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Solution-Processed Hybrid Light-Emitting Devices Comprising TiO 2 Nanorods and WO 3 Layers as Carrier-Transporting Layers

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ABSTRACT

The goal of this research is to prepare inverted light-emitting devices with improved performance by combining titanium dioxide (TiO2) nanorods and tungsten trioxide (WO3) layer. TiO2 nanorods with different lengths were established directly on the fluorine-doped tin oxide (FTO) substrates by the hydrothermal method. The prepared TiO2 nanorods with lengths shorter than 200 nm possess transmittance higher than 80% in the visible range. Inverted light-emitting devices with the configuration of FTO/TiO2 nanorods/ionic PF/MEH-PPV/PEDOT:PSS/WO3/Au were constructed. The best device based on 100-nm-height TiO2 nanorods achieved a max brightness of 4493 cd/m2 and current efficiency of 0.66 cd/A, revealing much higher performance compared with those using TiO2 compact layer or nanorods with longer lengths as electron-transporting layers.

No MeSH data available.


a Device architecture and b energy level diagram of the whole device
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Fig1: a Device architecture and b energy level diagram of the whole device

Mentions: In this research, we demonstrate the preparation and characterization of TiO2 nanomaterials, including nanoparticles, nanorods, and compact layer, which can be used as an ETL for the fabrication of hybrid-inverted light-emitting devices. TiO2 nanorods and nanoparticles were prepared on the FTO substrates by the hydrothermal method without using either templates or seeds. This is because the FTO substrate also has the tetragonal rutile structure, and the lattice mismatch between the tetragonal FTO (a = b = 0.4687 nm) and the rutile TiO2 (a = b = 0.4593 nm) is only 2% [21]. To further improve device performance, ultra-thin layers of tungsten trioxide (WO3) and ionic PF derivative are incorporated. WO3 has been reported to serve as the HIL for application in organic light-emitting and photovoltaic devices [22–24]. The ionic PF material carrying hexafluorophosphate (PF6−) counterions as wetting agent was synthesized and demonstrated in this study. Inverted light-emitting devices with the configuration of FTO/TiO2 nanorods/ionic PF/MEH-PPV/PEDOT:PSS/WO3/Au were fabricated and evaluated. The illustration of the device structure is shown in Fig. 1a, and the energy level diagram of the whole device is illustrated in Fig. 1b. It is seen that electron injection from FTO to TiO2 layer is undisturbed [25]. To overcome the large energy barrier between TiO2 and the active layer MEH-PPV, a thin layer of ionic PF was introduced; besides, this ionic PF also serves as the wetting layer to increase contact between inorganic TiO2 and organic MEH-PPV layers. On the other hand, the valence band of WO3 lies between the highest occupied molecular orbital of PEDOT:PSS and the work function of gold electrode that is favored for hole injection from the anode [22]. The PEDOT:PSS layer is incorporated between WO3 and the active layer to increase hole transfer. The recombination of electrons and holes in the active layer MEH-PPV results in electroluminescence (EL) under bias operation. The features of inverted architecture and solution process for deposition of organic and inorganic layers in this study provide a promising way to low-cost manufacturing in the future.Fig. 1


Solution-Processed Hybrid Light-Emitting Devices Comprising TiO 2 Nanorods and WO 3 Layers as Carrier-Transporting Layers
a Device architecture and b energy level diagram of the whole device
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121115&req=5

Fig1: a Device architecture and b energy level diagram of the whole device
Mentions: In this research, we demonstrate the preparation and characterization of TiO2 nanomaterials, including nanoparticles, nanorods, and compact layer, which can be used as an ETL for the fabrication of hybrid-inverted light-emitting devices. TiO2 nanorods and nanoparticles were prepared on the FTO substrates by the hydrothermal method without using either templates or seeds. This is because the FTO substrate also has the tetragonal rutile structure, and the lattice mismatch between the tetragonal FTO (a = b = 0.4687 nm) and the rutile TiO2 (a = b = 0.4593 nm) is only 2% [21]. To further improve device performance, ultra-thin layers of tungsten trioxide (WO3) and ionic PF derivative are incorporated. WO3 has been reported to serve as the HIL for application in organic light-emitting and photovoltaic devices [22–24]. The ionic PF material carrying hexafluorophosphate (PF6−) counterions as wetting agent was synthesized and demonstrated in this study. Inverted light-emitting devices with the configuration of FTO/TiO2 nanorods/ionic PF/MEH-PPV/PEDOT:PSS/WO3/Au were fabricated and evaluated. The illustration of the device structure is shown in Fig. 1a, and the energy level diagram of the whole device is illustrated in Fig. 1b. It is seen that electron injection from FTO to TiO2 layer is undisturbed [25]. To overcome the large energy barrier between TiO2 and the active layer MEH-PPV, a thin layer of ionic PF was introduced; besides, this ionic PF also serves as the wetting layer to increase contact between inorganic TiO2 and organic MEH-PPV layers. On the other hand, the valence band of WO3 lies between the highest occupied molecular orbital of PEDOT:PSS and the work function of gold electrode that is favored for hole injection from the anode [22]. The PEDOT:PSS layer is incorporated between WO3 and the active layer to increase hole transfer. The recombination of electrons and holes in the active layer MEH-PPV results in electroluminescence (EL) under bias operation. The features of inverted architecture and solution process for deposition of organic and inorganic layers in this study provide a promising way to low-cost manufacturing in the future.Fig. 1

View Article: PubMed Central - PubMed

ABSTRACT

The goal of this research is to prepare inverted light-emitting devices with improved performance by combining titanium dioxide (TiO2) nanorods and tungsten trioxide (WO3) layer. TiO2 nanorods with different lengths were established directly on the fluorine-doped tin oxide (FTO) substrates by the hydrothermal method. The prepared TiO2 nanorods with lengths shorter than 200 nm possess transmittance higher than 80% in the visible range. Inverted light-emitting devices with the configuration of FTO/TiO2 nanorods/ionic PF/MEH-PPV/PEDOT:PSS/WO3/Au were constructed. The best device based on 100-nm-height TiO2 nanorods achieved a max brightness of 4493 cd/m2 and current efficiency of 0.66 cd/A, revealing much higher performance compared with those using TiO2 compact layer or nanorods with longer lengths as electron-transporting layers.

No MeSH data available.