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Soft x-ray nanoanalytical tools for thin film organic electronics

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Trinity College Dublin
Trinity College Dublin

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.

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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
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 Allotropes Organic 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 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
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 Si3N4 On Al/Al2O3 resonant310eV
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 / UD : 0V intensity[a.u.] UG : -10V / UD : -10Vabsorption 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: 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)
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 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
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 LinnerAbsorption(nm-1 ) Photon Energy (eV) P3HT STXM 284.5 eV STXM cannot resolve the nanostructure !
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
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 z Cantilever

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Soft x-ray nanoanalytical tools for thin film organic electronics

  • 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

Editor's Notes

  1. Electronically bistable (organic switch) Electrocatalytically active Photoactivity