White light emission from an exciplex based on a phosphine oxide type electron transport compound in a bilayer device structure

A white organic light emitting diode (OLED) with a simple structure using exciplex emission is fabricated. The white emission of exciplex is formed at the interface between new electron transport material anthracene-9,10-diylbis(diphenylphosphine oxide) (DPPA) and hole transporting layer N,N'-bis (naphthalen-1-yl)-N,N'-bis(phenyl) benzidine (NPB). Pure white emission with Commission International de L'Eclariage (CIE) coordinates (0.33, 0.33) at the equal-energy white point is obtained. The phosphine oxide type material DPPA based OLEDs work well when Al is directly deposited on them, without an electron injection layer. In order to investigate the mechanism of electron injection from Al to DPPA, Xray photoelectron spectroscopy (XPS) measurements have been carried out and revealed that the improved electron injection is due to the existence of interaction between the phosphine oxide group of DPPA and Al at the DPPA/Al interface.