Fluorene co-polymers with high efficiency deep-blue electroluminescence

Abstract

Two new deep blue emitting co-polymers are synthesised and exploited in highly-efficient solution-processed polymer light-emitting diodes (PLEDs). A key molecular design feature is selective functionalisation of 9,9-diphenylfluorene to disrupt backbone π-conjugation, thereby promoting luminescence from short emissive domains (λ^EL_max 422 and 401 nm for P1 and P2 devices, respectively). PLEDs using P1 and P2 in the hybrid architecture ITO/PEDOT:PSS/polymer/TPBi/LiF/Al show low turn-on voltages and remarkably high EQE values of η_ext,max 3.3%, L_max of 167 cd m⁻² with CIE_xy coordinates (0.17, 0.10) for P1; and 3.9%, 274 cd m⁻², CIE_xy (0.17, 0.07) for P2. These performances are currently among the best for PLEDs with CIE_y ≤ 0.10.