Assuntos
Luz , Energia Solar , Alumínio/química , Cristalização , Fótons , Silício/química , Óxido de Zinco/químicaRESUMO
The optical appearance of many flowers in nature relies on their inherent pigments ("chemical color") as well as on the surface structure of the epidermis ("structural color"). The structural color is created by a combination of regular and irregular micro- and nanosized features. With a red rose petal as a biological template, we have separated the structural coloration from the chemical coloration by reproducing the petal's intricate surface structure in a pigment-free polymer. UV-vis reflectance measurements of the templates showed that the pigment-induced chemical coloration of the red-rose petal results in intense absorption and reflection in the green (â¼550 nm) and red (â¼700 nm) spectral region, respectively. The micro- and nanosized structural hierarchy on the petal surface, on the other hand, induced a modulation of the optical reflectivity and a filtering effect in specific wavelength ranges. More notably, we observed that a variation in the size of the micro/nanostructures on the petal surface leads to an effective modulation of the reflectance. These results could provide useful tips for the design of bioinspired optical devices, emulating natural petal structures.
Assuntos
Flores , Pigmentos Biológicos/química , Polímeros/química , Cor , Flores/química , Microscopia Eletrônica de Varredura , Polímeros/análiseRESUMO
We have investigated the impact of three types of intermediate reflectors on the absorption enhancement in the top cell of micromorph tandem solar cells using rigorous diffraction theory. As intermediate reflectors we consider homogenous dielectric thin-films and 1D and 3D photonic crystals. Besides the expected absorption enhancements in cases where photonic band gaps are matched to the absorption edge of the semiconductor, our results distinguish between the impact of zero order Bragg-resonances and diffraction-based enhancement at larger lattice constants of the 3D photonic crystal. Our full-spectrum analysis permits for a quantitative prediction of the photovoltaic conversion efficiency increase of the a-Si:H top cell.
