เจนไฟล์จากข้อมูล SQL เป็น excel แล้ว เลข 0 ข้างหน้าหายทำยังไงให้เลข0ไม่หายครับ

        private void button5_Click(object sender, EventArgs e)//
        {
            try
            {
                Connection.connnectsql2();
                SqlConnection constring = new SqlConnection(Connection.strcon2);
                constring.Open();
                constring.Close();
                DateTime dtt = DateTime.Now;;
                DataTable dt = Connection.executsql2("SELECT * FROM A_file");
                dataGridView1.DataSource = dt;
                GenExcel();
            }
            catch (Exception ex)
            {
                AutoClosingMessageBox.Show(ex.Message, "Error", 2000);
            }

public void GenExcel() {
                    SaveFileDialog sfd = new SaveFileDialog();
                    sfd.Filter = "Excel Documents (*.xls)|*.xls";
                    sfd.FileName = "export.xls";
                    //DateTime.Now.Ticks.ToString();
                    //string strdtrp = "";
                    //strdtrp = dtrp.ToString("ddMM");
                    ToCsV(dataGridView1, @"D:\RP601" + DateTime.Now.ToString("ddMM") + ".xls");
                    AutoClosingMessageBox.Show("Send to Excel", "Success", 2000);
                    dataGridView1.Columns.Clear();
                    dataGridView1.Refresh();
}

        private void ToCsV(DataGridView dGV, string filename)//ฟังชั่นของ excel
        {
            string stOutput = "";
            // Export titles:
            string sHeaders = "";

            for (int j = 0; j < dGV.Columns.Count; j++)
                sHeaders = sHeaders.ToString() + Convert.ToString(dGV.Columns[j].HeaderText) + "\t";
            stOutput += sHeaders + "\r\n";
            // Export data.
            for (int i = 0; i < dGV.RowCount; i++)
            {
                string stLine = "";
                for (int j = 0; j < dGV.Rows[i].Cells.Count; j++)
                    stLine = stLine.ToString() + Convert.ToString(dGV.Rows[i].Cells[j].Value) + "\t";
                stOutput += stLine + "\r\n";
            }
            Encoding utf16 = Encoding.GetEncoding(874);
            byte[] output = utf16.GetBytes(stOutput);
            FileStream fs = new FileStream(filename, FileMode.Create);
            BinaryWriter bw = new BinaryWriter(fs);
            bw.Write(output, 0, output.Length); //write the encoded file
            bw.Flush();
            bw.Close();
            fs.Close();
        }