OPTICAL PROPERTIES OF MAGNETRON SPUTTERED THIN DIELECTRIC FILMS CONTAINING TERBIUM(III) FOR SPECTRAL CONVERSION IN THIN FILM SOLAR CELLS

摘要

Photovoltaic modules with glass as cover or as superstrate show a poor blue and near UV response due to absorption in the glass and in the doped layer. This poor response of all glass covered solar cells promises an enhancement by spectral conversion of the short wavelength part of the solar spectrum. Thin transparent dielectric films containing Tb~(3+) are developed for this application. These spectral converters with absorption bands between 200 and 400 nm shall be deposited on top of the glass. Their emission bands in the region 400 - 600 nm are well suited for the spectral response of thin film silicon solar cells. Here, the results on the deposition by RF magnetron co-sputtering and characterization of thin SiO_2 and Al_2O_3 films containing Tb~(3+) ions are presented. The highest photoluminescence intensity was found at about 1 at.% Tb in both host materials for as-deposited films. The measured lifetime of the ~5(D_4) - ~7(F_5) (～546 nm) transition was determined to about 1 ms. Annealing studies lead to an enhancement of the photoluminescence intensity by a factor of 2.5 - 3 times.