High-Performance Solution-Processed Single-Junction Polymer Solar Cell Achievable by Post-Treatment of PEDOT:PSS Layer with Water-Containing Methanol

PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) is widely used as the hole-transporting layer for fabrication of new-generation solar cells. Herein, we utilize water containing methanol to post-treat the PEDOT:PSS surface, by which the insulating PSS component is partially washed out with the PEDOT-to-PSS weight ratio increasing from 1:6.79 to 1:2.93. As a result, the surface becomes more covered with the electrically conductive PEDOT nanodomains, and again the mean current of the conductive nanodomains increases slightly from 6.68 to 7.28 pA, as demonstrated with conductive atomic force microscopy images. The electrical conductivity of the bulk PEDOT:PSS layer increases from 5.51 x 10(-4) to 4.04 x 10(-2) S/cm. The improvement in the surface conductivity allows for more efficient collection of mobile holes with a bit higher value of the hole mobility (5.56 vs 6.78 x 10(-4) cm(2) V-1 s(-1)). The solution-processed single-junction polymer solar cell fabricated on the treated PEDOT:PSS surface shows a higher mean short-circuit current-density (14.46 vs 16.48 mA cm(-2)) and, hence, a higher mean power conversion efficiency (8.23% vs 9.28%) than that on the untreated surface, as calculated from over 200 cells.