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Xin L.-W.,Tianjin University of Technology | Xin L.-W.,Key Laboratory of Display Materials and Photoelectric Devices of Ministry of Education | Xin L.-W.,Tianjin Key Laboratory of Photoelectric Materials and Devices | Wu X.-M.,Tianjin University of Technology | And 17 more authors.
Chinese Physics B

We investigate the electron injection effect of inserting a thin aluminum (Al) layer into cesium carbonate (Cs2CO3) injection layer. Two groups of organic light-emitting devices (OLEDs) are fabricated. For the first group of devices based on Alq3, we insert a thin Al layer of different thickness into Cs2CO3 injection layer, and the device's maximum current efficiency of 6.5 cd/A is obtained when the thickness of the thin Al layer is 0.4 nm. However, when the thickness of Al layer is 0.8 nm, the capacity of electron injection is the strongest. To validate the universality of this approach, then we fabricate another group of devices based on another blue emitting material. The maximum current efficiency of the device without and with a thin Al layer is 4.51 cd/A and 4.84 cd/A, respectively. Inserting a thin Al layer of an appropriate thickness into Cs2CO3 layer can result in the reduction of electron injection barrier, enhancement of the electron injection, and improvement of the performance of OLEDs. This can be attributed to the mechanism that thermally evaporated Cs2CO3 decomposes into cesium oxides, the thin Al layer reacts with cesium oxides to form Al-O-Cs complex, and the amount of the Al-O-Cs complex can be controlled by adjusting the thickness of the thin Al layer. © 2015 Chinese Physical Society and IOP Publishing Ltd. Source

Huang Q.-S.,Institute of Material Physics | Huang Q.-S.,Key Laboratory of Display Materials and Photoelectric Devices of Ministry of Education | Huang Q.-S.,Tianjin University of Technology | Li L.,Institute of Material Physics | And 14 more authors.
Optoelectronics Letters

Undoped ZnS nanocrystals (NCs) with different precursor molar ratios of [S2-]/[Zn2+] are prepared by the chemical precipitation method. The structural and optical properties of the samples are characterized by the X-ray diffraction (XRD) spectra, photoluminescence (PL) spectra and PL decay spectra. The XRD analysis shows that the crystal quality of ZnS NCs becomes better and the grain size is larger at higher [S2-]/[Zn2+] ratios. The PL peaked at 430 nm decreases with the [S2-]/[Zn2+] ratio increasing, which is ascribed to the structure defects of NCs. A multi-exponential decay time curve with hundreds of picoseconds, several nanoseconds and tens of nanoseconds is obtained, which also shows a distinct and regular change with [S2-]/[Zn2+] ratio. It is indicated that the PL and emission decay properties of ZnS NCs mainly depend on the change of the defects number from different particle sizes. © 2010 Tianjin University of Technology and Springer-Verlag Berlin Heidelberg. Source

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