The Electronic Structure of Lithium-doped ZnO Thin Films Studied by X-Ray Absorption and X-Ray Photoelectron Spectroscopy
Jau-Wern Chiou1*, Cheng-Yuan Lu1, Ssu-Chi Huang2, Jen-Sue Chen2
1Department of Applied Physics, National University of Kaohsiung, Kaohsiung, Taiwan
2Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan
* Presenter:Jau-Wern Chiou,
In this work, the Li-doped ZnO (LZO) thin films were prepared by spin coating method and the percentage of Li-doping is of 0%, 3%, 5%, 10%, 20%, and 30%, respectively. We investigate how Li-doping percentage affects the electronic structure of ZnO thin films by x-ray absorption near-edge structure (XANES) and x-ray photoelectron spectroscopy (XPS). In addition to the 5%-LZO thin film, the O K- and Zn L3-edges XANES spectra of other LZO thin films reveal a decrease in the number of both O 2p and Zn 3d unoccupied states with an increase of Li-doping percentage. In other words, the Li dopant enhances the effect of O 2p-Zn 3d hybridization. However, in 5%-LZO thin film, the electron transfers from Zn to O atoms and suggesting that Li-doping increase the negative effective charge of O ions accompanying the increase of the number of O 2p-dangling bond. It is consistence with the analysis of XPS measuring results and implies that the number of O 2p-dangling bond is the main factor affecting the power conversion efficiency of the inverted solar cell structure of ITO/LZO-NPs/P3HT:ICBA/PEDOT:PSS/Au/Ag.

Keywords: x-ray absorption spectroscopy, x-ray photoelectron spectroscopy