Highly efficient blue fluorescent OLEDs with doped double emitting layers based on p–n heterojunctions

We fabricate a kind of novel efficient blue fluorescent organic light emitting device (OLED) based on p--n heterojunctions composed of hole transporting layer (HTL) N,N^\prime-bis(naphthalen-1-yl)-N,N^\prime-bis(phenyl)-benzidine (NPB) and electron transporting layer (ETL) 4,7-diphnenyl-1,10-phenanthroline (BPhen), into which a new blue material, DNCA (a derivation of N⁶, N⁶, N¹², N¹²-tetrap-tolylchrysene-6,12-diamine), is partially doped simultaneously, and double emitting layers are configured. With a turn-on voltage of 2.6 V at 1 cd/m², this type of OLED presents a maximum luminance efficiency (η_max) of 8.83 cd/A at 5.818 mA/cm² and a maximum luminance of over 40000 cd/m². Meanwhile, the Commission Internationale De L'Eclairage (CIE) coordinates of this device change slightly from (0.13, 0.27) to (0.13, 0.23) as the driving voltage increases from 3 V to 11 V. This improvement in the electroluminescent characteristics is attributed mainly to the ideal p--n heterojunction which can confine and distribute excitons evenly on two sides of the heterojunction interface so as to improve the carrier combination rate and expand the light-emitting region.