PEDOT:PSS polymeric conducting anode for admittance spectroscopy

The carrier mobilities of two hole transporting organic materials were evaluated by admittance spectroscopy (AS). The materials were 4,4′,4″-tris{N,-(3-methylphenyl)-N-phenylamino}triphenylamine (m-MTDATA) and N,N^′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine (NPB). They were sandwiched in a configuration of anode/organic material/cathode. The anode was either indium-tin-oxide (ITO) or poly(3,4-ethylenedioxythiophene) doped with polystrenesulphonic acid (PEDOT:PSS). It is shown that PEDOT:PSS can, respectively, form Ohmic and quasi-Ohmic contact with m-MTDATA and NPB. Using PEDOT:PSS as the anode, the average hole mobilities of m-MTDATA and NPB were extracted by AS through susceptance analysis. The results are in excellent agreement with those obtained by an independent time-of-flight (TOF) technique. With PEDOT:PSS, the application of AS for characterizing carrier mobilities can be extended to hole transporting organic materials with highest occupied molecular orbital (HOMO) energy levels down to 5.4 eV.