Interfacial energetics of NaCl–organic composite layer at an OLED anode

Abstract

Although low work function alkaline halides are widely used as a cathode interlayer for organic light-emitting diodes (OLEDs), NaCl-organic composites are shown to be an efficient anodic buffer. Here we suggest a mechanistic origin of the improved OLED performance upon the use of a NaCl-containing organic buffer layer between an indium tin oxide (ITO) anode and N ,N-bis(naphthalene-1-yl)-N ,N-bis(phenyl)benzidine (NPB), based on the studies with ultraviolet photoelectron spectroscopy and atomic force microscopy. While a pure NaCl interlayer has a high hole-injection barrier (1.40 eV), the NPB : NaCl composite layer exhibits a substantially lower barrier (0.84 eV), which is comparable to the value at a bare ITO/NPB interface. Furthermore, the wettability of the composite onto ITO is enhanced due to significant adhesive interactions of NaCl with both ITO and NPB, leading to effective electrical contacts. The two key factors, i.e. the plausible hole-injection barrier and better wettability of the NPB : NaCl composite, contribute to the improved hole injection efficiency and lifetime.

Electronic structures of CuI interlayers in organic electronic devices: An interfacial studies of N,N′ -diphenyl- N,N′ -bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine/CuI and tris-(8-hydroxyquinolinato)aluminum/CuI

“…7a and c, the energy level diagrams of NPB/ITO and Alq 3 /ITO, which were measured in the same manner, are also presented for comparison. The ionization energy (IE) and W of each material are consistent throughout whole measurements and all these values are in a good agreement with previous reports within their error margins [29,30]. Slightly larger IEs of NPB and Alq 3 on the CuI layer might be attributed to the different molecular ordering from those without the CuI layer, which will be discussed later.…”

The utilization of low‐temperature evaporable CsN3‐doped NBphen as an alternative and efficient electron‐injection layer in OLED

“…Thus, the use of special alkali‐metal dispenser makes it difficult in handling and deposition. To overcome this weak point, a variety of alkaline metal salts such as LiF , Li 2 CO 3 , NaCl , or Cs 2 CO 3 had been introduced as n‐type dopant or buffer layer. Even though they are stable during operation, most of these alkali‐metal derivatives possess a very high evaporate temperature.…”