Investigating the singlet and triplet exciton recombination zone in organic light emitting diodes: Insights into field dependence, economic material usage and efficiency roll off

Abstract

The optimum extent of the emissive layer (EML) in an organic light emitting diode (OLED) has a critical influence on the device efficiency. It is required to have an optimum thickness of the EML enabling maximum exciton harvesting without sacrificing carriers towards non-recombination current nor allowing an increased device resistance. Herein, the mapping of singlet and triplet exciton diffusion was done in an OLED by the spatial deployment of luminescent probes and studying the corresponding electroluminescence (EL) spectrum. The singlet and triplet emission zones in an EML of 8-hydroxyquinoline aluminum (Alq3), were mapped by inserting a fluorescent probe of 4-(Dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) or a phosphorescent probe of platinum octaethylporphyrin (PtOEP), at different distances from the hole transport layer (HTL)/EML interface. The influence of the electric field on the exciton recombination was also studied.