Visualizing the exciton formation channel in exciplex-based organic light-emitting diodes

Employing exciplex to capture the triplet excitons has been proved to be an effective strategy in organic light-emitting diodes (OLEDs). However, the detailed exciton formation pathways in exciplex-based OLEDs are still ambiguous. Here, the spin-dependent exciton formation in exciplex-based OLEDs is visualized by magnetic field effect technique. The results show that when excitons are formed on donor 2,6-bis(3-(9H-carbazol-9-yl)phenyl) pyridine (26DCzPPy) molecules, the magnetic field effect on electroluminescence (MEL) exhibits a hyperfine style line-shape with narrow half-peak width. In contrast, when excitons are directly formed on the donor-acceptor (D-A) interface in the bulk heterojunction, the MEL exhibits a Delta g style line-shape with broad half-peak width. The line-shape of MEL could be an indicator of exciton formation mechanism. Our findings bring a new method to monitor the exciton formation pathways, which offer an opportunity for linking the exciton formation to device efficiency.