Comparison of thermal and electrical degradation effects in polyfluorenes

Abstract The origin of the low energy photoluminescence (PL) and electroluminescence (EL) peaks emerging upon degradation of highly blue emissive polyfluorenes (PFs) has been intensively debated in literature during the last years and has recently been identified as the emission from an exciton and/or charge trapping on-chain keto defect. In this work we compare several polyfluorenes with respect to their stability against degradation, namely a poly(9,9 dialkylfluorene) with two hexahydrofarnesyl sidebranches (PF 111/12), a slightly branched PF 2/6 with tetrabromospiro(fluorene-9,9′-fluorene) as branch (PF A193) and the same polyfluorene with triphenylamine endcappers (PF A207). The degradation of these polymers upon storage at an elevated temperature in vacuum and in air is compared using PL and infrared (IR) spectroscopy. We find that the stability of the spiro-type PFs is significantly improved compared to the regular PF. Essentially the same trend is observed in operated devices.