I wasn't able to get a button that sat in the widget bar to do what you're describing. I wanted to open a help document from there rather than the links bar or the about page. I built a widget that on it's open event opened a new window with the url I wanted, then the widget panel closed itself. You can occasionally see it momentarily if you're watching for it, but it give the behaviour I was looking for.
onOpen: function() {
window.open(this.config.hyperlink);
var theWidgetID = this.id;
require(["jimu/PanelManager"], function(PanelManager) {
console.log(theWidgetID);
var pm = PanelManager.getInstance();
PanelManager.getInstance().closePanel(theWidgetID + "_panel");
});
}