Subcell misalignment in vertically cascaded metamaterial absorbers.

Metamaterial has demonstrated exotic electromagnetic (EM) properties and various applications, for example perfect absorbers. Cascaded perfect absorbers further extend the spectral engineering ability. Perfect alignment of subcells was usually presumed in previous studies. We numerically investigated the effect of lateral misalignments existing in the multiple lithography steps for vertically cascaded metamaterial absorbers and found that the position deviations of the subcells play an important role of the spectral response. As an example, near-unity absorbance reduces to only 30% for a λ/10 subcell misalignment. The detailed investigation of EM field and induced current distributions reveals that the relative position variations of strongly coupled subcells contribute to this phenomenon. The results give us an evaluation that how much registration accuracy is required in multi-step lithography for cascaded metamaterials and on the other side a hint of the potential application of this high position sensitivity.

Theoretical design of multi-colored semi-transparent organic solar cells with both efficient color filtering and light harvesting.

Solar cells incorporated with multi-coloring capability not only offer an aesthetic solution to bridge the gap between solar modules and building decorations but also open up the possibility for self-powered colorful display. In this paper, we proposed a multi-colored semi-transparent organic solar cells (TOSCs) design containing metallic nanostructures with the both high color purity and efficiency based on theoretical considerations. By employing guided mode resonance effect, the multi-colored TOSC behave like an efficient color filter that selectively transmits light with the desired wavelengths and generates electricity with light of other wavelengths. Broad range of coloring and luminosity adjusting for the transmission light can be achieved by simply tuning the period and the duty cycle of the metallic nanostructures. Furthermore, accompanying with the efficient color filtering characteristics, the optical absorption of TOSCs was improved due to the marked suppression of transmission loss at the off-resonance wavelengths and the increased light trapping in TOSCs. The mechanisms of the light guiding in photoactive layer and broadband backward scattering from the metallic nanostructures were identified to make an essential contribution to the improved light-harvesting. By enabling efficient color control and high efficiency simultaneously, this approach holds great promise for future versatile photovoltaic energy utilization.

Great light absorption enhancement in a graphene photodetector integrated with a metamaterial perfect absorber.

A novel graphene photodetector with graphene embedded in a metamaterial perfect absorber (MPA) is proposed and its light absorption property is numerically investigated. Absorption above 40% in graphene is obtained, which is over 17 times that of a bare monolayer graphene. Both horizontally and vertically cascaded MPAs integrated with graphene are also investigated.