charset utf-8无法处理导出为ex​​cel表

Question

我尝试在php中导出excel表。一切都很好，但德国人的性格不起作用

我的标题就像：

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 ");

在html实时页面中显示德语字符n utf8，如ßäöü但是当我导出为ex​​cel然后在excel表中，它就像ßäöü为什么？