Suppressing the energy transfer in polymer blends films upon addition of a co-solvent

• Diiodooctane promotes a coarsen phase separation in PFO:F8BT blends.
• A quenching of the energy transfer from PFO to F8BT is thereby induced.
• This approach could be important in the fabrication of white LEDs.

Energy transfer in conjugated polymer blends is an important process in optoelectronics, with its efficiency very sensitive to the details of phase separation in films. Modification of the relative composition of the blend has been the usual strategy to tune the energy transfer efficiency. In this letter we report on a new approach to switch-off that process: the use of a co-solvent. In particular, we find that the addition of 1,8-diiodooctane to xylene solutions of poly(9,9-dioctylfluorene): poly(9,9-dioctylfluorene-alt-benzothiadiazole) (PFO:F8BT), blends, 99:1 by weight, suppresses the energy transfer in films. This leads to a change from green light-emitting diodes into whitish emitting diodes. This energy transfer suppression is attributed to a stronger phase segregation, with the concomitant formation of larger domains of the two polymers, thereby increasing the distance between energy donor (PFO) and acceptor (F8BT) sites.

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