Photocurrent enhancement and photoresponse properties of organic photodetectors with iridium complexes doped in conjugated polymers

Properties of solution-processed organic photodetectors with iridium (Ir) complexes doped in fluorene-type conjugated polymer, poly(dioctylfluorene-co-benzothiadiazole) [F8BT] as a host were investigated. F8BT devices had blue sensitivity. Ir complexes as triplet materials can enhance the incident-photon-to-current conversion efficiency (IPCE) of the devices when their triplet levels are lower than the lowest excited singlet states (S1) of the host and higher than the lowest excited triplet states (T1) of the host. A bilayer F8BT device utilizing solution-processable starburst molecular and tris(2-phenylpyridine)iridium(III) [Ir(ppy)3] as a hole transporting layer and a dopant, respectively, showed larger photocurrent than an non-doped bilayer device under high applied voltage. For the bilayer device with Ir(ppy)3, a cut-off frequency of more than 10 MHz was observed under forward bias of 5 V and clear response pulses at 10 MHz were received using a sinusoidal modulated laser light illumination.