Fig. 5: Depth profiling of chemical compositions.
a HAADF-STEM image (left, scale bar: 50 nm) of the cross-section of a QLED. The iDPC-STEM images zooming in at the Ag/Zn interfaces of the pristine (top right) and aged (bottom right) devices are shown for comparison (scale bar: 5 nm). b Schematic diagram of the depth profiling analysis of the QLED (left), and the resolved chemical compositions at the ZnO/Ag interface (right). c Normalized ToF-SIMS profiles of [Ag+Cs]+ (gray solid curves), [Zn+Cs]+ (gray dashed curves) and [C2H3O2 + Cs2]+ (red solid curves) at the ZnO/Ag interface of the pristine device (top) or the aged device (bottom). The acetates spread into the Ag (red arrow, bottom) after efficiency elevation. d XPS core-level spectra for Ag 3d (left) and Zn 2p (right) at different depths in the device. The corresponding etching times before acquiring the XPS spectra are labeled. e Relative atomic numbers of Ag and Zn extracted from the peak areas of the XPS spectra. f Depth evolutions of the O 1 s spectra at the ZnO/Ag interface, which are normalized according to the atomic numbers of Zn (e top) at the corresponding depths. The binding energies for the lattice oxygen (OI) and the surface oxygen species (OII) are denoted by dashed lines. g Normalized atomic ratios of OI:Zn (red solid circles) and OII:Zn (red hollow circles) at the ZnO/Ag interface.
