Query Performance - HELP

I'm doing a query , however I'm learning now. Can you improve the performance of this query?

select a.COD_EMPRESA, b.Dat_pagamento
from SAS_EMPRESA a
full outer join SAS_ITEM_PAGO b on (a.COD_PREF_EMPRESA || a.COD_EMPRESA = b.COD_PREF_EMPRESA || b.COD_EMPRESA)
Where a.COD_GRUPO= 'BOT1' and
TO_CHAR(b.Dat_pagamento,'YYYYMM') BETWEEN 201601 AND 201711