C# - Prevent Opening Of Application On Browser Refresh?

I have an ASP.NET/C# application that exports some data into an Excel spreadsheet using COM interop at the click of a Button control. When I click the button, Excel is opened with the generated spreadsheet. For what it's worth, here is the button code:

<asp:Button ID="export" Text="Export to spreadsheet" runat="server" OnClick="Export_Workbook" />

This works fine, except when I click the button, close the subsequent spreadsheet, and refresh the page. When the page is refreshed after clicking the button, the call to Export_Workbook() is made again and so the spreadsheet opens again. Firefox, for example, says this when you refresh: "To display this page, Firefox must send information that will repeat any action (such as a search or order confirmation) that was performed earlier." This is something I want to avoid.

I'm sure there's a better way to accomplish what I'm trying to do, I'm just not sure what the best approach is.

Edit

I've accomplished this by doing the following:

protected void Export_Workbook(object sender, EventArgs e)
{
Response.Redirect(Request.Url.AbsolutePath, false);
ItemList.Prepare_Workbook();
}