Morphological and Spectroscopic Studies of Electrochemically Deposited Poly(3,4-ethylenedioxythiophene) (PEDOT) Hole Extraction Layer for Organic Photovoltaic Device (OPVd) Fabrication

Poly(3,4-ethylenedioxythiophene) (PEDOT) was deposited on ITO surface by cyclic voltammetry from mixed toluene/acetonitrile solvent. Thickness and oxidation state of the layer were monitored by UV−vis−NIR spectroscopy and grazing angle FTIR (GA-FTIR) spectroscopy. Morphology had fibrillar character with roughness and porosity dependent on the thickness of the layer. PEDOT was incorporated into organic photovoltaic cell as a hole extraction layer with spin-coated P3HT−PCBM intrinsic layer without further annealing. Performance of the cell was found to be effected by the morphology of the PEDOT layer. A fully doped PEDOT layer of moderate thickness was found to have the highest efficiency demonstrating an open-circuit voltage ( V oc ) of 0.48 V, short-circuit current ( I sc ) of 5.1 mA/cm 2, fill factor (FF) of 0.46, and overall efficiency (ε) of 1.1%. Electrochemically deposited PEDOT was compared to traditional spin-coated PEDOT−PSS of the same thickness. Although V oc and I sc were the same, a 30% improvement in the fill factor was observed for electrochemically deposited PEDOT. The phenomenon was attributed to lower series resistance of the cell due to higher hole mobility of pure PEDOT and better electrical contacts with both the ITO electrode and intrinsic layers.