Study on the Electrical Conductive Mechanism in the Five-layered Structure of Organic Light-emitting Diodes

Abstract

The Electrical conductive mechanism was studied using a five-layered structure of organic light-emitting diodes. The manufactured device structure was ITO/2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole (AF)/N,N'-diphenyl-N,N'bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine(TPD)/tris(8-hydroxyquinoline)aluminum (Alq(3))/(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/LiF/Al. From the analysis of the current density-luminance-voltage characteristics of the five-layered device, four conductive mechanisms depending on the applied voltage region were found. In the Schottky region, where the electric field E is below 1.6 x 10(5) V/cm, the obtained Schottky coefficient beta(ST) is 3.98 x 10(-24) JV(-1/2)m(1/2). In the negative-resistance region, where the electric field is below 3.7 x 10(5) V/cm, the current density J is proportional to E(-2.41), In the Poole-Frenkel region, where the electric field is below 6.4 x 10(5) V/cm, the obtained Poole-Frenkel coefficient beta(P F) is 7.80 x 10(-24) JV(-1/2)m(1/2). The experiment obtained value of beta(P F) corresponds to 1.96 times that of beta(ST), which is theoretically expected because beta(P F) = 2 beta(ST). In the Folwer-Nordheim region, where the electric field is above 8.30 x 10(5) V/cm, the obtained potential barrier empty set(F N) is 0.42 eV.