Aluminium introduction in CuInSe2 thin films
by flash evaporation
A. Kachouane, E. Halgand, S. Marsillac, J. C. Bernède*
Université de Nantes, Nantes Atlantique Universités, LAMP, EA 3825, Faculté des Sciences et des Techniques,
2 rue de la Houssinière, BP 92208, Nantes, F-44000 France.
* Corresponding author. E-mail: email@example.com
Received: 31 January 2006; revised version accepted: 14 November 2007
Cu(In1-x,Alx)Se2 (CIAS) thin film absorbers were investigated for photovoltaic cells. Previous studies have shown that the evaporation rate of aluminium has crucial influence on oxygen contamination. In this fact, we have tried to study a new technique for aluminium evaporation. Therefore the Cu(In1-x,Alx)Se2 films were deposited by co-evaporation technique of Cu, In and Se, with a new process to introduce aluminium in CuInSe2 lattice. In that spirit, the “flash technique” has been used for the first time. The composition study by electron probe microanalysis (EPMA) shows that there are only traces of oxygen in the films. We have also studied the aluminium distribution all over the thickness of the films by X-ray photoelectron spectroscopy (XPS) in CIAS. The depth profile shows that aluminium is distributed all over the bulk of Cu(In1-x,Alx)Se2 lattice, however, an aluminium concentration maximum is clearly visible corresponding to the aluminium flash. X-ray diffraction diagrams show that the variation of the lattice spacing varies with Al content. The optical study shows that the band gap of CIAS films increases with increasing aluminium content. However, it seems that Al is only partially active with, possibly, some Al segregation at the grain boundaries mainly in the centre of the film, where Al concentration is maximum.
Keywords: Thin films; Chalcopyrite; solar cell.