Low-temperature solution-processed flexible organic solar cells with PFN/AgNWs cathode

We report on highly efficient flexible inverted organic solar cells (IOSCs) fabricated by low-temperature solution process on polyethylene terephthalate (PET) substrate. In general, IOSCs have been required to use an annealed (>200 °C) zinc oxide (ZnO) as an electron transport layer. However, any twisting of the flexible substrate during heat treatment leads to poor device performance. To overcome this issue, we developed a novel low temperature process for flexible IOSCs using an alcohol-/water-soluble conjugated polymer, namely poly [(9,9-bis(3′-(N,N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9–dioctylfluorene)] (PFN) instead of the ZnO. Using this low-temperature process, we successfully demonstrate highly efficient flexible IOSCs that are proven to be capable of the power conversion efficiency (PCE) of 6.17% which retain 96% of its efficiency at a bending radius of R≈5 mm or less. To the best of our knowledge, this PCE 6.17% is the best result among the reported values so far for flexible OSCs fabricated on PET substrate.