You can find this in the 8760-hour output table of the software by going to the following address:
Double click on the selected scenario > Click on the Export at the bottom of the opened page > Save the CSV (excel) file on your system > Open this file and find the "Cell Temperature" column.
I would like to suggest to you to read the paper entitled "PV Cell Temperature/ PV Power Output Relationships Homer Methodology Calculation" (http://ipco-co.com/IJSET/CIER'13-IJSET/ID_244.pdf)