df.to_excel gives TypeError
#### Code Sample, a copy-pastable example if possible

```python
import numpy as np
import pandas as pd
df = pd.read_csv('example')
df.to_excel('Excel_Sample.xlsx',sheet_name='Sheet1')
```
where output of ``df`` is:
```
    a   b   c   d
0   0   1   2   3
1   4   5   6   7
2   8   9  10  11
3  12  13  14  15
```
and file ***example*** is:
```
a,b,c,d
0,1,2,3
4,5,6,7
8,9,10,11
12,13,14,15
```
#### Problem description

The to_excel function of class dataframe must write the dataframe in the specified excel file instead it returns error:
```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.6/dist-packages/pandas/core/generic.py", line 2256, in to_excel
    engine=engine,
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/formats/excel.py", line 742, in write
    writer.save()
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/excel/_openpyxl.py", line 44, in save
    return self.book.save(self.path)
  File "/usr/local/lib/python3.6/dist-packages/openpyxl/workbook/workbook.py", line 408, in save
    save_workbook(self, filename)
  File "/usr/local/lib/python3.6/dist-packages/openpyxl/writer/excel.py", line 293, in save_workbook
    writer.save()
  File "/usr/local/lib/python3.6/dist-packages/openpyxl/writer/excel.py", line 275, in save
    self.write_data()
  File "/usr/local/lib/python3.6/dist-packages/openpyxl/writer/excel.py", line 75, in write_data
    self._write_worksheets()
  File "/usr/local/lib/python3.6/dist-packages/openpyxl/writer/excel.py", line 215, in _write_worksheets
    self.write_worksheet(ws)
  File "/usr/local/lib/python3.6/dist-packages/openpyxl/writer/excel.py", line 200, in write_worksheet
    writer.write()
  File "/usr/local/lib/python3.6/dist-packages/openpyxl/worksheet/_writer.py", line 354, in write
    self.write_top()
  File "/usr/local/lib/python3.6/dist-packages/openpyxl/worksheet/_writer.py", line 98, in write_top
    self.write_properties()
  File "/usr/local/lib/python3.6/dist-packages/openpyxl/worksheet/_writer.py", line 60, in write_properties
    self.xf.send(props.to_tree())
  File "/usr/local/lib/python3.6/dist-packages/openpyxl/worksheet/_writer.py", line 294, in get_stream
    xf.write(el)
  File "src/lxml/serializer.pxi", line 1230, in lxml.etree._IncrementalFileWriter.write
TypeError: got invalid input value of type <class 'xml.etree.ElementTree.Element'>, expected string or Element
```

trying to open written file using ``df = pd.read_excel('Excel_Sample.xlsx',sheet_name='Sheet1')``
returns error:
```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.6/dist-packages/pandas/util/_decorators.py", line 208, in wrapper
    return func(*args, **kwargs)
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/excel/_base.py", line 310, in read_excel
    io = ExcelFile(io, engine=engine)
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/excel/_base.py", line 819, in __init__
    self._reader = self._engines[engine](self._io)
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/excel/_xlrd.py", line 21, in __init__
    super().__init__(filepath_or_buffer)
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/excel/_base.py", line 359, in __init__
    self.book = self.load_workbook(filepath_or_buffer)
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/excel/_xlrd.py", line 36, in load_workbook
    return open_workbook(filepath_or_buffer)
  File "/usr/local/lib/python3.6/dist-packages/xlrd/__init__.py", line 145, in open_workbook
    raise XLRDError('ZIP file contents not a known type of workbook')
xlrd.biffh.XLRDError: ZIP file contents not a known type of workbook
```

#### Expected Output
The excel file should be written correctly with the dataframe's data.

#### Output of ``pd.show_versions()``

<details>


INSTALLED VERSIONS
------------------
commit           : None
python           : 3.6.8.final.0
python-bits      : 64
OS               : Linux
OS-release       : 4.15.0-70-generic
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_IN
LOCALE           : en_IN.ISO8859-1

pandas           : 0.25.3
numpy            : 1.16.3
pytz             : 2018.7
dateutil         : 2.8.0
pip              : 19.3.1
setuptools       : 41.0.1
Cython           : None
pytest           : 3.9.3
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : 4.3.3
html5lib         : 1.0.1
pymysql          : 0.9.3
psycopg2         : None
jinja2           : 2.10.1
IPython          : 7.0.1
pandas_datareader: None
bs4              : 4.8.0
bottleneck       : 1.2.1
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.3.3
matplotlib       : 3.0.3
numexpr          : 2.7.0
odfpy            : None
openpyxl         : 3.0.2
pandas_gbq       : None
pyarrow          : None
pytables         : None
s3fs             : None
scipy            : 1.1.0
sqlalchemy       : 1.3.11
tables           : None
xarray           : None
xlrd             : 1.2.0
xlwt             : None
xlsxwriter       : None

</details>
