How i can add space in Yii2 kartik gridview?

Question

I'm using Yii2 kartik gridview for displaying orders, i need to add CURRENCY field like

AED 10 but now its showing without space like AED10

Here is my code :

 [
        'class' => 'kartik\grid\DataColumn',
        'attribute' => 'sub_total',
        'hAlign' => 'right',
        'vAlign' => 'middle',
        'format' => ['AED', $currency],
        'width' => '12%',
        'pageSummary' => true
    ]

I need space between currency code and price