Disentangling Bulk and Interface Phenomena in a Molecularly Doped Polymer Semiconductor

Doping the electron-transport polymer poly{[N,N′-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} [P(NDI2OD-T2)] with bulky, strongly reducing metallocene 1,2,3,4,1′,2′,3′,4′-octaphenylrhodocene (OPR) leads to an increased bulk conductivity and a decreased contact resistance. While former arises from low-level n-doping of intrinsic carrier mobility due trap-filling, latter pronounced accumulation dopant molecules at indium tin oxide (ITO) substrate. Electron transfer OPR ITO work function reduction, which pins Fermi level P(NDI2OD-T2) conduction band thus minimizes electron injection barrier The results demonstrate that disentangling effects electrode modification by doping is essential comprehensively understand doped organic semiconductors.