23. Nanocrystalline Silicon and Solar Cells

Thin-film solar cell technology based on nanocrystalline silicon has made a significant progress since the production of the first hydrogenated nanocrystalline silicon (nc-Si:H) solar cell in 1994. Up to date, the highest conversion efficiency of single-junction nc-Si:H thin-film solar cells has reached 11.8%, and further progress is expected. In this chapter, we aim to outline the progress, trends, and major approaches to enhance the nanocrystalline silicon solar cell technology and achieve considerably higher efficiency numbers. Comprising of two parts, this chapter in its first part describes the fundamentals of nanocrystalline silicon properties, typical fabrication methods, and technologies for solar cells as well as recent progress in nc-Si:H fabrications and properties. The second part states the recent advanced technologies for efficiency improvement and provides an overview of the significant achievements, current status, and future prospects of the thin-film solar cells based on nc-Si:H. In particular, the highest reported open-circuit voltage of 608 mV has been demonstrated in a 650-nm-thick single-junction nc-Si:H solar cell by applying amorphous silicon passivation layers at the n/i interface. Besides, the multijunction solar cell technique has significantly contributed to the improvement of the conversion efficiency. In particular, the best triple-junction tandem solar cells reach an initial active-area efficiency of about 16% in the a-Si:H/a-SiGe:H/nc-Si:H structure. Such an impressive success in light management paves the way to the application of nanocrystalline silicon for many vital fields such as novel texture structures, window layers, intermediate reflectors for the improvements of photocurrent density, and conversion efficiency.