the format difference between TXT and RAW result from xlsread function

[DAT, TXT, RAW]=xlsread('blabla')

for example, column A in Excel file is character type ftxt=TXT(:,1); fraw=RAW(:,1);

why the resulting TXT array can be applied with "strfind" function like ans=strfind(ftxt, 'hello') with no problem,

but ans=strfind(fraw, 'hello') will give me the following error: "Cell must be a cell array of character vectors"