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

• Published in: Physica status solidi. A, Applications and materials science Applications and materials science, 2011-06, Vol.208 (6), p.1433-1439
• Main Authors: Van Hoeymissen, Jan, Depauw, Valerie, Kuzma-Filipek, Izabela, Van Nieuwenhuysen, Kris, Payo, Maria Recaman, Qiu, Yu, Gordon, Ivan, Poortmans, Jef
• Format: Article
• Language: English
• Subjects: bragg reflector; epifree; layer transfer process; porous silicon; silicon solar cells
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.201000103

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 µm‐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 µm‐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.