Morphological Stability of Organic Glasses in LEDs

The crystallization of constituent OLED materials is likely to facilitate most of the extrinsic failure modes. If the cathode conforms to the volume shrinkage in the film that occurs with aging and/or crystallization, uneven charge injection 

FIGURE 3.12. WAXD patterns of Alq3 as it is annealed at 145°C. The initial amorphous hump resolves rapidly into crystalline peaks. 

FIGURE 3.13. DSC of Alq3. Exotherms above and below Tg are due to crystallization. On subsequent scans and following annealing, these peaks disappear. 

It is rare for materials to crystallize rapidly below their glass transition, and the rapid sub-7 crystallization of the Alq3 samples is indicative of the instability of the glassy phase. 

Crystallization of thin Alq3 films could easily be observed with optical microscopy as well. One thousand-angstrom films were fabricated by evaporation and 

---