@AkankshaU For above mentioned, If you need to use the SendSimpleEmail activity below mentioned steps to be followed.
Option : Store the Generated Excel file binary file to Data-WorkAttach-File class and pass the attachment Key param(AttachmentKeysToSend) to the SendSimpleEmail activity
The sendSimpleEmail activity helpful for any attachment stored in the workobject the can include while sending a email. For your Scenario, on fly generated attachment and sending a email and its not much helpful.
Please refer ScheduledTaskProcessor agent for above mentioned usecase.