Masamichi Ikai

Highly efficient phosphorescence from organic light-emitting devices with an exciton-block layer

One of the keys to highly efficient phosphorescent emission in organic light-emitting devices is to confine triplet excitons generated within the emitting layer. We employ “starburst” perfluorinated phenylenes (C60F42) as a both hole- and exciton-block layer, and a hole-transport material 4,4′,4″-tri(N-carbazolyl) triphenylamine as a host for the phosphorescent dopant dye in the emitting layer. A maximum external quantum efficiency reaches to 19.2%, and keeps over 15% even at high current densities of 10–20 mA/cm2, providing several times the brightness of fluorescent tubes for lighting. The onset voltage of the electroluminescence is as low as 2.4 V and the peak power efficiency is 70–72 lm/W, promising for low-power display devices.

Light harvesting by a periodic mesoporous organosilica chromophore.

Light aqueduct: Periodic mesoporous organosilica exhibits strong light absorption due to densely packed organic chromophores within the pore walls. Light energy absorbed by 125 biphenyl groups in the pore walls is funneled into a single coumarin 1 molecule in the mesochannels with almost 100% quantum efficiency, and results in significant enhancement of emission from the coumarin 1 dye.

Hole-transporting periodic mesostructured organosilica.

Hole-transporting framework is formed by surfactant-templated sol-gel polycondensation of an electroactive phenylenevinylene-based organosilane precursor. Molecular geometry of the three-armed precursor contributes to both formation of periodic mesostructures and introduction of hole conductivity in the organosilica hybrids. Electroactive organosilicas with mesopores and large surface areas have great potentials for novel photovoltaic and photocatalytic systems.

Synthesis of visible-light-absorptive and hole-transporting periodic mesoporous organosilica thin films for organic solar cells

Periodic mesoporous organosilica (PMO) thin films that possess both visible-light absorption and hole-transporting properties were synthesized from a newly designed 4,7-dithienyl-2,1,3-benzothiadiazole (DTBT)-bridged organosilane precursor using polystyrene-block-poly(ethylene oxide) (PS-b-PEO) as a template. DTBT-based PMO films were successfully obtained from the 100% organosilane precursor without the addition of other alkoxysilanes such as tetraethyoxysilane and by control of the tetrahydrofuran–ethanol solvent ratio and the PS/PEO group ratio in the block copolymer. The PMO films possess connected cage-like mesopores with diameters of ca. 15–20 nm, which could be derived from templating with spherical micelles. The PMO films exhibited absorption in the visible range between 400 and 650 nm and hole-transport mobility in the order of 10−5 cm2 V−1 s−1. We demonstrate that the PMO thin film functions as a p-type layer for organic solar cells by filling an n-type [6,6]-phenyl C61 butyric acid methyl ester into the mesopores.