One penny collected by fan as contribution (5)
I believe the answer is:
input
'as contribution' is the definition.
(I've seen this before)
'one penny collected by fan' is the wordplay.
'one' becomes 'I' (Roman numeral).
'penny' becomes 'p' (short for pence).
'collected by' means one lot of letters goes inside another.
'fan' becomes 'nut' (both can mean an enthusiast).
'p' inserted within 'nut' is 'nput'.
'i'+'nput'='INPUT'
(Other definitions for input that I've seen before include "Resource" , "data-feed" , "Feed data into a computer" , "Energy" , "Data etc supplied to computer" .)