Positive and negative components of magnetoconductance in hole transport limited organic light-emitting diodes

Abstract

Two kinds of devices using N,N′-Di(naphthalen-1-yl)-N,N′-diphenyl-benzidine (NPB) and dye-doped NPB as emitting layer were fabricated to study their magnetoconductance (MC) response. The MC of the NPB devices contains a positive low-field (0<|B|<40 mT) component but a negative high-field (|B|>40 mT) component at low temperatures. Similar MC is presented in the dye-doped NPB devices even at room temperature. Magnetoelectroluminescence results and energy-level diagram indicate that long lifetime triplet excitons and excessive holes are in these devices. All these observations suggest that triplet exciton-hole reaction is responsible for the negative MC while positive MC is assigned to hyperfine mixing of electron-hole pairs.