Enhanced inverted organic solar cell performance by post-treatments of solution-processed ZnO buffer layers

Abstract

The effects of post-treatments (150 °C-thermal, humidity, and vacuum) on the cathode buffer layer of aqueous-solution-processed zinc oxide (ZnO) films on the performance of the inverted organic solar cells (OSCs) are investigated, based on poly(3-hexylthiophene)/[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT/PC₆₁BM) as the active layers. The devices with the ZnO buffer layers that underwent thermal and vacuum post-treatments exhibited 17% and 15% increments in the power conversion efficiency (PCE) as compared to that of the cell without post-treatment on the ZnO layer, mainly due to the increases of the short circuit current (J_sc). It was found that the thermal and vacuum post-treatments reduced the defects and increased the electron mobility in the ZnO buffer layers, improving the electron extractions in the inverted OSCs. Both the 150 °C-thermal and vacuum post-treatments are compatible with plastic substrates, showing a potential way to further improve the film properties of the low-temperature processed ZnO buffer layers.