Field-effect mobilities in spin-cast and vacuum-deposited PPV-type pentamers

Field-effect transistors (FET) have been fabricated to determine the hole m obility of spin-cast films of the five-ring PPV-type oligomer 2,5-di-n-octy loxy-1,4-bis((4 ' ,4 " -bisstyryl)styrylbenzene) (Ooct-OPV5). The influence of annealing of the organic layer on the device characteristics and the de rived mobility is investigated. In all cases a reasonable saturation of the drain-source hole current is obtained under negative gate bias. Mobilities in the order of 10(-5) cm(2)/V s were calculated from square-law theory. T he reported increase of mobility upon heat treatment is explained by the in crease of the size of the crystalline domains in the organic layer, observe d with polarized light microscopy. The oligomer/gold electrode interfaces a re studied with AFM. Vacuum-deposited films of the five-ring PPV-type oligomer 2-methoxy-5-(2 ' -ethylhexyloxy)-1,4-bis((4 ' ,4 " -bisstyryl)styrylbenzene) (MEH-OPV5) have also been used as semiconducting layers in FETs. Field-effect mobility val ues up to at least one order of magnitude larger than those found for the s pin-cast films are demonstrated. (C) 2001 Elsevier Science B.V. All rights reserved.