| Abstract [eng] |
In 1987 new organic electroluminescent compounds appeared. The layers of these compounds exhibited luminescence properties under current excitation [1] and they were named Organic Light Emitting Diodes (OLEDs). These comparatively cheap and quickly produced in terms of fabrication organic light emitting devices have opened new research area for scientists. Nowadays OLEDs are used in the flexible screen market and are rapidly engaging towards general illumination market. In 2014, “Konica Minolta” began mass production of flexible broad spectra OLED based sheets with the luminous efficiency of 131 lm/W for general lighting [2, 3]. But OLEDs are suffering from spectral stability problems thus far. The efficiency of blue emitters was highly improved using TADF (Thermally Activated Delayed Fluorescence) emitters [4]. Also optimal and requiring less technological steps in terms of price OLED structure is in search for broad spectra illumination. In this dissertation we are going to present benzo- and naphthoquinoline derivatives (based on already known synthons) with different substituents: chlorine, tetrazole, iminophosphorane, amine; and 1,8-naphthyridine based compounds having a non-planar bicyclic moiety: bicyclo[3.3.1]nonane, bicyclo[3.3.0]octane and camphor which were synthetized at the Faculty of Chemistry, Vilnius university. Also we are going to present these materials as potential emitters in multi-layered OLED systems. All results are published in corresponding research papers: [5] and [6]. In addition, to improve broad spectra stability the hybrid OLEDs (QD OLEDs) with Ir(Fppy)3 and CdSxSe1-x/ZnS quantum dots (QDs) as emissive layers (EmL) were shown. The results are published in research paper [7]. Work goals and objectives of the dissertation covers research, characterization of quinolone and 1,8-naphthyridine derivatives. Also fabrication, characterization of OLEDs and hybrid QD OLEDs (whose emissive layers are based on quinoline, 1,8-naphtyridine compounds and Ir(Fppy)3/CdSxSe1-x/ZnS QDs respectively) are shown. Small molecular weight quinoline derivatives are used as fluorescent dyes or as emissive, charge transport layers in OLED devices. Some of synthesized quinoline derivatives are published earlier [ , , , , ]. The first aim of this work was to investigate luminescence properties of the newly synthesized quinoline derivatives with chlorine, tetrazole, iminophosphorane, amine substituents for broad spectra OLEDs applications. Also 1,8-naphtyridine derivatives were synthetized. As mentioned previously in the literature [ , , ] 1,8-naphtyridine compounds are used as hole, electron transport and emissive layers in OLEDs. Still, emissive layers with 1,8-naphtyridine derivatives showed concentration dependent photoluminescence (PL) quenching and unstable thin –film formation. To overcome these issues nonplanar bicyclic moieties (bicyclo[3.3.1]nonane, bicyclo[3.3.0]octane and camphor) were attached. And the second aim of this work was to investigate luminescence properties of these newly synthetized 1,8-naphtyridine compounds for broad spectra OLEDs applications. The third aim of this work was to extend OLED spectra utilizing CdSxSe1-x/ZnS quantum dots. It is worth to notice that few organic emissive layers giving broad emission spectra in OLEDs degrade differently in the time scale and their emission spectrum depends on applied external voltage. Since quantum dots (QDs) are stable, they may partially solve the colour shift problem and prolong device lifetime. QDs have narrow emission spectra [ ] which do not depend on applied voltage. Herein, we report broad spectrum hybrid quantum dot organic light emitting diodes (QD OLEDs) based on two emission layers (EmL): blue-green small organic molecule emitter Ir(Fppy)3 which does not show any colour shift and red emitter made from core-shell type CdSxSe1-x/ZnS QDs when concentration of these QDs solution is changed. Main objectives 1. To investigate how different substituents: chlorine, tetrazole, iminophosphorane, amine in quinoline derivatives and different substituents: bicyclo[3.3.1]nonane, bicyclo[3.3.0]octane and camphor in 1,8-naphtyridine derivatives change their PL and absorbance spectra, the values of quantum yields (QY) and ionization potential values. 2. To demonstrate experimentally how different substituents used as emissive layer of chinoline and 1,8-naphtyridine derivatives change electroluminescence (EL) spectra of OLEDs. 3. To determine a chemical compatibility between chinoline, 1,8-naphtyridine derivatives and CdSxSe1-x/ZnS QDs. 4. To show and to optimize in terms of concentration of QDs broad spectra hybrid OLEDs utilizing emissive layers made from organic material Ir(Fppy)3 and from CdSxSe1-x/ZnS QDs. Novelty All chinoline and 1,8-naphtyridine derivatives with different substituents as well as OLEDs based on emissive layers made from these compounds and hybrid OLEDs based on material Ir(Fppy)3 and on CdSxSe1-x/ZnS QDs, described in these thesis, are new and have not been reported before. Main new results. 1. Measured values of chinoline derivatives of the HOMO, the LUMOopt energy levels and optical band gap Eg_opt were in range EHOMO=[-5,9; -5,5] eV, ELUMO=[-3,6; -3] eV, Eg_opt=[2; 2,8] eV. The difference between PL spectra peaks in the solutions and in the layers of the same materials ΔλPL=[-42, 84] nm. The PL solvatochromaticity of quinoline derivatives in toluene, chloroform and 2-methoxyethanol is Δλ=[12,77] nm. The value of Eg_opt energy increases in all quinoline groups while substituents are changed as follows: amine, tetrazole, imunophosphorane and chlorine. Additional benzene rings in the molecules lowered Eg_opt energy value and shifted PL and absorbance spectra peaks towards shorter wavelengths. The QY value in chloroform solution reached 49% while (3c) material was used. The QY values of the other quinoline derivatives in chloroform solution were between 0,5% and 17%. The QY values of the organic layers did not exceed 10% respectively. 2. OLEDs with structure ITO/TPD/EmL/TmPyPB/Alq3/LiF/Al showed EL spectra in blue and green region when (2c), (2d), (2e), (2f) and (3c), (5b), (5f) chinoline derivatives were used in the emissive layer. When (3d), (4b), (4c), (4f) and (5g) derivatives were used as EmL in ITO/TPD/EmL/TmPyPB/Alq3/LiF/Al OLEDs the broad visible spectra light were obtained due to EL component originated from TPD material. 3. Measured values of 1.8-naphtyridine derivatives of the HOMO, the LUMOopt energy levels and optical band gap Eg_opt were in range EHOMO=[-5,9; -5,4] eV, ELUMO=[-3,4; -2,4] eV, Eg_opt=[2,3; 3] eV. The bathochromic shift between PL spectra peaks in the solutions and in the layers of the same materials was observed. (18), (36) and (37) 1,8-naphtyridine derivatives had the longest π conjugation in the group and PL QY in the layer of these materials reached 16%, 4% and 11% respectively. 4. OLEDs with structure ITO/TPD/EmL/TmPyPB/Alq3/LiF/Al showed EL spectra from red-orange to blue region when 1,8-naphtyridine derivatives: (15), (32), (35), (30), (28), (34), (31), (36), (17), (18), (26), (27), (33) and (29) were used in the EmL. When duplex non-planar “V” conformation molecules ((16), (19) and (21)) were used as EmL in ITO/TPD/EmL/TmPyPB/Alq3/LiF/Al OLEDs the broad visible spectra light were measured. The white light of these OLEDs could be originated from emission of emissive layer as well as emission of TPD and TPD/EmL interlayer. 5. Chinoline, 1,8-naphtyridine derivatives and CdSxSe1-x/ZnS QDs in toluene are not chemically compatible because toluene dissolves chinoline and 1,8-naphtyridine derivatives. For that reason hybrid OLEDs were made using Ir(Fppy)3 material which is chemically compatible with the CdSxSe1-x/ZnS QDs dissolved in toluene. 6. We have fabricated broad spectra light-emitting diodes based on organic material Ir(Fppy)3 emissive layer and CdSxSe1-x /ZnS QDs emissive layer with different concentrations of QDs. The optimal concentration of QDs in toluene is 5mg/ml. The wide EL emission properties of Ir(Fppy)3 and the simultaneous existence of incomplete energy transfer from Ir(Fppy)3 to CdSxSe1-x /ZnS QDs and carrier trapping directly on CdSxSe1-x /ZnS QDs lead to broad light emission in visible spectrum. This is the simplest component and structure in the realization of broad spectrum QD OLEDs. Our results show that an organic and inorganic hybrid with proper concentration as the active medium could be a promising route to broad spectra QD OLEDs. Statements to defend 1. The origin of broad visual spectra in OLEDs based on EmL of quinoline derivatives: (3d), (4b), (4c), (4f) and (5g); is the emission from these chinoline derivatives and TPD. 2. The origin of broad visual spectra in OLEDs based on EmL of duplex non-planar “V” conformation 1,8-naphtyridine derivatives is the emission from emitters, from TPD and from TPD/EmL interlayers. 3. The wide EL emission properties of Ir(Fppy)3 and the simultaneous existence of incomplete energy transfer from Ir(Fppy)3 to CdSxSe1-x /ZnS QDs and carrier trapping directly on CdSxSe1-x /ZnS QDs lead to broad light emission in visible spectrum in ITO/TPD/Ir(Fppy)3/QD/Alq3/LiF/Al structure. Layout of the thesis The dissertation consists of 7 Chapters. The first chapter is Preface. In the second chapter we will find the history of light sources, the goals and objectives of this work, novelty, new results, and statements to defend. In addition, the articles and conference presentations concluding the presented data are listed at the second chapter. In this chapter the theory of small organic molecules and quantum dots as well as the basic structures of OLED and of hybrid QD OLED are presented. In the third chapter we will find information about fabrication technology of the OLEDs and QD OLEDs described in these thesis. The experimental techniques and the images of microscopes, PL, QY, ionization potential results of quinoline, 1,8-naphtyridine derivatives as well as of QD OLEDs are presented in the fourth chapter. Original EL spectra results of fabricated OLEDs with chinoline, 1,8-naphtyridine compounds and of QD OLEDs are presented in the fifth chapter. The main conclusions and results of these theses are presented in the sixth chapter. The seventh chapter consists of the list of references cited in this work. |
