Преобразуйте list
в pd.Series
и используйте pd.concat
import pandas as pd
df = pd.DataFrame()
list1=pd.Series(["a","b","c"])
list2=pd.Series(["d","e","f","g"])
df = pd.concat([list1,list2], ignore_index=True, axis=1)
df.to_excel('output.xlsx',index = False)
Выход:
0 1
0 a d
1 b e
2 c f
3 NaN g