i need a coder to solve a simple problem

I have a very long string 'ABCDEFGH....' (more than 10000 characters). I need to split this string into a list of all possible substrings that having 4 consecutive characters. e.g. "ABCD", “BCDE", "CDEF"....Finally i need to put this list into excel format for further data analysis. would you please suggest a method that could help me to do the above?