Two of the recent major research topics in optoelectronic devices are discussed: the development of new organic materials (both molecular and polymeric) for the active layer of organic optoelectronic devices (particularly organic light-emitting diodes (OLEDs)), and light management, including light extraction for OLEDs and light trapping for organic solar cells (OSCs). In the first section, recent developments of phosphorescent transition metal complexes for OLEDs in the past 3–4 years are reviewed. The discussion is focused on the development of metal complexes based on iridium, platinum, and a few other transition metals. In the second part, different light-management strategies in the design of OLEDs with improved light extraction, and of OSCs with improved light trapping is discussed.

A new synthetic route to novel ruthenium-containing polymers is reported. [Ru(L)(L′)Cl₂] type complexes (L and L′ = bidentate N^N ligands) with a dibromo-substituted ligand were polymerized by Stille cross-coupling reaction. The subsequent displacement of chloride ligands by thiocyanate was highly effective and the structures of the target polymers were fully characterized. The main chain absorption showed a significantly red-shift upon metal coordination and the metal-to-ligand charge transfer (MLCT) band of the complex enhanced the photon harvesting ability of the polymer. The extent of π-electron delocalization of the ancillary ligands also showed interesting effects on the electronic properties of the polymers. The photosensitizing and bandgap tuning properties of these Ru(II) complexes demonstrated a new avenue to develop new classes of optoelectronic materials.

Low-bandgap rhenium(I) complex with absorption onset at 795 nm in solution was tethered onto π-conjugated polymer. The conjugated copolymer provides solution processability of the metallopolymer, and the pendant allows the low energy-absorbing Re(I) complex units to be evenly distributed on the thin film. The copolymer tethered with low-bandgap rhenium complex was synthesized by Suzuki cross-coupling reaction. The metal-free polymer (poly-1) tethered with functionalized intramolecular charge transfer dye, 2-phenyl-3-pyridin-2-yl-5,7-di-2-thienylthieno[3,4-b]pyrazine, exhibited high molecular weight, good film-forming properties, and excellent solution processability. The pendants of the conjugated polymer possess donor–acceptor characters and broaden the absorption band. These pendants can function as bidentate ligands for metal chelation. The solubilizing groups on the monomers provide good solubility to the polymer even with high content of metal chelation. Upon the complexation with rhenium(I) pentacarbonyl chloride, the absorption spectrum of the resulting metallopolymer was further extended toward the near-infrared region. Photovoltaic performances based on this metallopolymer have been studied. The design approach of these metallopolymers provides synthetic feasibility for coordinating wide range of metal ions on the pendant, and the resulting low-bandgap polymer can be a potential candidate for light harvesting material in solar cell applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2311–2319, 2010

Two conjugated polymers based on poly(phenylenethiophene) and poly (fluorenethiophene) main chain functionalized with pendant trithiocyanato ruthenium terpyridine complexes were synthesized by the Suzuki coupling reaction. The ruthenium complexes can extend the absorption band to longer wavelength and enhance the photosensitivity in this region. The polymers exhibit very broad absorption band spanning from 400 to 750 nm due to the presence of π-conjugated system and the ruthenium complexes. Such enhancement in optical absorption enables the utilization of solar light in the near IR region. By space charge limited current modeling, the hole carrier mobilities of the polymers were calculated to be in the order of 10⁻⁴ cm² V⁻¹ s⁻¹, which greatly facilitate the transport of charges after the separation of excitons. Heterojunction photovoltaic cells with simple structure ITO/polymer/C₆₀/Al were fabricated. Under simulated AM1.5 solar light illumination, the short circuit currents, open circuit voltages, and power conversion efficiencies of the photovoltaic cells were measured to be 1.53–2.58 mA cm⁻², 0.12–0.24 V, and 0.084–0.12%, respectively. Deposition of PEDOT:PSS on ITO surface did not show significant difference in device performance. Plot of incident photon to charge efficiency as the function of wavelength suggests that absorption by both conjugated main chain and ruthenium complex are essential to the photocurrent generation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1305–1317, 2008