如何使用PHPExcel插入斜杠“\”？

I want insert into slash in cell,for instance

how can I do this use PHPExcel class?

$styleArray = array(
    'borders' => array(
        'diagonal' => array(
            'style' => PHPExcel_Style_Border::BORDER_THICK,
            'color' => array('argb' => 'FFFF0000'),
        ),
        'diagonaldirection' => PHPExcel_Style_Borders::DIAGONAL_DOWN,
    ),
);
$objPHPExcel->getActiveSheet()->getStyle('A1:B2')->applyFromArray($styleArray);

$objPHPExcel->getActiveSheet()->mergeCells('A1:B2');