Rare-earth chelate-doped graded index (GI) polymer optical fibers (POF) are proposed and fabricated. The attenuation loss was measured to be 0.4 dB/m at 650 nm for a GI POF doped with 1 wt % of europium (Eu) chelate. Lifetime shortening and spectral narrowing verified the occurrence of superfluorescence at 614 nm in the Eu chelate-doped GI POF pumped with xenon flashlamps. The demonstration of superfluorescence shows that rare-earth chelate-doped GI POFs are appealing as optical amplifiers and superfluorescent sources in a variety of communication and sensor applications.
We report high-quality dual-junction GaAs solar cells grown using solid-source molecular beam epitaxy and their application to smart stacked III-V//Si quadruple-junction solar cells with a two-terminal configuration for the first time. A high open-circuit voltage of 2.94 eV was obtained in an InGaP/GaAs/GaAs triple-junction top cell that was stacked to a Si bottom cell. The short-circuit current density of a smart stacked InGaP/GaAs/ GaAs//Si solar cell was in good agreement with that estimated from external quantum efficiency measurements. An efficiency of 18.5% with a high open-circuit voltage of 3.3 V was obtained in InGaP/GaAs/GaAs//Si two-terminal solar cells.
Multijunction photovoltaic devices have gained attention for both solar cells and wireless power transmission. Herein, we present the spectral response of each subcell in a monolithic triple-junction photovoltaic device composed of only GaAs subcells with different thicknesses, which clarifies current matching among the GaAs subcells under simulated solar illumination conditions. In addition, the spectral response curves of each subcell show that the power-dependent spectral responses under laser illumination with wavelengths of 405, 660, and 785 nm are explained by the top GaAs subcell, which has a slightly lower shunt resistance and experiences the effects of luminescent coupling.
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