Effect of thermal stability on performance of β-phase poly(9,9-di-n-octylfluorene) in deep blue electroluminescence

The device performances including the emission spectrum and device efficiency of blue-emitting β-phase poly(9,9-di-n-octylfluorene) (β-PFO) annealed at different temperatures from 40 to 160 °C are investigated. The relatively unchanged β-PFO content along with dominating photoluminescence (PL) and electroluminescence (EL) spectra are observed at the thermal annealing temperature (TTA) below 90 °C. As TTA > 90 °C, a gradual decrease in the β-PFO fraction is observed, and there is a significant blue shift of emission spectra at TTA > 130 °C which is due to a generation of large amount of crystalline PFO acting as an energy harvester. As for the device performance, β-PFO can give relatively stable current efficiency and brightness at a temperature between 50 and 80 °C. Based on these results, it suggests that blue-emitting β-PFO is practically applicable in display and illumination as a stable deep-blue light source.