| Organic photodetectors have the inherent advantages: light weight,solution processing,large-area low-cost fabrication on flexible substrates,and conjugated polymer materials can also control the solubility and band gap width by designing the branched chains,so it is widely used in a variety of industrial and scientific applications,including defense,communications,environmental monitoring,remote sensing control,chemical / biological sensing and aerospace.However,the traditional high-gain organic photodetectors are artificially designed to induce the secondary charge injection by nanoparticles with high density of traps at the surface of the polymer.It is difficult to simultaneously increase the responsivity and the response speed.The preparation process of organic conjugated polymer materials will indispensablly introduce fewer internal traps,while these traps are not enough to produce the gain under the external electric field.In this paper,a high-gain photodetector is fabricated by combining the traps in organic polymer materials with organic-inorganic heterojunctions.Interfacial modification materials can effectively change the interface contact between electrode and active layer to remarkably enhance device performances.In this paper,a simple photodetector based on PCE-10 blended of PC71 BM was fabricated.with amphoteric-ion materials wc-1 and wc-2 modification.The thickness of active layer in this detector device was about 200 nm,and the heat treatment of devices was that active layer was annealed at 110 ? for 20 min after it was spin coated and put for 12 h.Wc-2 at the concentration of 0.75 mg / m L or wc-1 at the concentration of 1.5 mg / m L was spin-coated at the surface of ITO.The external quantum efficiency of the device was increased by more than 12%,the dark current was decreased by an order of magnitude,the detectivity of the device was increased to 1013 Jones,the transient response time was decreased to the level of microsecond and linear dynamic range(LDR)was over 85 d B.The gain of the device is not obvious under the external bias because the internal traps of PCE-10 are too less.According to the result,a simple solution-processed photodetectors based on the PBDTT-DPP with more traps blended of PC71 BM materials were fabrication.The devices showed a large amount of photon to electron multiplication at room temperature with external quantum efficiency(EQE)up to 3500 % under a forward bias of 0.8 V,and the high gain was accompanied with a fast response speed and a high linear dynamic range(LDR).The devices exhibited a normalized detectivity(D*)over 1014 Jones by actual measurements,which was about two to three order of magnitudes higher than the standard silicon detector.The working mechanism of high-gain organic photodetector was that after the contact of the polymer of PBDTT-DPP with the electron-rich Mo O3 layer,electron in the Mo O3 can be traped into the polymer resulting in a space charge region(SCR)one of which is the organic bulk-heterojunction of PBDTT-DPP / PC71 BM and the other is the polymer-inorganic planar heterojunction of PBDTT-DPP / Mo O3.This kind of photocurrent is mainly from the charge injection from external circuit,which is caused by the stimulation of photo-induced carriers.According to this principle,the high-gain photodetector devices will have a fast development if we can control the amount of the trap density of polymer material. |
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