Try this:
import openpyxl
wb = load_workbook(filename="xxxx.xlsx")
ws = wb.worksheets[0]
ws['A1'] = 1
ws.cell(row=2, column=2).value = 2
This will set Cells A1 and B2 to 1 and 2 respectively (two different ways of setting cell values in a worksheet).
The second method (specifying row and column) is most useful for your situation:
import openpyxl
wb = load_workbook(filename="xxxxx.xlsx")
for ws in wb.worksheets:
for index, row in enumerate(ws.rows, start=1):
print row
x1 = ucr(row[0].value)
ws.cell(row=index, column=2).value = x1