Correlation between near infrared-visible absorption, intrinsic local and global sheet resistance of poly(3,4-ethylenedioxy-thiophene) poly(styrene sulfonate) thin films

The ordinary dielectric function of poly(3,4-ethylenedioxy-thiophene) poly(styrene sulfonate) (PEDOT:PSS) thin films was measured using a combination of spectroscopic ellipsometry and photothermal deflection spectroscopy. This method combination allows for a highly sensitive optical characterization of thin films. Hence, even the detection of weak sub-bandgap and intra-band absorptions is enabled. These intraband transitions of free charge carriers were modeled using a Drude-type oscillator to derive an intrinsic resistances for PEDOT:PSS. These optically derived resistances were compared with those determined by a 4-probe measurement setup for two different types of PEDOT:PSS and for varied annealing temperatures. Good agreement between optical and electrical measurements could be obtained for annealing temperatures smaller than 180∘C. Therefore, we conclude that the proposed combination of our two optical methods is well suited to determine electrical resistances of organic layers.