I have tried to import a python module on a kivy app for android, anyway whenever i add a requirement in buildozer.spec the build fails out putting this:
# Run 'pip install --download-cache=/home/arctia/.buildozer/cache --target=/home/arctia/Scrivania/Kivy/Programs/Domo_Skills/.buildozer/applibs openpyxl'
no such option: --download-cache
# Command failed: pip install --download-cache=/home/arctia/.buildozer/cache --target=/home/arctia/Scrivania/Kivy/Programs/Domo_Skills/.buildozer/applibs openpyxl
# Buildozer failed to execute the last command
Make sure your buildozer and python-for-android are up to date, this is fixed in the master branches. For buildozer, you should be able to get the latest stable release. For python-for-android, delete the .buildozer directory in your build dir and run buildozer again, it should fetch the newest version.