Large-area monocrystalline silicon thin films by annealing of macroporous arrays: Understanding and tackling defects in the material

Abstract

A concept that could provide a thin monocrystalline-silicon absorber layer without resorting to the expensive step of epitaxy would be very appealing for reducing the cost of solar cells. The empty-space-in-silicon technique by which thin films of silicon can be formed by reorganization of regular arrays of cylindrical voids at high temperature may be such a concept if the high quality of the thin film could be ensured on centimeter-large areas. While previous works mainly investigated the influence of the porous array on the final structure, this work focuses on the practical aspects of the high-temperature step and its application to large areas. An insight into the defects that may form is given and the origin of these defects is discussed, providing recommendations on how to avoid them. Surface roughening, pitting, formation of holes, and silicon pillars could be attributed to the nonuniform reactions between Si, SiO2, and SiO. Hydrogen atmospheres are therefore preferred for reorganization of macroporous arrays. Argon atmospheres, however, may provide high-quality silicon thin films as well, possibly even more easily transferable, as long as annealing is performed in controlled, clean, and oxygen-free conditions. Our experiments on large areas also highlight the importance of kinetics, which had not been considered up to now and which will require further understanding to ensure a complete reorganization over any wafer area.

Photonic assisted light trapping integrated in ultrathin crystalline silicon solar cells by nanoimprint lithography

“…Technologies that enable the fabrication of thin c-Si layers in the range of 1 μm [2] up to 40 μm [3,4] directly on glass have been proposed. However, c-Si thin-films of a few micrometers suffer from a significantly reduced optical absorption in the red and nearinfrared regions of the solar spectrum.…”

Особенности Процесса Спекания Макропористого Кремния В Атмосфере Аргона

“…Авторы предшествующих работ [1,[15][16][17][18] считали механизм диф-фузии преимущественно поверхностным.…”

“…Следует отметить, что ни в одном из проведенных нами экспериментов не удавалось достигнуть полного заращивания пор на поверхности, т. е. получить безде-фектную корку, как при отжиге в чистом водороде [1,19]. Дефекты в корке представляют собой отверстия, кото-рые происходят от незакрывшихся пор.…”

“…Наиболее подробно сравнение отжигов в H 2 , проводившихся в реакторе для эпитаксиального нара-щивания, с отжигами в Ar в печи с горизонтальной трубой было проведено в работах [1,2]. Однако изучение спекания в этих работах проводилось с точки зрения возможности сформировать полость (SON-структуры) на большой площади и ограничивалось фиксирован-ной температурой.…”

Ultra-thin crystalline silicon films produced by plasma assisted epitaxial growth on silicon wafers and their transfer to foreign substrates

“…Some of the most reliable approaches are: (i) cutting thin wafers and thinning them down by chemical mechanical polishing; (ii) growing thin c-Si films by LPCVD on a seed layer; (iii) annealing macroporous arrays formed on a crystalline silicon wafer (also referred to as silicon on nothing [3,4]); and (iv) the "smart cut" [5][6][7] and ion cutting porcesses [8][9][10][11][12].…”