Light emitting vacuum evaporated devices based on triaryldiamine materials and 8-hydroxyquinoline complexes of Al(III) and Zn(II) Gabriele Giro 1 , Massimo Cocchi 1 , Piergiulio Di Marco 1 , Valeria Fattori 1 , Pasquale Dembech 2 , Gaia Fabbri 2 , and Mauro Ghedini 3 1 CNR-FRAE, Area della Ricerca, Via P. Gobetti 101, 40129-Bologna, Italy 2 CNR-ICoCEA, Area della Ricerca, Via P. Gobetti 101, 40129-Bologna, Italy 3 Dipartimento di Chimica, Universita‘ della Calabria,-Cosenza, Italy ABSTRACT Vapor deposited double-layer (DL) organic light emitting diodes (OLEDs) based on the combination of materials belonging to the triaryldiamine family as hole transporting materials (HTM) and metal complexes of 8-hydroxyquinoline as electron transporting materials (ETM) have been characterized. As HTM N,N-bis(diphenyl-4-yl)- N,N-diphenyl-benzidine (NBDB), N,N-(naphthalen-1-yl)-N,N-diphenyl-benzidine (NPB) or N,N-diphenyl-N,N-(3-methylphenyl)-1,1-diphenyl-4,4-diamine (TPD) were used. As ETM tris-(8-hydroxyquinolinate)-Al(III) (Alq 3 ) or bis-(8-hydroxyquinolinate)- Zn(II) (Znq 2 ) were used. The typical cell configuration was: ITO/HTM/ETM/Ca,Ag. A comparison of the electrical and light emitting features between devices constructed with the new molecule NBDB and NPB or TPD was made, with the aim of improving their efficiency and stability. INTRODUCTION The electroluminescence (EL) of organic solids received great attention after the discovery that thin organic films emit efficiently when properly biased [1], due to a possible use of this phenomenon in electronic devices: organic light emitting diodes (OLEDs) and full colour flat panel displays [2,3]. The good performances obtained by Tang and Van Slyke were due to the use of a DL device consisting of TPD and Alq 3 ; this arrangement facilitates carrier injection and balance, and removes the region of carrier recombination away from the metal contacts, thus avoiding the luminescence quenching by the electrodes. When TPD is deposited by vacuum evaporation on a substrate at room temperature, an amorphous layer is formed. Unfortunately TPD tends to crystallise after a few days [4], and even more rapidly when is assembled in a device were voltage is applied as a result of the heating due to the Joule effect. The poor durability of OLEDs constructed with TPD was therefore attributed also to this morphological instability. A possible way to solve this problem is the use of materials that form more stable amorphous layers, with higher T g values, in order to avoid or at least reduce any crystallisation process [5,6]. With the aim to improve OLEDs efficiency and stability, we have synthesised NBDB, a triaryldiamine derivative that was never used before in these devices. NBDB belongs to the family of asymmetric triaryldiamines, that is the amine nitrogen is bound to three different aryl groups. Recently was demonstrated that asymmetric substitution of the triaryldiamines hinders crystallisation, often leading to stable glasses [7]. This paper reports the optical, electrical and electroluminescent properties of OLEDs based on Alq 3 or Znq 2 as ETM, using NBDB as HTM, in comparison with