Conjugated polyelectrolyte and zinc oxide stacked structure as an interlayer in highly efficient and stable organic photovoltaic cells

A highly efficient and stable inverted organic photovoltaic cell has been demonstrated by incorporating a zinc oxide (ZnO)/conjugated polyelectrolyte (CPE) stacked structure as an electron-transporting layer. The CPE not only improved the electron collection efficiency in inverted devices but also smoothened the ZnO surfaces, thereby reducing the leakage current and improving the device reliability. In this work, two CPEs, poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) and poly[3-(6-trimethylammoniumhexyl)thiophene] (PTMAHT), are used, and three different interlayers, ZnO, ZnO/PFN, and ZnO/PTMAHT, are systematically studied. By coating PFN onto the ZnO surface, a high power conversion efficiency of 8.54% (with a fill factor of 73%) and similar to 17% efficiency improvement are achieved in thieno[3,4-b]-thiophene/benzodithiophene copolymer, PTB7, and [6,6]-phenyl C-71 butyric acid methyl ester bulk heterojunction solar cells, along with excellent stability.