Amine-Free ZnO Precursor to Suppress Dedoping of PEDOT Electrodes for All-Solution-Processed Flexible Organic Solar Cells

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used solution-processed electrode in organic solar cells with the advantages of high electrical conductivity and high optical transparency. Highly oxidized (doped) states are the origin of its high electrical conductivity. However, PEDOT can be readily dedoped by reductive reagents, such as amines. Traditional sol–gel ZnO precursors (including ethanolamine and zinc acetate in 2-methoxyethanol denoted as ZnOEA) cause dedoping when deposited on top of PEDOT to produce low work function for electron collection. In this work, we report that an amine-free precursor of ZnO (zinc acetate dehydrate in methanol denoted as (ZnO)EA-free) is introduced to replace traditional ZnO precursors, which can suppress the chemical dedoping of PEDOT:PSS films. PEDOT:PSS remains higher optical transmittance and electrical conductivity after coating (ZnO)EA-free than ZnOEA films. All-solution-processed flexible devices with the device structure of PET/PEDOT:PSS/(ZnO)EA-free/PEI/PM6:L8-BO/PEDOT:F/PEDOT:PSS show a power conversion efficiency of 11.9% with an open-circuit voltage of 0.87 V, a short-circuit current of 20.8 mA cm–2, and a fill factor of 0.66.