Since you want to open it inside the very window but in new tab, use HTML tag or
target
for the hyperlinks like this
<a href="link" target="_blank">Click me</a>
target="_blank"
specifies that this page would open in the same window, but in a new window.
Remember, ASP.NET controls transform to HTML strings on the server-side and are sent as HTML strings (elements) to the browser. So, whether it is a GridView (table in HTML) or any other control. Once in the browser you will be using the basic HTML ways of doing stuff, and/or JavaScript to handle them. So, using JavaScript won't be a bad idea either. Stuff run on the code block in Web Forms only, where you've specified the
runat="server"
attribute to the element.