Blends　and　doping　of　organic　semiconductors　are　generally　employed　to　improve　effectively　the　charge　transfer　and　dissociation　performance.　The　absorption　spectrum　may　be　optimized　making　use　of　the　different　energy　states　of　the　components　in　the　blends,　which　may　favor　the　development　of　the　photovoltaic　or　solar　cell　devices.　Excellent　type-II　heterojunction　structures　can　be　produced　by　mixing　the　small-molecule　perylene　(EPPTC)　and　a　copolymer　of　polyfluorene　(F8BT).　Actually,　F8BT　and　EPPTC　exhibit　absorptions　in　the　blue　region　and　in　the　green　region,　respectively.　Thus,　the　blend　will　have　a　much　broadened　absorption　spectrum.　In　the　experiment,　the　blend　solution　of　these　two　materials　in　chloroform　is　spin-coated　onto　a　piece　of　glass　substrate,　so　that　EPPTC　is　doped　into　the　polymer　of　F8BT　and　the　heterojunction　structure　forms　in　the　final　solid　film.　Then,　steady-state　absorption　and　fluorescence　spectroscopy,　as　well　as　the　transient　photoluminesence　spectroscopy　(time-correlated　single-photon　counting),　is　used　to　investigate　the　formation　and　the　photoluminescence　properties　of　exciplex　in　the　heterojunction　film　of　F8BT　doped　with　EPPTC.　The　photoluminscence　(PL)　spectrum　and　the　life-time　are　measured　to　characterize　the　exciplex　in　the　blend　film,　where　the　longer　life-time　of　the　red-shifted　PL　spectrum　confirms　the　formation　of　the　exciplex.　This　provides　various　experimental　data　for　understanding　the　formation　and　the　photophysical　properties　of　the　heterojunction　structures　in　organic　semiconductor　blends.　Futhermore,　the　absorption　of　the　blend　film　covers　a　large　range　of　the　visible　spectrum.　Therefore,　this　kind　of　doping　of　organic　semiconductor　is　important　for　the　development　of　photovoltaic　and　solar　cell　devices.