Photoemission Spectroscopy Study Of Alq₃-based Organic Light-emitting Devices

Photoelectron spectroscopy (PES) usually consists of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), synchrocyclotron photoelectron spectroscopy (SRPES) and et al. It is a nondestructive surface analysis tool, and it at best can reach 10nm below the suface of a sample. Using PES, we can obtain qualitative information about the chemical state of the element and surface band distribution. We can also gain the quantitative information via PES. Combined with bombardment of Ar+, deep profile of a sample can be obtained. So PES is perfect for surface analysis and it is widely used in many domains.In this thesis, three aspects are studied based on the research project of our team using PES.1. Study of ErF3 doped near infrared (NIR) luminescent material via PES.We demonstrated near-infrared (NIR) organic light-emitting devices (OLEDs) employing erbium fluoride (ErF3) doped into tris-(8-hydroxyquinoline) aluminum (Alq3). The device structure was ITO/N. N'-di-1-naphthyl-N, N'-diphenylbenzidine (NPB)/Alq3:ErF3/2,2',2 "-(1,3,5-phenylene) tris (1-phenyl-1H-benzimidazole) (TPBI)/Alq3/Al. ErF3 was synthesized by mixing hydrofluoric (HF) acids and erbium oxide (Er2O3) in a Teflon-lined autoclave. Room-temperature electroluminescence was observed around 1530 nm due to 4I13/2-4I15/2 transition of the Er3+. The full width at half maximum (FWHM) of the electroluminescent (EL) spectra was～50 nm.The doping mechanism of ErF3 in Alq3 is investigated by PES, LiF doped Alq3 is also studied for comparison. It is found that there is a charge transfer between host and dopant in the Alq3-LiF systems, and F- anion acts as an n-type donor. For XPS results show that Er atoms will partly replace Al atoms in ErF3 doped Alq3, and Er atoms obtain electron charge from Alq3. UPS results show that the influence of ErF3 doping to work function of Alq3 is opposite to that of LiF.The mechanism of electroluminescent is attributed to Forster energy transfer mechanism to NIR-OLED.2. We focused to analyze the O 1s spectrum in Alq3 and draw a conclusion that there is only one peak (Al-O-C) in the O 1s spectrum of the pristine Alq3, in this paper. Then we showed the chemical failure process of the Alq3 using the C 1s and O 1s core level spectra. In the beginning, the O 1s spectrum of pristine Alq3 was symmetric and had only one component. But when the pristine Alq3 was exposed to air the OH group and the water would play an important role in the O 1s spectrum due to the chemical reaction between the Alq3 and absorbed water. The component of O-C=O appears in both the C 1s and O 1s spectra after a half hour, which is caused by organic carbon contamination. The chemical failure process reminded us the damage of the surrounding contamination especially water vapor to Alq3-based OLEDs is significant. So the anti-moisture solution for Alq3-based OLEDs will be very crucial.