Export line chart into excel using ASP.NET

private void ExportToExcel()
    {
        try
        {
            Response.Clear();
            Response.Buffer = true;
            Response.AddHeader("content-disposition", "attachment;filename=OverallReport.xls");
            Response.Charset = "";
            Response.ContentType = "application/vnd.ms-excel";
            using (StringWriter sw = new StringWriter())
            {
                HtmlTextWriter hw = new HtmlTextWriter(sw);

                //To Export all pages
                dgvTrendChart.AllowPaging = false;
                this.SearchOverallList();

                dgvTrendChart.HeaderRow.BackColor = Color.White;
                foreach (TableCell cell in dgvTrendChart.HeaderRow.Cells)
                {
                    cell.BackColor = dgvTrendChart.HeaderStyle.BackColor;
                }

                for (int rowIndex = dgvTrendChart.Rows.Count - 2; rowIndex >= 0; rowIndex--)
                {
                    GridViewRow row = dgvTrendChart.Rows[rowIndex];
                    GridViewRow previousRow = dgvTrendChart.Rows[rowIndex + 1];

                    for (int i = 0; i < row.Cells.Count; i++)
                    {
                        if (i != 3)
                        {
                            if (row.Cells[i].Text == previousRow.Cells[i].Text)
                            {
                                row.Cells[i].RowSpan = previousRow.Cells[i].RowSpan < 2 ? 2 :
                                                       previousRow.Cells[i].RowSpan + 1;
                                previousRow.Cells[i].Visible = false;
                                row.Cells[i].HorizontalAlign = HorizontalAlign.Center;
                                row.Cells[i].VerticalAlign = VerticalAlign.Top;
                            }
                        }
                    }
                }
                dgvTrendChart.RenderControl(hw);

                //style to format numbers to string
                string style = @"<style> .textmode { } </style>";
                Response.Write(style);
                Response.Output.Write(sw.ToString());
                Response.Flush();
                Response.End();
            }
        }
        catch
        {
            //throw new Exception("");
        }
    }