Device stability and growth of dark spots are major concerns for the large-scale applications of organic light-emitting devices (OLEDs). OLEDs with crystalline hole-transporting layer have been fabricated by depositing organic layers at elevated substrate temperatures. Such devices showed significant improvement in electroluminescent efficiency, morphological stability, storage stability, and also retarded dark-spot growth. The lower hole mobility in crystalline NPB films is attributed to the improved device performance, leading to a better carrier balancing in the NPB/AlQ(3) interface. Such crystalline NPB films also demonstrate a smoother surface, even after high-temperature annealing, and gives beneficial advantages for improving the thermal durability of OLEDs. (C) 2003 Elsevier Science B.V. All rights reserved.