Using a mixed emitting layer of hole and electron transporting molecules to improve the performance of MOLED

Abstract

Performance of the devices is significantly influenced by the charge balance between holes and electrons since the excess of one type over the other would lead to an increase in current but no emission contribution. The device performances were dramatically enhanced by using a mixed emitting layer of NPB and Alq 3 molecules, placed between pure NPB and Alq 3 layer. Comparing with the conventional heterostructure the turn-on voltage was reduced from 7v to 4v and the V--L characteristics was also improved by mixing hole and electron transporting layers. By changing the weight ratio of NPB and Alq 3 the spectrum have 33nm shift and the CIE coordinates have relevant change.