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

Abstract

Field-effect transistors (FET) have been fabricated to determine the hole mobility of spin-cast films of the five-ring PPV-type oligomer 2,5-di-n-octyloxy-1,4-bis((4′,4″-bisstyryl)styrylbenzene) (Ooct-OPV5). The influence of annealing of the organic layer on the device characteristics and the derived 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 10−5cm2/Vs were calculated from square-law theory. The reported increase of mobility upon heat treatment is explained by the increase of the size of the crystalline domains in the organic layer, observed with polarized light microscopy. The oligomer/gold electrode interfaces are 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 values up to at least one order of magnitude larger than those found for the spin-cast films are demonstrated.