Excel - Change Data Label Font Size

I have the following code in creating an Excel chart in Powershell,  how can I change the Font Size for the Data labels ?

$workbook.ActiveChart.ApplyDataLabels()  turns on the Data Labels,  but how can I change the font ?

    $range = $worksheet1.UsedRange
    $range.EntireColumn.AutoFit()
    $workbook.charts.add()
    $workbook.ActiveChart.chartType= $chartType
    $workbook.ActiveChart.SetSourceData($range)
    $workbook.ActiveChart.ApplyDataLabels()

Thank you for your help