Title :
Crystalline silicon solar cells with doped epitaxial silicon films obtained at low-temperature by PECVD
Author :
Damon-Lacoste, J. ; Labrune, M. ; Granata, S. ; Daineka, D. ; Cabarrocas, P. Roca i
Author_Institution :
Total Gas & Power, Paris La Défense, France
Abstract :
In spite of dramatic improvements in thin film technologies, crystalline silicon (c-Si) solar cells are still leading the photovoltaic market thanks to continuous progress. In this field, one innovative way is the development of thin silicon epitaxial films (epi-Si) on (100) c-Si wafers to fabricate the emitter and/or back surface field of solar cells. Among the possible techniques, we used radio-frequency plasma enhanced chemical vapor deposition (rf-PECVD) for it is a low thermal budget, scalable, wide-spread process in photovoltaics and it is well-suited to make solar cells on thin c-Si wafers (<; 150 μm) without too much stress induced. In this paper, we report the obtaining of n-type epi-Si layers and p-type epi-Si layers by adding a proper amount of phosphine (PH3), diborane (B2H6) or trimethylboron (TMB) to the gas phase as well as appropriately adjusting the deposition temperature, pressure and silane gas flow. For n-type epi-Si layers, we managed to obtain degenerate levels of doping while maintaining the epitaxial growth quality of Si films whereas for p-type we obtained highly doped epi-Si layers with hole concentration spreading from 2.1018 cm-3 to 6.1019 cm-3 (at 300 K). Another noticeable result is that the deposition temperature dependence of the boron-doped epi-Si films changes according to the doping gas used (TMB or B2H6). This behavior has to be opposed to intrinsic epi-Si for which the higher the temperature the better the epitaxy. We also pay a particular attention to reproducibility of doping levels for n-type and p-type epi-Si layers. Finally, we fabricated c-Si solar cells with p-type epi-Si emitter (entirely epitaxial) and a-Si:H back contact (intrinsic and n-type). In this work we compare our previous results based on laser-cutting and screen-printing for which we achieved an efficiency of 14.2 % with a new fully in-house process i- - n which only SF6 etching is used to define the solar cells and evaporated silver contacts are used for the front grid leading to a solar cell efficiency of 13.4 %.
Keywords :
elemental semiconductors; epitaxial layers; plasma CVD; silicon; solar cells; Si; back surface field fabrication; crystalline solar cells; deposition temperature; doping gas; emitter surface field fabrication; laser cutting; n-type epitaxial layers; photovoltaic market; radiofrequency plasma enhanced chemical vapor deposition; rf-PECVD; screen printing; silane gas flow; thermal budget; thin epitaxial films; thin film technologies; Indium tin oxide; Lead;
Conference_Titel :
Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE
Conference_Location :
Honolulu, HI
Print_ISBN :
978-1-4244-5890-5
DOI :
10.1109/PVSC.2010.5614370