Synthesis and memory performance of a conjugated polymer with an integrated fluorene, carbazole and oxadiazole backbone

Abstract

A new soluble conjugated polymer, poly[{9-(4-methoxyphenyl)-9H-carbazole}(9,9-dioctylfluorene)(2,5-diphenyl-1,3,4-oxadiazole)](PCFO), was synthesized through the Suzuki coupling reaction. The absolute fluorescence quantum yield of PCFO was measured using the integrating sphere of a photoluminescence spectrofluorometer, and changed from 49.1% for a dilute tetrahydrofuran solution to 16.2% for a thin film due to the existence of a strong fluorescence quenching effect in the solid state. The HOMO–LUMO bandgap (3.07 eV) calculated from the electrochemical measurement is nearly identical to the optical bandgap (3.06 eV) estimated from the ultraviolet/visible absorption onset data. This film was attached to aluminum and indium–tin oxide contacts to fabricate a memory device with typical bistable electrical switching, nonvolatile write-once read-many-times memory performance, a turn-on voltage of ∼−2.3 V and an ON/OFF ratio of ∼105. Degradation of the current density was observed for neither the ON nor OFF states after one hundred million continuous read cycles, which indicates that both states were insensitive to read cycles. A new soluble conjugated polymer, poly[{9-(4-methoxyphenyl)-9H-carbazole}(9,9-dioctylfluorene)(2,5-diphenyl-1,3,4-oxadiazole)](PCFO), was synthesized and was sucessfully used to fabricate a PCFO-based nonvolatile memory device. This device showed typical bistable electrical switching and nonvolatile write-once read-many-times memory performance, with a turn-on voltage of about −2.3 V and an ON/OFF state current ratio of ∼105.