Organic molecular films on gold versus conducting polymer: Influence of injection barrier height and morphology on current–voltage characteristics

The current–voltage characteristics I(V) of model organic devices are studied under ultra-high-vacuum conditions. Active materials are N,N′-bis-(1-naphthyl)-N,N′-diphen-yl1-1,1-biphenyl1-4,4′-diamine (α-NPD) and pentacene, electrode materials are polycrystalline Au and the conductive polymer poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS). Despite a similar work function of electrode material surfaces (∼5 eV), hole injection from PEDOT/PSS is significantly more efficient than from Au, due to a smaller hole injection barrier. Hole injection characteristics from Au electrodes for devices made from α-NPD are independent of deposition sequence and substrate used. Pentacene devices exhibit serious asymmetries in that respect. These are caused by a strong dependence of morphology and preferred molecular orientation on the substrate for the crystalline material.

[1]  K. Seki,et al.  ENERGY LEVEL ALIGNMENT AND INTERFACIAL ELECTRONIC STRUCTURES AT ORGANIC/METAL AND ORGANIC/ORGANIC INTERFACES , 1999 .

[2]  K. Seki,et al.  Energy level alignment at organic/metal interfaces studied by UV photoemission: breakdown of traditional assumption of a common vacuum level at the interface , 1997 .

[3]  T. Jackson,et al.  Pentacene organic thin-film transistors-molecular ordering and mobility , 1997, IEEE Electron Device Letters.

[4]  Antoine Kahn,et al.  Molecular level alignment at organic semiconductor-metal interfaces , 1998 .

[5]  C. Dimitrakopoulos,et al.  Organic Thin Film Transistors for Large Area Electronics , 2002 .

[6]  I. Hill,et al.  Distinguishing between interface dipoles and band bending at metal/tris-(8-hydroxyquinoline) aluminum interfaces , 2000 .

[7]  B. Parkinson,et al.  Direct Observation of a Widely Spaced Periodic Row Structure at the Pentacene/Au(111) Interface Using Scanning Tunneling Microscopy , 2002 .

[8]  T. Tsutsui,et al.  Carrier transport properties of organic materials for EL device operation , 2000 .

[9]  Norbert Koch,et al.  Conjugated organic molecules on metal versus polymer electrodes: Demonstration of a key energy level alignment mechanism , 2003 .

[10]  A. Kahn,et al.  Chemical and electrical properties of interfaces between magnesium and aluminum and tris-(8-hydroxy quinoline) aluminum , 2001 .

[11]  J. Park,et al.  Energy level alignment and two-dimensional structure of pentacene on Au(111) surfaces , 2002 .

[12]  Marie Angelopoulos,et al.  Polymeric anodes for improved polymer light-emitting diode performance , 1997 .

[13]  Friedrich-Karl Bruder,et al.  PEDT/PSS for efficient hole-injection in hybrid organic light-emitting diodes , 2000 .