Tuning of metal work function with organic carboxylates and its application in top-emitting electroluminescent devices.
By fine-tuning of work functions and thus the hole-injection properties of Ag and Al anodes, an electroluminescent device was achieved by using various self-assembled monolayers of organic carboxylate on the electrode surfaces. The IR spectra evidenced different binding behaviors of the carboxylates on Ag and Al. A correlation between the change in work function with the effective dipole moment along the surface normal and the currents in the hole-only devices was observed. These self-assembled-monolayer-modified metals were used as anodes in the fabrication of top-emitting organic light-emitting diodes (TOLEDs). The TOLED with the Ag anode modified by the perfluoroalkanoate exhibited a luminous efficiency as high as 18 cdA(-1), superior to that of the Ag2O-based device. With Al as the anode, the highest luminous efficiency was merely 6 cdA(-1) and decayed rapidly. The poorer EL property and performance of Al-based TOLEDs could be attributed to the weaker ionic bindings of carboxylates on Al and the weaker microcavity effect resulting from the inferior reflectivity of Al as compared to Ag.
Cho
Chun-Pei
CP
Institute of Chemistry, Academia Sinica, Taipei, 11529 Taiwan, Republic of China.
Tao
Yu-Tai
YT