Yii2 How to add parameters to script tag
In your own AssetBundle you can add
public $jsOptions = [
'async' => 'async',
];
If you want to add this to the Yii2 JqueryAsset bundle (or some other bundle) you can add it to the components parts of your config:
'assetManager' => [
'bundles' => [
'yii\web\JqueryAsset' => [
'jsOptions' => [
'async' => 'async'
],
],
],
],