Donal Bradley

Abstract:

Here we report the fabrication and optical characterization of organic microcavities containing liquid crystalline conjugated polymers (LCCPs)—poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), poly(9,9-dioctylfluorene) (PFO), and poly(9,9-dihexylfluorene-co-bithiophene) (F6T2)—aligned on top of a thin transparent sulfuric dye 1 (SD1) photoalignment layer. We extract the optical constants of the aligned films using variable-angle spectroscopic ellipsometry and fabricate metallic microcavities in which the ultrastrong coupling regime is manifest both for the aligned and nonaligned LCCPs. Transition dipole moment alignment enables a systematic increase in the interaction strength, with unprecedented solid-state Rabi splittings of up to 1.80 eV, the first to reach energies comparable to those in the visible spectrum. With an optical gap of 2.79 eV for F6T2 this gives the highest-to-date organic microcavity coupling ratio, 65%. We also demonstrate that the coupling strength is polarization-dependent with bright polariton photoluminescence for TE polarization parallel to the polymer chains and either no emission or weakly coupled emission from the corresponding TM polarization.

Abstract:

Metal oxide thin-film transistors are increasingly used in the driving backplanes of organic light-emitting diode displays. Commercial devices currently rely on metal oxides processed via physical vapour deposition methods, but the use of solution-based processes could provide a simpler, higher-throughput approach that would be more cost effective. However, creating oxide transistors with high carrier mobility and bias-stable operation using such processes has proved challenging. Here we show that transistors with high electron mobility (50 cm2 V−1 s−1) and operational stability can be fabricated from solution-processed multilayer channels composed of ultrathin layers of indium oxide, zinc oxide nanoparticles, ozone-treated polystyrene and compact zinc oxide. Insertion of the ozone-treated polystyrene interlayer passivates electron traps in the channel and reduces bias-induced instability during continuous transistor operation over a period of 24 h and under a high electric-field flux density (2.1 × 10−6 C cm−2). Furthermore, incorporation of the pre-synthesized aluminium-doped zinc oxide nanoparticles enables controlled n-type doping of the hybrid channels, providing additional control over the operating characteristics of the transistors.