Improving the thermal stability of organic light-emitting diodes by using a modified phthalocyanine layer

Remarkable improvement in thermal stability has been demonstrated in an organic light-emitting diode (OLED) using a metal-free phthalocyanine (H2Pc)-doped copper phthalocyanine (CuPc) layer as a hole injection layer. Compared to an OLED using a CuPc layer, approximately twice the lifetime has been achieved in the OLED using the H2Pc-doped CuPc layer at a high temperature of 85 degreesC, operating under a constant current and starting at a luminance of 400 cd/m(2). Atomic force microscopy measurements show that the dopant of H2Pc depresses the crystallization of a CuPc layer. It is suggested that the improved thermal stability of the OLED is attributable to that of the phthalocyanine layer in morphology. (C) 2002 American Institute of Physics.