Enhanced Performance and Stability of Polymer Solar Cells by In Situ Formed AlOx Passivation and Doping

In this paper, aqueous solution-processed zinc oxide (ZnO) layer modified by ultrathin aluminum (Al) layer was applied to act as the electron transport layer for inverted organic solar cells (OSCs). Compared to devices fabricated with pristine ZnO transport layer, applying an ultrathin Al layer (1.2 nm) on ZnO surface simultaneously enhanced the open circuit voltage (V-oc) from 0.54 to 0.60 V, short circuit current density (J(sc)) from 8.82 to 9.73 mA/cm(2), and fill factor (FF) from 0.56 to 0.66, resulting in better device performance from 2.7% to 3.9% based on poly(3-hexylthiophene):phenyl- acid methyl ester (P3HT:PC61BM) blend. A power conversion efficiency (PCE) as high as 8.0% was reached by applying Poly({4,8-bis[(2-ethylhexyl) oxy]benzo [1,2- b:4,5-b'] dithiophene-2,6-diyl}{3-fluoro-2- [ (2-ethylhexy) carbonyl] thieno-[3,4- b]thiophenediyl}) : [6,6]-phenyl-C-71-butyric acid methyl ester (PTB-7:PC71BM) active layer. The V-oc increase was due to the increased build-in potential and the decreased cathode surface work-function. The enhanced J(sc) and FF were due to the significantly increased charge carrier mobility and reduced surface defects. Meanwhile, the device stability was also much enhanced.