Blue mixed host organic light emitting devices

The lifetime is one of the main issues in the development of organic light-emitting devices (OLEDs). In this paper, we present a new OLED with an emitting layer (EML) based on a blue mixed-host (MH) structure. Compared to the conventional host-dopant system, the MH structure consists of two different hosts and one-dopant materials. Using the structure with different host ratio and fixed dopant concentration, the Commission International de L'Eclairage (CIE 1931) coordinates will shift from (0.17, 0.32) to (0.15, 0.22). The operating lifetime of optimal device is much improved over the heterostructure OLEDs, which shows the lifetime of approximately 110 h with initial luminance of 10 000 cd/m(2). The luminance reaches 80 370 cd/m(2) at 10 V, which corresponds to a luminous efficiency of 1.8 cd/A. The significant improvement in device lifetime is attributed to the elimination of the heterojunction interface and the prevention to the formation of fluorescence quenchers. These results demonstrate that the MH structure can extend lifetime without significantly changing the EML with common host material. (C) 2003 Elsevier B.V. All rights reserved.