A Lithium Carboxylate Ultrathin Film on an Aluminum Cathode for Enhanced Electron Injection in Organic Electroluminescent Devices

Abstract

The effects of new insulating materials of lithium fluoride and lithium carboxylates at an aluminum cathodic interface on the performance of organic electroluminescent (EL) devices are described. Three different cathode interface materials are used: lithium salts of fluoride, acetate, and benzoate. We compare the current density–voltage (I–V) and the luminance–voltage (L–V) characteristics of the devices with Al/lithium carboxylates with those of the devices with Al/LiF or an Al cathode. We find that the bilayer cathodes with lithium carboxylates exhibit better device performance than the cathodes with LiF or the Al cathode itselt. In particular, the device with lithium benzoate gives the best performance of all the devices studied. The improvements are attributed to the lowering in work function of the cathode due to lithium metal formation by the higher reactivity of lithium carboxylates than LiF, with hot Al atoms impinging on these insulating materials.

A possible mechanism for enhanced electrofluorescence emission through triplet–triplet annihilation in organic electroluminescent devices

“…16,23 Here, we have to note that we have made a mistake in the calibration of all luminance measurements in our previous reports 16,[23][24][25][26][27] and the correct luminance data should be 1.825 times higher than those reported. These results indicate the possibility of formation of singlet excited state ( 1 Alq 3 *) through T-T annihilation, as shown in Fig.…”

“…In the most of Alq 3 -based EL devices 24,26,27,32,41,42 reported so far, the luminance increased almost linearly with the current. The EL efficiencies of these devices are typically ϳ3 cd A Ϫ1 because of low p of Alq 3 43,44 and are the same as that of the linear part in Fig.…”

“…32 Except indium-tin-oxide ͑ITO͒ surface modification, the device fabrication and measurements for the EL devices with a C 6 H 5 COOLi/Al bilayer cathode were carried out as previously. 24 After cleaning the ITO substrates were immersed for 5 min in dichloromethane solutions containing 1 mM of 4-chlorobenzoyl chloride or 4-chlorophenylphosphonyl dichloride ͑Tokyo Chemical Industry͒. 23 Ϫ• ) and radical cation ͓Alq 3 ϩ• , created by Eq.…”

First-principles molecular dynamics study of Al/Alq3interfaces

“…Tris (8-hydroxyquinoline) aluminum ðAlq 3 Þ is the most famous electron transport and emission materials of OLEDs [1][2][3] and the Alq 3 /metal interfaces have been intensively studied experimentally [4][5][6][7][8][9][10][11][12][13][14][15][16][17] and theoretically [18][19][20][21][22][23][24]. By using ultraviolet photoemission spectroscopy (UPS) and metastable atom electron spectroscopy (MAES), interfacial gap states were observed at Al=Alq 3 interfaces [10,15].…”

Current-voltage behavior in hole-only single-carrier devices with self-assembling dipole molecules on indium tin oxide anodes

“…4,5 For the study of hole injection, the typical hole-only single-layer devices of ITO͑variously treated͒ /TPD/Al were fabricated as previously. 8 The emitting area was defined to be 5 ϫ 5 mm 2 by using a shadow mask. EL characteristics of the singlelayer devices were measured using an Advantest 6145 electrometer with a Topcon BM-3 luminance meter at room temperature under ambient atmosphere.…”