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Abstract: Improvement in the light extraction efficiency (LEE) of GaN-based green light emitting diodes (LEDs) with ZnO nanostructures synthesized by a hydrothermal method is reported. Formation of ZnO nanorods, hemispheres, and cones was controlled by varying the pH of the aqueous synthesis solution. The shape of the ZnO nanostructures integrated onto the LEDs shows a strong relationship with the LEE characteristics of GaN-based green LEDs. The electroluminescence (EL) intensity of LEDs covered by ZnO nanostructures increased compared to conventional LEDs. In terms of LEE, LEDs with surface-textured ZnO hemispheres showed the highest EL intensity, which can be attributed to an increase in the effective critical angle, the escape cone, and multiple scattering. Finite difference time domain (FDTD) simulation was conducted to theoretically confirm the experimental results. [Copyright &y& Elsevier]

Abstract: Improved optical absorption and photocurrent for polythiophene–fullerene bulk heterojunction photovoltaic devices is demonstrated using a unique self-assembled monolayer of Ag nanoparticles formed from a colloidal solution. With the presence of suitable nanoparticle organic capping groups that inhibit its propensity to agglomerate, the particle-to-particle spacing can be tailored. Transmission electron microscopy reveals the self-assembled Ag nanospheres are highly uniform with an average diameter of ∼4nm and controllable particle-to-particle spacing. The localized surface plasmon resonance peak is ∼465nm with a narrow full width at half maximum (95nm). In the spectral range of 350–650nm, where the organic bulk heterojunction photoactive film absorbs, an enhanced optical absorption is observed due to the increased electric field in the photoactive layer by excited localized surface plasmons within the Ag nanospheres. Under the short-circuit condition, the induced photo-current efficiency (IPCE) measurement demonstrates that the maximum IPCE increased to ∼51.6% at 500nm for the experimental devices with the self-assembled layer of Ag nanoparticles, while the IPCE of the reference devices without the plasmon-active Ag nanoparticles is ∼45.7% at 480nm. For the experimental devices under air mass 1.5 global filtered illuminations with incident intensity of 100mW/cm2, the increased short-circuit current density is observed due to the enhancement of the photogeneration of excitons near the plasmon resonance of the Ag nanoparticles. [Copyright &y& Elsevier]