Ambient stable large-area flexible organic solar cells using silver grid hybrid with vapor phase polymerized poly (3,4-Ethylenedioxythiophene) cathode

The presence of PSS in solution processed high conducting polymer PEDOT:PSS (PH1000) limits the reliability and lifetime of organic photovoltaic devices due to its acidic and hygroscopic nature. We have developed an alternative PSS-free transparent electrode, based on vapor-phase polymerized (VPP) PEDOT in combination with a current collecting silver grid. The hybrid electrode exhibits a low sheet resistance of 1.6 Omega/square with an excellent bending proof performance. The power conversion efficiency (PCE) is 2.63% in a 1.21 cm(2) area device with a stacking structure of PET/Ag-grid/VPP-PEDOT/ZnO/poly[(9,9-bis(3-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)](PFN)/poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PC61BM)/MoO3/Al. This efficiency is lower than, but comparable to the PCE (3.36%) of a control device with similar structure PET/Ag-grid/PH1000/ZnO/PFN/P3HT:PC61BM/MoO3/Al. A striking advantage using VPP-PEDOT to replace PH1000 is the high ambient stability of the device. The PCE of un-encapsulated devices after 120 h continuous exposure to ambient oxygen and moisture is retained at a 75% level of its initial value. These results suggest that the Ag grid/VPP-PEDOT is a promising alternative to ITO or high conducting PEDOT:PSS for realization of high efficiency, low cost and stable organic solar cells (OSCs). (C) 2015 Elsevier B.V. All rights reserved.