Functional Dyes for Organic Semiconductor Sensors

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1 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 Erlangen Phone: maria.sramek@siemens.com Web: Page 1 May 2012 Dr. M. Sramek

2 Motivation R&D Program System Solutions Organic semiconductor Nanorods Quantum dots nanocrystals Fullerenes Carbon nanotubes Working Nanotechnology From Materials to Business Concepts X-ray imaging Industrial sensors In-vitro diagnostics Open innovation Page 2 May 2012 Dr. M. Sramek

3 Outline 1. Introduction 2. Processing 3. Applications for Visible and Infrared Range Page 3 May 2012 Dr. M. Sramek

4 Outline 1. Introduction 1.a - Review 1.b - Organic Photodiodes 2. Processing 3. Applications for Visible and Infrared Range Page 4 May 2012 Dr. M. Sramek

Crystalline and impurityfree substrates 12

Roll-to-roll Aim: Integration to cut costs

material costs/purity - Large footprint vs.

5 Silicon is Gods Material and What About Organics? Crystalline and impurityfree substrates 12 /30 cm Workhorse - wafer Molecules/Polymers Roll-to-roll 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 Page 5 May 2012 Dr. M. Sramek

6 Nobel History of Conductive Organics Fullerenes ( Buckyballs ) Conductive Polymers Replace silicon and organics beyond silicon bandgap limit Page 6 May 2012 Dr. M. Sramek

7 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 Page 7 May 2012 Dr. M. Sramek

8 Device Fabrication Silicon Organics Page 8 May 2012 Dr. M. Sramek

9 Revolution to Evolution Example of OLED Display Developments Uni Bayreuth 1994 Sony 11-inch OLED 2008 Philips, Passiv Matrix 1999 Sanyo-Kodak 2000 Samsung 2009 Mitsubishi 155-inch OLED 2009 BenQ/Siemens Activ Matrix 2006 The Holy Grail Flexible TV Page 9 May 2012 Dr. M. Sramek

10 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 Page 10 May 2012 Dr. M. Sramek

11 Outline 1. Introduction 1.a - Review 1.b - Organic Photodiodes 2. Processing 3. Applications for Visible and Infrared Range Page 11 May 2012 Dr. M. Sramek

12 Organic Diode Solid state: PN-junction Organic: Bulk heterojunction O 4+ O OMe Fullerene p-type n-type O 4+ + O OMe C - O OMe C 2- O OMe C - C - O OMe O OMe C - C 3- O OMe Depletion region C - O OMe C 3- C 3- O OMe C 3- C - C- C 2- O OMe C 2- C - O OMe C 4- O C 2- Anode Cathode C 3- OMe Semiconducting polymer 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 ) Page 12 May 2012 Dr. M. Sramek

13 Layer Stack of Organic Photodiodes (OPDs) Encapsulation Cathode Bulk heterojunction (P3HT/PCBM/quantum dots) ITO (Anode) Interlayer Substrate ITO (Anode) Page 13 May 2012 Dr. M. Sramek

14 VIS to NIR Spectral Sensitivity 1,0 Organic absorber up to ~1 µm Inorganic absorber >1 µm 0, EQE (normalized) 0,6 0,4 EQE (%) Wavelength (nm) 0,2 0,0 Standard P3HT/PCBM (cf. plastic solar cells) Low bandgap absorber Wavelength (nm) Page 14 May 2012 Dr. M. Sramek

15 Current/Voltage Characteristics 10 1 Statistics over 100 devices Current Density (ma/cm²) AM 1.5 (solar) µw/cm 2 Dark current OPD active area 1 cm² Current density (ma/cm 2 ) Current density (ma/cm 2 ) 1x10-4 1x10-4 8x10-5 6x10-5 4x10-5 2x ,35 0,30 0,25 0,20 0,15 Dark currents 5V.dark 1V.dark Photocurrents Voltage (V) 5V.light 1V.light Reverse bias Forward bias Page 15 May 2012 Dr. M. Sramek

16 Outline 1. Introduction 2. Processing 3. Applications for Visible and Infrared Range Page 16 May 2012 Dr. M. Sramek

17 Coating Techniques Comparison: Spin coating / Doctor blading / Spray coating PEDOT:PSS Spin coating Doctor blading Spray coating Page 17 May 2012 Dr. M. Sramek

Layer roughness is not a limitation Low/high throughput technique Scalable technology Movie Spray coating of

18 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) Page 18 May 2012 Dr. M. Sramek

19 Outline 1. Introduction 2. Processing 3. Applications for Visible and Infrared Range Page 19 May 2012 Dr. M. Sramek

20 Application in the Visible Range: Organic Matrix X-Ray Detector Backplane Pixels Processed panel X-Ray image of hand phantom: Page 20 May 2012 Dr. M. Sramek

21 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 Acknowledgements: Easy and fast production processes Large area (cm² range) Thin (< 1mm) Semitransparent Page 21 May 2012 Dr. M. Sramek

22 Dynamic Response and f -3dB Signal (20*log(U/U 0 )) [db] Signal [db] -3dB f -3bB = 130 KHz k 10k 100k Frequency [Hz] Active area: 0.7 cm 2 Light source: - 1 KingBright SMD Chip LED KPL-3015SRC-PRV ( peak ~660 nm) super bright red light - Light intensity ~ 130 µw/cm² Page 22 May 2012 Dr. M. Sramek

Application in the NIR Range: Light Barrier with OPDs Motivation Specification

barrier applications Show that OPDs can substitute silicon @ NIR Optic-free

respect to active area (mm²-cm²) Quadrant functionality: - Self-alignment of

23 Application in the NIR Range: Light Barrier with OPDs Motivation Specification Demonstrate potential of organic photodiodes for new multidimensional light barrier applications Show that OPDs can substitute 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 Page 23 May 2012 Dr. M. Sramek

5 µm steps @ 15 X-axis -7,0 40 42 44 46 48 50 52 54 Time (s) X Y ( B D) ( A C) A B C D ( A B) ( C D)

24 Organic Quadrant Sensor (~4 cm² Active Area) Resolution Limit ~1 µm 1,0 0,0 Distance (µm) -1,0 Y-axis -2,0-3,0-4,0-5,0-6,0 1.5 µm 15 X-axis -7, Time (s) X Y ( B D) ( A C) A B C D ( A B) ( C D) A B C D 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 Page 24 May 2012 Dr. M. Sramek

25 Application in the NIR Range: PSD/Light 660 nm Demonstrator 4 Quadrant OPD Light Barrier Conveyor belt Implementation Page 25 May 2012 Dr. M. Sramek

NIR OPDs with a Small Molecule Absorber: Squaraine (SQ+PCBM = Polymer-Free BHJ) EQE [%] 100 80 60 40 20 External quantum efficiency EQE 0 V - 1 V - 2 V - 3 V - 4 V - 5 V - 6 V - 7 V 0 400 600 800

26 NIR OPDs with a Small Molecule Absorber: Squaraine (SQ+PCBM = Polymer-Free BHJ) EQE [%] External quantum efficiency EQE 0 V - 1 V - 2 V - 3 V - 4 V - 5 V - 6 V - 7 V Wavelength [nm] Current Density [ma cm -2 ] IV-characteristic 532 nm Solar 870 nm Dark Voltage [V] NIR peak sensitivity ~800 nm (tunable); low absorption in visible spectrum Dynamic response: -3 ~150 khz (~1 cm² active area) Synthesis yield >90% (effortless up-scaling) Key advantage: Low cost absorber; no extensive polymer purification needed Page 26 May 2012 Dr. M. Sramek

f -3dB = 100 KHz doctorbladed -6 10 100 1k 10k 100k 1M

27 Small Molecule Absorber Squaraine: Dynamic Response and f -3dB sprayed Signal (20*log(U/U 0 )) [db] OPD response f -3dB f -3dB = 100 KHz doctorbladed k 10k 100k 1M Frequency [Hz] Reverse bias: -2V applied Page 27 May 2012 Dr. M. Sramek

28 Application in the SWIR Range: Pushing The Limits of OPDs with Quantum Dots QD range Visible Application: Photography Si Bandgap NIR Imaging ( µm): - Active night vision systems (NIR source) - Security applications (machine vision) - Tomography (Tissue scanning) MIR Imaging (3-5 µm): - Thermal Imaging - Passive night vision systems Page 28 May 2012 Dr. M. Sramek

Hybrid Organic/Colloidal Photodiodes Photosensitive layer: Bulk heterojunction (P3HT:PCBM) with embedded PbS QD absorber Imager: 256x256 pixels with 154 µm pixel pitch Schematic layout of an

29 Hybrid Organic/Colloidal Photodiodes Photosensitive layer: Bulk heterojunction (P3HT:PCBM) with embedded PbS QD absorber Imager: 256x256 pixels with 154 µm pixel pitch Schematic layout of an a-si active matrix TFT panel with OPDs T. Rauch et al., Near-infrared imaging with quantum dot sensitized organic photodiodes, Nature Photonics, 3, (2009) Page 29 May 2012 Dr. M. Sramek

30 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 Page 30 May 2012 Dr. M. Sramek

31 Current/Voltage Characteristic and Lifetime I-V characteristics High photoresponse for polychromatic light >870 nm Stable diode rectification ratio up to +/-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 Page 31 May 2012 Dr. M. Sramek

Energy Band Diagram QD can act as sensitizer and as traps

ligands and the conductivity is orders of magnitudes lower

energy barrier for electron transfer between QD and PCBM;

alignment between P3HT and the PbS QD Almost flat band

PbS QD (first excitonic transition) Hole transfer might be

32 Energy Band Diagram QD can act as sensitizer and as traps PbS 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 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) Hole transfer might be possible from QDs to P3HT and/or to PEDOT Page 32 May 2012 Dr. M. Sramek

SWIR-Imaging Images @ 1310 nm Movies @ 1310 nm Si works

(154 µm pixel pitch) Video shows 2 woodlice (young

33 SWIR-Imaging 1310 nm 1310 nm Si works only up to 1100 nm! Shadow cast of a slide (flat fielding) Original slide showing a monarch butterlfly 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) Page 33 May 2012 Dr. M. Sramek

34 Conclusion Motivation: Replace 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 Page 34 May 2012 Dr. M. Sramek

35 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! Page 35 May 2012 Dr. M. Sramek

36 Wishes and Hopes of Organic Electronics CMOS Organic Electronics Page 36 May 2012 Dr. M. Sramek

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