Thinner, cheaper photovoltaics
Solar cells based on expensive single-crystal silicon (Si) wafers account for the majority of devices sold today. Thin-film Si solar cells significantly reduce costs, but their efficiency is the same or lower than average. New technologies currently in the pipeline will be much more efficient but with lower costs to encourage widespread market uptake. The objective of the PHOTONVOLTAICS (Nanophotonics for ultra-thin crystalline silicon photovoltaics) project was to enable the development of a new solar cell technology. It included nano-texturing, which is expected to increase optical properties above current limits. Different lithography technologies, nanoimprint, hole-mask colloidal and laser interference lithographies, were assessed for their ability to integrate the special nanopatterns with crystalline silicon (c-Si) photovoltaics. Significantly less Si was required, thereby reducing costs, with the lithography techniques being chosen for their low-cost potential. As a high-risk Future Emerging Technologies project, PHOTONVOLTAICS set itself ambitious goals. Scientist aimed to prove that nano-scale patterning surpasses standard random texturing, thus enabling light absorption to surpass generally accepted limits. At the same time, researchers sought the highest short-circuit current enhancement ever with c-Si technology at a thickness less than 40 μm. This required going beyond a mere improvement of light absorption by c-Si and to electrically convert this light into an effective current into the cell, without damaging its electrical properties. The project has led to the development of a set of powerful tools for modelling realistic solar cells with a very broad range of patterns. It also set out guidelines for the efficient integration of nanophotonic textures into thin-film c-Si solar cells. This technique was demonstrated by the development of ultra-thin cells with boosted short-circuit current densities, without any losses in their electrical properties. This resulted in more than doubled energy conversion efficiency. In addition, researchers assessed the optical and electrical properties of a variety of nanopatterns produced using the three different lithography techniques. The results enabled scientists to identify the most promising conditions for cell integration. PHOTONVOLTAICS outcomes will enable the EU to become a global leader in innovative technologies both for energy and low-cost patterned surfaces in general.
Keywords
Photovoltaics, solar cell, light-trapping, silicon, thin-film, PHOTONVOLTAICS, lithography
