Lifetime 

I-V characteristics 

High photoresponse for polychromatic light 

>870 nm 

Stable diode rectification ratio 

up to 8000 @ +/-2V 

Lifetime of more than one year! 

Accelerated lifetime conditions of 38°C and 

90% rel. Humidity 

Stability for both, dark and light currents 

in the visibile and NIR region 




Energy Band Diagram 

PbS 

Staggered band alignment between 

P3HT and the PbS QD 

Almost flat band condition between the LUMO 

of PCBM and energy level of the PbS QD 

(first excitonic transition) 

QD can act as sensitizer and as 

traps 

Conduction via QDs is unlikely due 

to long oleic acid ligands and the 

conductivity is orders of magnitudes 

lower compared to the bulkheterojunction 

material P3HT/PCBM 

No energy barrier for electron 

transfer between QD and PCBM; 

applied bias assists charge carrier 

transfer 

Hole transfer might be possible from 

QDs to P3HT and/or to PEDOT 




SWIR-Imaging 

Images @ 1310 nm Movies @ 1310 nm 

Shadow cast of a slide (flat fielding) 

Original slide showing a monarch butterlfly 

Si works only up to 1100 nm! 

256x256 a-Si AM TFT panel (154 µm pixel pitch) 

Video shows 2 woodlice (young woodlouse on 

the back/adult woodlouse cleans its antennae 

with a foreleg) 




Conclusion 

Motivation: 

Replace silicon @ NIR for large active areas 

Solution-processable semiconductors beyond silicon bandgap limit 

Industrial fabrication process for OPD 

Spray coating 

Excellent statistics of IV-characteristics 

NIR sensors applying the dominant design of bulk heterojunctions 

Tunable absorber (polymer-free system) 

Industrial sensor prototypes (multifunctional light-barrier up to 900 nm) 

 

Low-cost imager for SWIR 

Quantum dots as absorber 

Imaging and videos >1100 nm with hybrid organic photodiode matrix 




Acknowledgements 

Dr. Oliver Hayden 

Sandro Tedde 

Tobias Rauch 

Regina Pflaum 

Dr. Joachim Wecker 

Prof. C. Brabec 

(ex-Konarka) 

Prof. W. Heiss 

(Uni Linz) 

Prof. Moungi 

Bawendi 

(MIT) 

Thank you for your attention! 




Wishes and Hopes of Organic Electronics … 

Organic Electronics 

CMOS

Dr. Maria Sramek, Siemens AG, Erlangen - Funktionelle Farbstoffe

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