Abstract
As is common for many conjugated polymers used in light‐emitting diodes (PLEDs), the charge transport in blue‐emitting polyspirobifluorene (PSF) copolymerized with the hole transport unit – N,N,N′N′‐tetraaryldiamino (TAD) biphenyl – is dominated by holes. Although the free electron mobility is an order of magnitude higher than the hole mobility, the electron transport is strongly hindered by traps. By diluting PSF‐TAD with the wide band gap polymer poly(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl) (PFO), the effect of electron trapping can be nearly eliminated. As a result, the transport in the PSF‐TAD:PFO blend becomes electron dominated. Due to the higher electron mobility, PLEDs made from these blends exhibit higher current and light‐output as compared to hole‐dominated PLEDs made from pristine PSF‐TAD. The reduced amount of electron traps enhances their efficiency from 2 cd A−1 for the hole‐dominated PLED to 5.3 cd A−1 for the electron‐dominated blend PLED.
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