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 cellswith the advantages of high electrical conductivity and high opticaltransparency. Highly oxidized (doped) states are the origin of itshigh electrical conductivity. However, PEDOT can be readily dedopedby reductive reagents, such as amines. Traditional sol-gelZnO precursors (including ethanolamine and zinc acetate in 2-methoxyethanoldenoted as ZnOEA) cause dedoping when deposited on topof PEDOT to produce low work function for electron collection. Inthis work, we report that an amine-free precursor of ZnO (zinc acetatedehydrate in methanol denoted as (ZnO)(EA-free)) isintroduced to replace traditional ZnO precursors, which can suppressthe chemical dedoping of PEDOT:PSS films. PEDOT:PSS remains higheroptical transmittance and electrical conductivity after coating (ZnO)(EA-free) than ZnOEA films. All-solution-processedflexible devices with the device structure of PET/PEDOT:PSS/(ZnO)(EA-free)/PEI/PM6:L8-BO/PEDOT:F/PEDOT:PSS show a powerconversion efficiency of 11.9% with an open-circuit voltage of 0.87V, a short-circuit current of 20.8 mA cm(-2), anda fill factor of 0.66.