A Guide for Realizing Efficient Polymer Light‐Emitting Electrochemical Cells in a Single Active Layer Device Structure

Full Solution Process of a Near-Infrared Light-Emitting Electrochemical Cell Based on Novel Emissive Ruthenium Complexes of 1,10-Phenanthroline-Derived Ligands and a Eutectic Alloy as the Top Electrode

Near-infrared luminescent materials have recently received considerable attention for a large number of applications, including in solid-state lighting, as bioimaging agents, as photovoltaic cells, and in the telecommunication industry. By adding diverse electron-donating or withdrawing groups on ancillary ligands based on benzenethiol-phenanthroline, we synthesized and optoelectronically characterized a series of novel ionic ruthenium complexes, namely RuS, RuSCl, RuSMe, and RuSNH₂, for using in a light-emitting electrochemical cell. The synthesized complexes are intense red emitters in the range of 584-605 nm in solution, which depends on the substitutions of electron donor/acceptor moieties on the ancillary ligands. To find a suitable quantum mechanical approach, benchmark calculations based on time-dependent density functional theory were carried out on these complexes. Our benchmark revealed that the M06-L method has results close to those of the experiment. Furthermore, to gain a deeper insight into electronic transitions, several excitation processes were investigated at the TD-DFT-SMD-MN12-L/gen level. The results showed that in the designed complexes, the dominant transition is between the 4d_Z² electron of Ru (particle) and the π* orbitals of the ancillary ligand (hole). The single-layer devices, including these complexes along with a Ga/In cathode by a facile deposition method without the addition of any electron or hole transport layers, were fabricated and displayed red (678 nm) to near-infrared (701 nm) emission as well as a decrease of turn-on voltage from 3.85 to 3.10 V. In particular, adding a methyl group to the ancillary ligand in the complex RuSNH₂ increases the external quantum efficiency to 0.55%, one of the highest observed values in the ruthenium phenanthroline family. This simple structure of the device lets us develop the practical applications of light-emitting electrochemical cells based on injection and screen-printing methods, which are very promising for the vacuum-free deposition of top electrodes.

Embedded Reverse-Offset Printing of Silver Nanowires and Its Application to Double-Stacked Transparent Electrodes with Microscale Patterns

We propose an embedded reverse-offset printing (EROP) method, which generates silver nanowire (AgNW) transparent electrodes for display applications. The proposed EROP method can solve the two critical issues of microscale pattern formation and surface planarization. The AgNW electrode had a transmittance of 82% at 550 nm, a sheet resistance of 12.2 Ω/sq, and a 3.27 nm smooth surface. We realized the roll-based pattern formation of AgNW on a plastic substrate as small as 10 μm with negligible step differences to facilitate the proposed method. The proposed EROP method also produced a double-stacked AgNW electrode, enabling the simultaneous operation of separately micropatterned devices. To verify the usefulness of EROP, we fabricated an organic light-emitting diode (OLED) device to demonstrate leakage current reduction and efficiency improvement compared with a conventional indium tin oxide (ITO)-based OLED device. The EROP-based OLED showed 38 and 25% higher current efficiencies than an insulator-patterned AgNW OLED and a conventional ITO-based OLED, respectively.