2021 Fiscal Year Annual Research Report
Low Temperature Photochemical Sol-Gel Processing of Functional Thin Films and their Applications
| Project/Area Number |
20J40137
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| Research Institution | Yamagata University |
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Principal Investigator |
孫 麗娜 山形大学, 有機エレクトロニクスイノベーションセンター, 特別研究員(RPD)
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| Project Period (FY) |
2020-04-24 – 2023-03-31
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| Keywords | electron injection layer / inverted IOLEDs / Znic-alkoxides |
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| Outline of Annual Research Achievements |
The project aims to develop low-temperature solution processing of functional metal oxide thin films and their applications to organic electronics. In 2021, the work focused on application of thus obtained ZnO thin films as electron injection layer (EIL) for inverted Organic Light-Emitting Diodes (iOLEDs).Here, Znic-alkoxides precursor was used. It is spin coated and simply treated under various processing. In fact, both VUV irradiation and exposure to water vapor promote conversion of ZnO crystallization effectively. However, the resulting ZnO thin films did not work well as an EIL for iOLED at all, While ZnO thin films with mild annealing can work very well.
XPS measurements showed annealing increases the number of Zn-O bonds by decreasing the organic ligands in the ZnO films. it is found that the organic ligands bonded to the ZnO surface can effectively passivate the surface traps, blocking the carrier flow towards the unfavorable side, thus suppress the non-radiative recombination loss of carriers. further analysis showed the dielectric polarization of Zinc-organic layer at the interface between ITO and organic, can effectively stabilize the potential drop by charge trapping to facilitate electron injection to the LUMO of organic, and significantly improve the radiative recombination efficiency in devices. Consequently, the resulting current efficiency of iOLED with Znic-alkoxides thin film as EIL layer is enhanced to 25.5 cd/A, as compared to 0.000042 cd/A of the reference device.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Basically, the work has been carried on according to the original plan. In 2021, we have applied low-temperature solution processed ZnO thin films as electron injection layer (EIL) for inverted Organic Light-Emitting Diodes (iOLEDs), and investigated the effects of VUV irradiation time, exposure to water vapor, and annealing temperature on the properties of ZnO thin films and their influences on the performance of iOLED devices.
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| Strategy for Future Research Activity |
Based on the knowledge from currently discovered zinc-alkoxides precursor as an efficient electron injection layer for improved performance of iOLEDs. Effect of metal-organic precursors with various metal cations, especially interesting are those group (II) elements of Mg, Ca (II), Ba (II) and Sr (II) to envision lowering the energy barrier of electron injection, as EIL layer on the performance of iOLED devices are to be investigated. In addition, Crystallization of ZnO often result in surface roughness, which is bad for its application as an EIL for thin film devices. Ternary Zn-Sn oxides, to control the degree of crystallization by addition of Sn precursor, are to be investigated and tested.
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Research Products
(5 results)
