Resarch On Photoelectronic Multiplication Type Organic Photodetectors Based On Tri-phase Bulk Heterojunction

Photoelectronic multiplication(PM)is crucial to detect weak optical signals,which is widely used in various important fields including image sensing,video surveillance,and infrared detection.In recent years,PM structure applied to organic photodetectors(OPDs)have emerged as an innovative strategy to further improve the optoelectronic performance of devices.However,there still exists some defects in these reported PM type OPDs,such as the too high working voltage,complex fabrication,and limited material selection.In order to solve the problems above,PM type OPDs based on C60-doped bulk heterojunction(BHJ)are proposed in this paper.The specific work content is as following:(1)Three kinds of PM type OPDs based on bulk heterojunction doped with small ratio C60 are fabricated,in which the active layers are P3HT:PC6iBM:C60,PBDT-TT-F:PC6iBM:C60,P3HT:PBDT-TT-F:PC6iBM:C60,respectively.The working principle of the PM happening in device is systematically analyzed.The experimental results indicate that the dispersed C60 in the active layer can be considered as electron traps,which can capture photogenerated electron.The charge accumulation at the interface of the cathode Al/active layer causes the band bending of P3HT(PBDT-TT-F),thereby triggering hole tunneling injection under illumination at reverse bias.The resulting PM type devices can work at low bias,which benefits from the high exciton dissociation efficiency of bulk heterojunction.For P3HT:PC6iBM:0.2 mg C60 device,its external quantum efficiency(EQE)value arrives to 327.5%at-1 V under 460 nm(0.21 mW·cm-2)illumination.Whereas PBDT-TT-F:PC6iBM:0.2 mg C60 device only exhibits a 139%EQE.These suggests that donor materials with higher HOMO and LUMO energy levels are beneficial for improving the eff-iciency of PM.Finally,2 mg PBDT-TT-F is introduced to P3HT:PC6iBM:0.2 mg C60 active layer through spectral complementation strategy,realizing the full absorption for three primary color.The resulting device not only retains good response to blue and green light(EQE values are 326.3%,153.9%respectively),but obviously enhances the red light response(EQE values increases from 42.4%to 71.0%).(2)In PBDT-TT-F:PC61BM:C60 PM type device,the hole transport ability and exciton dissociation efficiency of blend films are changed by adjusting PC61BM concentration,which causes the change of the collection efficiency of hole injection current for anode.Finally,the regulation of device operating voltage is achieved.As a result,under the adjacent EQE value(?600%),we can choose not only the device operating at small voltage(high PC61BM concentration)but also the one working under large voltage(low PC61BM concentration).The EQE value and responsivity of optimized PBDT-TT-F:PC61BM:C60 device with weight ratio of 6:6:0.2 arrives to 672.3%and 2.49 A·W-1 under illumination of blue light at-3 V bias,respectively.This paper provides an universal method for obtaining OPDs with facile fabrication,highly optoelectronic performance,low and controllable operating voltage.