The　crystallization　properties　of　the　perylene　(EPPTC)　molecules　doped　in　the　solid　film　of　the　derivative　of　polyfluorene　(F8BT)　at　different　annealing　temperatures,　as　well　as　the　consequently　induced　spectroscopic　response　of　the　exciplex　emission　in　the　heterojunction　structures,　were　studied　in　the　present　paper.　Experimental　results　showed　that　the　phase　separation　between　the　small　and　the　polymer　molecules　in　the　blend　film　is　enhanced　with　increasing　the　annealing　temperature,　which　leads　to　the　crystallization　of　the　EPPTC　molecules　due　to　the　strong　pi-pi　stacking.　The　size　of　the　crystal　phase　increases　with　increasing　the　annealing　temperature.　However,　this　process　weakens　the　mechanisms　of　the　heterojunction　configuration,　thus,　the　total　interfacial　area　between　the　small　and　the　polymer　molecules　and　the　amount　of　exciplex　are　reduced　significantly　in　the　blend　film.　Meanwhile,　the　energy　transfer　from　the　polymer　to　the　small　molecules　is　also　reduced.　As　a　result,　the　emission　from　the　exciplex　becomes　weaker　with　increasing　the　annealing　temperature,　whereas　the　stronger　emission　from　the　polymer　molecules　and　from　the　crystal　phase　of　the　small　molecules　can　be　observed.　These　experimental　results　are　very　important　for　understanding　and　tailoring　the　organic　heterojunction　structures.　Furthermore,　this　provides　photophysics　for　improving　the　performance　of　photovoltaic　or　solar　cell　devices.