By Will Soutter
North Carolina State University researchers have developed a novel technique to fabricate ultra-thin-film solar cells without compromising the solar energy absorption capability, thus paving the way to reduce production costs of solar cells.
The active layer (blue line) is sandwiched between layers of dielectric material.
The researchers have reported their technique in a paper titled ‘Dielectric Core-shell Optical Antennas for Strong Solar Absorption Enhancement’ in the online version of Nano Letters. Co-author, Dr. Linyou Cao informed that the researchers fabricated solar cells utilizing a ‘nanoscale sandwich’ design that involves an ultra-thin ‘active’ layer. For instance, the solar cell created by the researchers has a mere 70-nm-thick amorphous silicon active layer when compared to 300-500-nm-thick amorphous silicon active layer of existing commercial thin-film solar cells.
In a solar cell, solar energy is absorbed by this active layer for conversion into chemical fuel or electricity. The new technique can be applied with other solar cell materials, which include copper indium gallium selenide, cadmium telluride, and organic materials, stated Cao. The technique depends mainly on traditional production processes, but creates a totally different end product.
The first step involves the use of typical lithography techniques to form patterns on the substrate, outlining structures composed of transparent, dielectric material with dimensions of 200-300 nm. Then, an ultrathin amorphous silicon active layer is coated over the substrate and the nanostructures, followed by the coating of another dielectric material layer. The presence of dielectric nanostructures below the active layer forms a thin film featuring elevated surfaces that are uniformly spaced throughout the film, resembling crenellations over a medieval castle.
Cao stated that one key feature of this novel technique is the ‘nanoscale sandwich’ design wherein the active layer is sandwiched between two dielectric layers. The nanostructures behave like highly efficient optical antennas that focus the solar energy towards the active layer. This enables the use of a slimmer layer of active material without compromising performance. On the other hand, in the traditional thin-film design, the efficiency of the solar cell gets affected when a thinner active layer is used.