This has come up before, see Re: Re: Using Win32::OLE and Excel - Tips and Tricks.

Here is a small working example, using the CP_UTF8 directive, that doesn't require any further conversion after reading in the data in utf8 format:

    #!/usr/bin/perl -w


    use strict;
    use Cwd;
    use Win32::OLE qw(CP_UTF8);
    use Win32::OLE::Const 'Microsoft Excel';


    my $application = Win32::OLE->new("Excel.Application");
    my $workbook    = $application->Workbooks->Add;
    my $worksheet   = $workbook->Worksheets(1);


    # Make Excel handle UTF8.
    $Win32::OLE::CP = CP_UTF8;


    my $file = 'french_utf8.txt';

    open FH, '<:encoding(utf8)', $file  or die "Couldn't open $file: $
+!\n";


    my $row = 1;

    while (<FH>) {
        chomp;
        $worksheet->Cells($row++,1)->{Value} = $_;
    }

    $workbook->SaveAs({
                        FileName   => cwd() . '/test.xls',
                        FileFormat => xlNormal,
                      });
    $workbook->Close;
[download]

Spreadsheet::WriteExcel also handles utf8 text, see the example here.

--
John.