Use write_string():

use strict;
use warnings;
use Spreadsheet::WriteExcel;

my $workbook  = Spreadsheet::WriteExcel->new('test.xls');
my $worksheet = $workbook->add_worksheet();
my $col       = my $row = 0;
$worksheet->write_string( $row, $col, '801495E40' );
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Edit: My apologies, but just now noticed that runrig already mentioned this.