charset utf-8无法处理导出为ex​​cel表

i am try to export excel sheet in in php. all is fine but German character is not working

my header is like :

header("Pragma: public");
header("Expires: 0");
header("Content-Type:application/vnd.ms-excel; charset=utf-8");
header("Content-type:application/x-msexcel; charset=utf-8");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Content-Type: application/force-download");
header("Content-Type: application/octet-stream");
header("Content-Type: application/download");
header("Content-Disposition: attachment;filename=report.xls");
header("Content-Transfer-Encoding: binary ");

in html live page it shows German character n utf8 like ßäöü but when i export as excel then in excel sheet it is like ßäöü why ?