Enhancement of luminance characteristics in top-emission organic light emitting diode with Cr/Al/Cr anodes

Abstract

Top-emission organic light-emitting diodes (TEOLEDs) using chromium anode have been fabricated by employing two techniques: direct-current magnetron sputtering and e-beam evaporation. Atomic force microscopy and work function taken on the chromium film surfaces obtained from both techniques revealed that using dc magnetron sputtering is advantageous over e-beam evaporation in terms of surface characteristics particularly when the film is deposited. The anode having a triple-layer structure of Cr/Al/Cr was deposited on a Si wafer. The device structure of the TEOLED was Cr (20nm)/Al (100 nm)/Cr (20nm)/alpha-napthylphenylbiphenyl diamine (NPB) (60nm)/tris(8-hydroxyquinoline) aluminum (Alq(3)) (60nm)/LiF (1 nm)/Al (2 nm)/Ag (20 nm)/NPB (200 nm). The TEOLED containing the Cr layer deposited by dc magnetron sputtering method showed higher luminance and efficiency than that containing the Cr layer deposited by e-beam evaporation. The superior device characteristics of the TEOLED containing the chromium layer deposited by dc magnetron sputtering have been investigated.