Mapping exciton quenching in photovoltaic-applicable polymer blends using time-resolved scanning near-field optical microscopy.

We have used time-resolved scanning near-field microscopy to image the fluorescence decay lifetime across a phase-separated blend of the photovoltaic-applicable polymers poly(9,9^′-dioctylfluorene-alt-benzothiadiazole) (F8BT) and poly(9,9^′-dioctylfluorene-alt-bis- N,N^′-(4-butylphenyl)-bis-N,N^′-phenyl-1,4-phenylenediamine) (PFB). We show that the efficiency of local fluorescence quenching is composition dependent, with excitons on F8BT molecules being more effectively quenched when F8BT is trapped at a low concentration in a PFB-rich phase. Despite such presumed differences in charge-carrier generation efficiency, our results demonstrate that charge extraction from F8BT:PFB devices is the most dominant mechanism limiting their operational efficiency. [ABSTRACT FROM AUTHOR]