Organic light-emitting device operational stability at cryogenic temperatures

The operational stability dependence on temperature of an organic light-emitting device (OLED) with a bathocuproine (BCP) blocking layer (BL) is examined. The OLED operated at 20 K has a factor of 5 increase in the operational stability compared to an identical device operated at 300 K. The small increase in stability or decrease in the rate of degradation suggests that the activation energy associated with the degradation process is ≪100 meV. Additionally, the operational stability, at 20 K, of a BL = BCP device is shown to be equivalent to the operational stability of an OLED with an aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq) BL. Given that the glass transition temperature of BCP is lower than BAlq, and that bond cleavage, and intermolecular chemical reactions have >100 meV activation energies, we suggest that the operational instability of BCP BL OLEDs is due to BCPs low glass transition temperature.