On-line monitoring of solar cell module production by ellipsometry technique

摘要

Non-destructive analysing tools are needed at all sudtages of thin film photovoltaic (PV) development, audnd onudproduction lines. In thin film PV, layer thicknesseuds, micro-structure, composition, layer optical propuderties, andudtheir uniformity (because each elementary cell is cudonnected electrically in series within a big panel)udserve as anudimportant starting point in the evaluation of the puderformance of the cell or module. An important focuuds is toudexpress the dielectric functions of each componentudmaterial in terms of a handful of wavelength indepeudndentudparameters whose variation can cover all process vaudriants of that material. With the resulting databasude,udspectroscopic ellipsometry coupled with multilayerudanalysis can be developed for on-line point-by-poinudtudmapping and on-line line-by-line imaging.udThis work tries to review the investigations of difudferent types of PV-layers (anti-reflective coating,udtransparent-conductive oxide (TCO), multi-diode-struducture, absorber and window layers) showing the exiudstinguddielectric function databases for the thin film comudponents of CdTe, CIGS, thin Si, and TCO layers.udOff-line point-by-point mapping can be effective foudr characterization of non-uniformities in full scalude PVudpanels in developing labs but it is slow in the on-udline mode when only 15 points can be obtained (withudin 1 min)udas a 120 cm long panel moves by the mapping stationud. In the last years [M. Fried et al,udThin Solid Filmsud519ud,ud2730 (2011)], instrumentation was developed that prudovides a line image of spectroscopic ellipsometry (udwl=350-ud1000 nm) data. Upto now a single 30 point line imagude can be collected in 10 s over a 15 cm width of PVudmaterial. This year we are building a 30 and a 60 cudm width expanded beam ellipsometer the speed of whiudch willudbe increased by 10X. Then 1800 points can be mappedudin a 1 min traverse of a 60*120 cm PV panel or fleudxibleudroll-to-roll substrate.