All-Inorganic Quantum-Dot Light-Emitting Devices Prepared by Solution-Process Route Zhi Li, Khan Qasim, Jing Chen*, Wei Lei, Jiangyong Pan, Qing Li, Jun Xia, Yan Tu Display Research Center, School of Electronic Science and Engineering Southeast University Nanjing, P.R. China Abstract: We have fabricated all-inorganic quantum-dot light- emitting devices(QDLED) with NiO as a hole transporting layer and TiO 2 as a inorganic electron transporting layer. P-type NiO and n-type TiO 2 charge- transport layers were synthesized by sol-gel method using spin-coating technique. The thickness of TiO2 layer was optimized with different spin-coating speed, and studied the luminescence characteristics of devices. Results indicated devices with 4000 rpm TiO 2 layer has lower turn voltage 4.2V and higher EL intensity. Keywords: all-inorganic quantum-dot light-emitting devices (QDLED); thickness of TiO2 layer; luminescence characteristics 1. Introduction In recent years，quantum dots have been studied in many fields, as quantum dots have many special luminescence properties, which mainly includes narrow spectral emission bandwidths, broad absorption, high photoluminescence quantum efficiency, good photostability, controllable bandgap (through size tuning) and compatibility with solution processing[1]. Light emitting devices based on quantum dots saturated pure color, color can be varied directly by changing the size and composition of the quantum dots without change the preparation process, so light emitting devices based on quantum dots have attracted more and more people’s attention[2-5] .One of the primary advantages QDLED lies in the fact that they can be deposited on virtually any substrate, including glass and plastic. They are suitable for use in lightweight, robust and even rollable displays[1]. In typical structures the colloidal QDs emissive layer (EML) is sandwiched between the electron transport layer (ETL) and the hole transport layer (HTL) connected with cathode and anode, respectively [6]. Hole transport layers must have high optical transparency, good chemical stability, large ionization potential, and good electron blocking capability. Except for the excellent chemical stability, good optical, electrical，and magnetic properties, nickel oxide (NiO) nanoparticles with uniform size dispersed in solution and wet processible, which is emerging as an alternative HTL for newly quantum-dot based light emitting diode (QDLED) [7] and solar cell [8]. Nickel oxide crystallizes in cubic structure, and pure, stoichiometric NiO is an excellent insulator, at room temperature conductivity on the order of 10 - 13 S cm -1 ,while non-stoichiometric NiO is a wide bandgap p-type semiconductor [9]. TiO 2 has a wide band gap (3.9 eV) semiconductor, has been considered as the electron transport material which is thermally more stable and less sensitive to oxygen and moisture [10, 11]. Likewise, TiO 2 has higher electron mobility (µe of ~1 cm2 V-1 s-1) than that of the organic molecules (such as Alq3: µe of ~1.0×10-5 cm 2 V - 1 s -1 ), which facilitates the efficient electron transport and increases the opportunity of charge recombination [12, 13]. Moreover, TiO 2 has good optical characteristics due to its high index ratio and better wave guiding properties, which enhances the external quantum efficiency (EQE) of the QDLEDs [14]. Due to these characteristics, TiO 2 is considered a suitable candidate for ETL to be employed in the QLEDs [15]. In this paper, QDLED devices have been fabricated all-inorganic quantum-dot light-emitting with NiO/(CdSe)ZnS/TiO 2 /Al structure. The effect TiO2 spin- coating speed in the QDLEDs and its optical properties has been studied. P-88 / Z. Li SID 2014 DIGEST • 1315 ISSN 0097-966X/14/4503-1315-$1.00 © 2014 SID