Dual emitters for displays based on oled compounds.

Project Director: Dr. Silviu Polosan

Project ID: 78/2011
Project Director: Dr. Silviu Polosan
Project Type: National
Project Program: IDEAS
Funded by: Romanian National Authority for Scientific Research, UEFISCDI, PN-II-ID-PCE-2011-3-0620
Contractor: National Institute of Materials Physics
Project Status: Finalized
Start Date: Saturday, 1 October, 2011
End Date: Thursday, 1 October, 2016

Project Abstract:
The electroluminescent devices (OLED) are largely built up from thin organic layers stacked between a transparent anode and a metallic cathode. The charge carriers move from different sides into the recombination/emitter layer stacked in the middle, where electrons and holes recombine and excite the dopant molecules. The structure of these organic layers and the choice of electrodes are designed to maximize the recombination process in the emissive layer, thus maximizing the light output from the OLED device.
The active layer consists of an organometallic compound dispersed in a conductive polymer. This organometallic compound (dopant) is formed from a heavy metal ion bounded by three or more ligands. The aim of this project is the obtaining of electroluminescent devices which provide at least two colors, by changing the ligands in the same organometallic compound. It is also important the determining the stability during the time of these devices to avoid the breaking of their molecular structure.

Identification of open issues or new aspects proposed for study:
a) Improving anode by using an ITO substrate followed by a thin layer of ZnO nanowires ensuring a good hole injection in the OLED device.
b) Synthesis and characterization of organometallic stable dual- emitter by using different ligands who will give different phosphorescence (red-green).
c) Selection and synthesis of transparent conducting polymers for optimization of injection-type carriers by hole-blocking layer and electron-blocking.
d) Injection control of carriers by embedding magnetic nanoparticles in a sandwich structure and the role of metallic nanoparticles which acts like electron traps and holes.

Project Objectives:
1. Theoretical modeling of processes in phosphorescent organometallic materials with two types of ligands.
2. Obtaining an organometallic compound, dual-emitter (with two types of ligands) based on Ir.
3. Dispersion of obtained organometallic compound in a transparent insulating polymer matrix for the study of physical and chemical stability by spectroscopic measurements.
4. Making an emissive layer thin film by dispersing the organometallic in a conductive polymer matrix and characterization of these films by different physicochemical methods.
5. Obtaining sandwich structures using the above emissive layer together with two different conductive polymers (hole and electron blocking) and two electrodes. Measurements of the
characteristic parameters of these sandwich structures.

6. A control injection of charge carriers in the OLED structure by embedding metal or magnetic nanoparticles for the creation of the capture centers for carriers.

1. Polosan Silviu- Dr., Senior Researcher II
2. Ciobotaru Iulia Corina - PhD., Master Chemistry Engineer
3. Iovu Horia- Prof. Dr., Experienced Researcher
4. Enculescu Ionut - Dr., Senior Researcher I
5. Tudor Elena - technician

Activity report 2011-2014 - download
Activity report 2015-download
Activity report 2016-download
Activity report 2011-2016-download

1. Optimization of IrQ(ppy)2 molecule was realized by using the spacial geometry of Ir(ppy)3 in which a phenylpiridine ligand was changed with quinoline one. The optimization was fulfilled by achieving a convergence for the energy after a few steps.

2. Obtaining of the ground state and excited states of IrQ(ppy)2 molecule - theoretical modeling by using Time-Dependent Density Functional Theory (TD-DFT). The absorption spectrum was modeled by using the ground state and excited states energies and the oscillator strengths.

3. The hybridization between Ir 5d orbitals and π ligand orbitals shows strong metallic character with phenylpyridine orbitals (66% and 43 %) and weak metallic character with quinoline ligand (16.8%). Population analysis of each metallic orbital shows a small charge delocalization on the quinoline ligand for the first molecular orbital and a strong delocalization on the phenylpyridine ligands. Solvation effects induce a tuning process for the phosphorescence by changing the matrix of the organometallic compounds which can be adjusted by the strength of intermolecular dipole-dipole interactions, using a doped guest–host molecular organic thin film system.

4. Obtaining of [(C^N)2Ir-μ-Cl]2 intermediate compound followed by the mixing with 8-quinolinol, when results IrQ(ppy)2 powder. The mixture was refluxed and passed through silicagel column.
5. Spectroscopic analisys of IrQ(ppy)2 in several solvents (CH2Cl2, ethanol). Recrystallization of IrQ(ppy)2 from CH2Cl2. Structural characterization of IrQ(ppy)2 (XRD, DSC, TGA, XPS, SEM, CL, FTIR and Raman).

6. Dispersion of IrQ(ppy)2 powder in PMMA and polystyrene matrix. Spectroscopic and structural analysis (FT-IR, Raman, DSC, TGA, SEM, CL, XPS).

7. Templateless electrochemical deposition of ZnO nanowires on ITO substrates. Uniform ZnO nanowires were successfully deposited at -900mV and 4 minutes deposition time.

8. Deposition of conductive polymers for hole transport (HTL) layer substrates. Spin-coating deposition of PEDOT and PEDOT:PSS at 6000 rpm and 30 seconds on ZnO nanowires substrates.

9. Deposition of an emissive layer containing IrQ(ppy)2 organometallic compound. Dispersion of the organometallic compound in TPD conducting polymer and spin coating on top of HTL layer at 2000 rpm and 30 seconds.

10. Deposition of ETL and metallic cathodes on top of the emissive layer. Spin-coating of BCP and Alq3 at 1000 rpm and 30 seconds for charge density increasing in the OLED’s structures. Thermal evaporation of gold on top of these structures.

11. Current-voltage characterization of obtained multilayer structures. Schottky characteristics of p-n junctions between ZnO nanowires and PEDOT conducting polymers and created OLED structures.

12. IrQ(ppy)2 has been embedded in CPB and TPD conducting polymers, between 2 to 6% wt. and deposited on the glass/ITO/PEDOT:PSS substrates.

13. In both cases, the electroluminescence shows an all over orange color as a mixture between yellow-green and red emissions coming from the two type of ligands.

14. Current-voltage measurements on CBP:IrQ(ppy)2 shows three conduction domains: a) an ohmic one; b) a space-charge-limited one and c) a free traps current.

15. Current-voltage measurement on TPD:IrQ(ppy)2 has different behaviors because the TPD polymer is an optically active one, forming intrinsic excitons which interact with the similar excitons of IrQ(ppy)2, leading to a more complicated third domain.

16. As an electron transport layer, Alq3 thin films (15 nm) were used and the aluminum cathodes (100 nm) were thermally evaporated on the top of the sandwich structures.

Didactic Activities:
1. Iulia Corina Ciobotaru - Ph.D. student of the Univ Politehnica of Bucharest, with thesis entitled
“Organic semiconducting materials for photonic applications”. The results of the project are fully
integrated into her PhD thesis - two general seminars and two in the department.

1. “Mechanisms of the charge transfer in IrQ(ppy)2-5Cl dual-emitter compounds”
S. Polosan, I.C. Radu

J. Nanosci. Nanotechnol. 13(7), 5203-5208 (2013).

2. “Dual emitter IrQ(ppy)2 for OLED applications: Synthesis and spectroscopic analysis”
I.C.Ciobotaru, S.Polosan, C.C.Ciobotaru
J. Luminescence, 145, 259-262 (2014).

3. "Structural characteristics of Iridium dual emitter organometallic compound"
S. Polosan, I.C. Ciobotaru, I. Enculescu, C.C. Ciobotaru
Journal of Materials Research, 29(23), 2898-2904 (2014).

4. "Electroluminescence of OLED based IrQ(ppy)2-5Cl organometallic compound: Theoretical considerations"
S. Polosan, I.C. Ciobotaru
J. Optoelectronics and Advanced Materials, 16(1-2), 87-92 (2014).

5. "Embedding of IrQ(ppy)2 organometallic compounds in polypyrrole conducting polymer for OLED`s applications"
I.C. Ciobotaru, E. Matei, C.C. Ciobotaru, S. Polosan
Synthetic Metals, 198,  323–328, (2014).

6. "Absorption, phosphorescence and Raman spectra of IrQ(ppy)2 organometallic compound"
S. Polosan, I.C. Ciobotaru, T. Tsuboi
Materials Chemistry and Physics, 162(15),  822-830 (2015).

7. “Templateless electrodeposition ZnO nanowires for charge transport optimization in OLED structures”
S. Polosan, E. Matei, I.C. Ciobotaru, C.C. Ciobotaru
Materials Research Express, 3,  105018 (2016).

8. “Charge Transport in CBP and TPD Thin Film Polymers Doped with IrQ(ppy)2 Phosphorescent
C.C. Ciobotaru, I.C. Ciobotaru, S. Polosan
Journal of Electronic Materials, 47(2), 1490-1496 (2018).

9. "Crystallization properties of IrQ(ppy)2 organic complex films"
S. Polosan, C.C. Ciobotaru, I.c. Ciobotaru,T. Tsuboi
Journal of Materials Research, 32(9),  1735 (2017).

10. „Enhancement of the electroluminescence of organic light emitting devices based on IrQ(ppy)2 by doping with metallic and magnetic nanoparticles”
C.C. Cioboratu, I.C. Ciobotaru, G. Schinteie, R. Negrea, S. Polosan
Materials Science in Semiconductor Processing, 72, 78 (2017).

11. "Charge carrier traps in tris-(8-hydroxyquinoline) aluminum"
M. Secu, S. Polosan
J. Luminescence, 194,  91 (2018).

A number of 11 ISI publications, with a total 19.852 impact factor and 1 topic for PhD thesis resulted during the project.

1. I.C.Radu, S. Polosan, T. Tsuboi, "Dual Emitters for displays based on OLED compounds",12th International Balkan Workshop on Applied Physics, Constanţa, July 6-8, 2011.
2. S. Polosan, I.C.Radu, "Mechanisms of the charge transfer in IrQ(ppy)2-5Cl dual-emitter compounds", EMRS Spring Meeting, 14-18 Mai, 2012, Strasbourg, France.
3. I.C.Radu, S. Polosan, "Photophysical and magnetic properties of IrQ(ppy)2–5Cl for Organic Light Emitting Device applications", E-MRS Spring Meeting, 14-18 Mai, 2012, Strasbourg, France
4. I.C.Radu, C.C.Ciobotaru, S. Polosan, "Spectroscopy and structural analysis of Iridium intermediate compound", The 8th General Conference of Balkan Physical Union, 5-7 July 2012, Constanta, Romania.
5. S. Polosan, I.C.Radu, "Organometallic materials for low energy consumption OLED devices", The 8th General Conference of Balkan Physical Union, 5-7 July 2012, Constanta, Romania.
6. S. Polosan, I.C.Radu, "Organometallic Compounds and Their Applications", The 7th InternationalConference on Advanced Materials, ROCAM 2012, 28-31 August 2012, Brasov, Romania.
7. S. Polosan, I.C.Radu, "Phosphorescence of Iridium based organometallic compounds in Magnetic Field", 8th International Conference on Luminescent Detectors and Transformers of Ionizing Radiation -LUMDETR 2012, 9-14 Septembrie 2012, Halle, Germany.
8. I.C.Ciobotaru, S.Polosan, C.C.Ciobotaru, "Dual emitter IrQ(ppy)2 for OLED applications- synthesis and spectroscopic analysis", Sixth International Meeting on Molecular Electronics, December 3-7 2012,Grenoble, France.

9. S.Polosan, I.C.Ciobotaru, L.Stoflea, "Structural characteristics of IrQ(ppy)2 organometallic compound", Sixth International Meeting on Molecular Electronics, December 3-7 2012, Grenoble, France.
10. I.C. Ciobotaru ,S. Polosan, "Energy transfer in composite IrQ(ppy)2–5Cl: polystyrene layers", Third International Conference on Multifunctional, Hybrid and Nanomaterials, 21-23 May 2013, Sorrento, Italy.
11. S. Polosan, I.C. Ciobotaru, C.C. Ciobotaru, "Dual emitter organometallic compounds: thermal and structural characteristics", 13th International Balkan Workshop on Applied Physics, Constanta, Romania, 4-6 July, 2013
12. I.C. Ciobotaru, S. Polosan, C.C. Ciobotaru, H. Iovu, "New Ir(ppy)2 organometallic compound for OLED applications: synthesis and optical characterization", 13th International Balkan Workshop on Applied Physics, Constanta, Romania, 4-6 July, 2013
13. S. Polosan, I.C. Ciobotaru, C.C. Ciobotaru, "Iridium dual emitter organometallic compound: Thermal and structural analysis", 6th International Symposium on Flexible Organic Electronics (ISFOE13), 8‐11, July 2013, Thessaloniki, Greece.
14. I.C. Ciobotaru, S. Polosan, I. Enculescu, C.C.Ciobotaru, H. Iovu, "IrQ(ppy)2 in Poly(methyl-methacrylate) matrix for OLED applications", 6th International Symposium on Flexible Organic Electronics (ISFOE13), 8‐11 July 2013, Thessaloniki, Greece.
15. S. Polosan, "Electrochemical deposition of organometallic compounds", 10th International Conference on Electroluminescence and Optoelectronic Devices (ICEL 10), 31.08-3.09 2014, Cologne, Germany.

16. I.C. Ciobotaru, E. Matei, "Polypyrrole/ IrQ(ppy)2 composite films prepared by electrochemical deposition for OLED’s applications", 10th International Conference on Electroluminescence and Optoelectronic Devices (ICEL 10), 31.08-3.09 2014, Cologne, Germany.
17. I.C. Ciobotaru, S. Polosan, H. Iovu, "Influence of crystallization on the phosphorescence of IrQ(ppy)2 organometallic compound in OLED’s applications", E-MRS 2014 Spring Meeting, 25-31 May, 2014, Lille, France.
18. C.C. Ciobotaru, S. Polosan, "Embedding of IrQ(ppy)2 organometallic compounds in polypyrrole conducting polymer", E-MRS 2014 Spring Meeting, 25-31 May, 2014, Lille, France.
19. S. Polosan, "Electrochemical deposition of organometallic/polypyrrole composites for OLED applications", 14th International Balkan Workshop on Applied Physics, 2-4 July 2014, Constanta, Romania.
20. S. Polosan, "Charge transport optimization in OLED structures by using ZnO nanowires", ISFOE 15, 6-9 July, 2015, Thesalonic, Greece.
21. S. Polosan, E. Matei, I.C. Ciobotaru, C.C. Ciobotaru, "ZnO nanowires in organic light emitting diodes", The 15th International Balkan Workshop on Applied Physics, Constanta, 2-4 July, 2015.

Project Contact Person:
1. Polosan Silviu - Dr. Senior Researcher I
Materials and Multifunctional Nanostructures
National Institute of Materials Physiscs
email: silv@infim.ro
tel: +40213690185

2. Ciobotaru Iulia Corina - Dr. Senior Researcher
Materials and Multifunctional Nanostructures
National Institute of Materials Physiscs
email: corina.ciobotaru@infim.ro
tel: +40213690185


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