Reducing the roughness of transparent electrodes in organic photovoltaic devices on plastic substrate by PEDOT:PSS treatment

This work presents our results on surface treatment of flexible polyethelene terephthalate (PET) substrates for fabrication of organic photovoltaic devices (OPVs). The PET substrates coated with transparent electrodes (such as indium oxide, Au and Ag) have a surface roughness with a high amplitude and spatial frequency, resulting in low device yield due to the high chance of short circuit between the top and bottom electrodes. Deposition of a single layer of poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) does not suppress the roughness amplitude and the microscopic images show a non-uniform and defective PEDOT:PSS layer. This work presents a double layer method that reduces the surface roughness drastically, thus improving the yield and uniformity of poly 3-hexylthiophene (P3HT) and [6, 6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) based photovoltaic devices made on PET substrates.