The use of porous silicon layers in thin‐film silicon solar cells

Abstract

Phone: þ00 32(0)16 281 505, Fax: þ00 32(0) 16 281 501 ** e-mail vdepauw@imec.be, Phone: þ00 32 (0)16 288265 In the quest for lowering the manufacturing cost of silicon solar cells, imec has been working successfully on two crystalline Si 'thin-film' cell concepts. In a first concept, a 20 mm-thin Si solar cell is epitaxially grown on top of a porous Si-based Bragg-type reflector which is electrochemically etched in a low-cost UMG Si substrate. Large area solar cells with efficiencies of 15.2% have been made, using (semi-)industrial processing tools. This clearly demonstrates that this cell concept has almost reached the stage of industrial application. In a second, longer-term approach, a 1-5 mm-thin, stand-alone mono-crystalline film is created based on the controlled annealing of an ordered macroporous silicon layer (the 'Epi-free' process). With this very thin Si layer, a simple proof-of-concept solar cell has been made exhibiting an efficiency of 4%. By optimizing the cell process in terms of light trapping and passivation, efficiencies over 15% can be expected from this technology.

Photonic light trapping and electrical transport in thin-film silicon solar cells

“…The development of high-quality thin-film silicon layers that can serve as PV material for such solar cells based on advanced photonic concepts remains a crucial challenge, which is of great current interest for research in material science. In this regard, it is encouraging that promising steps have been recently reported [4][5][6][7][8] towards this goal.…”

“…Recently, this picture has been changed: progress in the fabrication of thin epi-free c-Si layers [4] and thin multicrystalline Si on glass by liquid-phase recrystallization [5,6] gives the possibility to obtain high-quality thin silicon layers and solar cells with a promising efficiency [7,8]. Moreover, the recent drop in prices of conventional c-Si technologies mitigated the need for a reduction of the active material (and, hence, material costs).…”

Photovoltaic effect with high open circuit voltage observed in electrochemically prepared nanocrystalline silicon membranes

“…While a relatively large amount of studies involving the use of nc-PSi in solar cells as a passive element (anti-reflection coating, layer transfer process, etc.) are available [13][14][15][16][17], only a few reports actually focused on the possible wide gap absorber nature of the material and its application to solar cells as an active element [18]. Nc-PSi relative simplicity of fabrication as well as a strongly established relation between its observed optical properties and band gap widening model make the material a possible candidate for top cell material in next generation solar cells.…”

Optical characterization of selectively transparent and conducting photonic crystals for use in thin crystalline silicon photovoltaics

“…In addition, by having a stop-gap only at some wavelengths, some illumination from the rear will be transmitted through the reflector and to the c-Si absorber layer. Both alternating layers of porous silicon [3] and c-Si/Silica [4] have been used in thin silicon solar cell designs. However, porous silicon Bragg stacks require many layers in order to reflect a significant amount of light.…”