var tile_photo = new ol.layer.Tile({
        source: new ol.source.TileWMS({
            attributions: [
                new ol.Attribution({
                    html: '<a href="http://link">TEXT</a>',
                    collapsed:true,
                    tipLabel:'My attribution'
                })
            ],
           ...............

        })
});

source: new ol.source.TileWMS({
            attributions: [
                new ol.Attribution({
                    html: '<a href="http://link">TEXT</a>',
                    options: {
                        collapsible: true,
                        label: 'A',
                        collapsed: true,
                        tipLabel: 'yooo'
                    }
                })
            ],
.........