The effect of methanol treatment on the performance of polymer solar cells

Significant performance enhancement was observed for the bulk-heterojunction polymer solar cell of ITO/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/poly[N-9 ''-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3' -benzodithiazole)]:[6,6]-phenyl C-71 butyric acid methyl ester (PCDTBT:PC71BM)/Al when the as-cast active layer was rinsed with methanol before the deposition of the metal electrode. Comparison of independent anode interfacial layers of PEDOT: PSS and MoO3 indicated that the effects of methanol treatment on the improvement of device performance are more pronounced for PEDOT: PSS-based devices. No discernible changes can be observed in film thickness, surface topography and UV-vis absorption profiles of the photoactive layer, indicating the absence of film reconstruction and the improvement of device performance are hence attributed to the modification of the interface between the PEDOT: PSS and the fresh active layer. Further examination of the devices containing a cathode interlayer of poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) also demonstrates the potential modification of the interface between the PEDOT: PSS and the active layer by methanol in addition to the widely observed PFN functionality.