Heat evolution and dissipation in organic light-emitting diodes on flexible polymer substrates.

We investigated the effect of the heat generated in organic light-emitting diodes (OLEDs) on their performance with a focus on the thermo-physical properties of the substrates. OLEDs were fabricated on polyethylene terephthalate (PET), polyimide (PI), and glass substrates, and the instantaneous and time-resolved performances of the OLEDs were compared. The device operation temperature ( T ) was predicted via heat transfer analysis using the finite element method (FEM). The value of T during operation was experimentally measured using an infrared (IR) camera, and the results were compared with the numerically calculated values. The effects of T on the time-resolved electroluminescence (EL) spectra of the OLEDs on the different substrates were also investigated. The experimental results of this study agreed well with the numerical predictions that the T of the OLEDs on the polymers are higher than the T of the OLEDs on glass during operation due to the relatively low thermal diffusivity ( α ) of the polymer substrates used in this study. The results also showed that the performance and reliability of the flexible OLEDs (f-OLED) are highly dependent on the heat extraction capabilities of the substrates; thus, the current density ( J ), luminescence ( L ), voltage ( V ) characteristics, and efficiencies ( η ) over time of the OLEDs on PET and PI are inferior to the OLEDs on the glass substrate. [ABSTRACT FROM AUTHOR]