Application of Highly Conductive DMSO-Treated PEDOT:PSS Electrodes to Flexible Organic Solar Cells

In this paper, we report on bulk heterojunction organic solar cells fabricated on highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) electrodes directly deposited on a flexible polyethylene terephthalate (PET) substrate. The PEDOT:PSS layers were deposited using a neutralized (pH similar to 7) solution The sheet resistance of the PEDOT:PSS films became more than two orders of magnitudes smaller after two step treatments of the PEDOT:PSS than that without the treatments. The treatments include 1) spin coating of the neutralized PEDOT:PSS solution containing 5% of dimethyl sulfoxide (DMSO), and 2) dipping the deposited PEDOT:PSS films in pure DMSO for 30 min As a result, a PEDOT:PSS layer on a PET substrate with a sheet resistance of 158.5 Omega/square and optical transmittance of 58.7% at the light wave length of 600 nm was realized. The organic solar cell based on poly [4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] : [6,6]-phenyl-C71-butyric acid methyl ester fabricated on the PEDOT:PSS substrate exhibited power conversion efficiency of 2.51% that was larger than that of a solar cell fabricated on an indium tin oxide (ITO) coated PET substrate with a similar structure. The PEDOT:PSS substrate was confirmed to be much more flexible than the ITO substrate from bending tests, and it showed no degradation in sheet resistance up to the radius of curvature of 3 mm.