The Research On High Gain Bulk Heterojunction Organic Photodetector At A Low Driving Voltage

Because of the advantages of light weight,simple fabrication process,low operating voltage and large-area fabrication in low temperature,the organic photodetector has been widely used in sensing,environment monitoring,national defense,and aerospace,etc.The high gain has played an important role in improving the organic photodetector's responsibility and detectivity.At present,the mechanism of the high gain organic photodetector is mainly based on photoconductive model and multiple exciton generation?MEG?,but the photoconductive model's device is working in high voltage or strong electronic field and the multiple exciton generation is hard to achieve in the organic material,so the research of the high gain organic photodetector working in low driving voltage is becoming the hotspot.In this paper,a high-gain photodetector working in low voltage is fabricated in inverse structure by doping the HL2 defect material in organic polymer materials with organic-inorganic heterojunctions.The use of the interfacial modification material can efficiently reduce the energy barrier between the active layer and the electrodes,so we used the amino acid as the cathodic modified material and the MoO₃ as the anodic modified material in order to improve the photo-generated charge transmision and collection.The blend of the PCE-10 and the PCBM was used as the active layer material,and by exploring the optimum doping ratio of the HL2 organic material into active layer material,finally,the external quantum efficiency?EQE?of the fabricated device is up to 2552%at 1.5 V,the device's responsibility is also greatly increased and the device's detectivity?D*?finally break through to 7.08×10¹⁴Jones as a result of the high gain and the dark current reduction,which is even higher than the commercial inorganic photodetector's detectivity.The influence of the doping HL2 organic material on the device's linearity and aging behaviour also has been investigated,the conclusion indicates that the doping HL2 material not only improves the device's EQE,but also has no negative impacts on the other aspects of the device.We also used the MEH-PPV and PDPP3 T to replace the PCE-10,the related devices also appeared the phenomenon of the high gain at a low driving voltage,the result shows that the the method in the paper to promote the high gain effect is feasible for the organic photodetector.In order to investigate the mechanism of the high gain,we researched the device's structure and each functional layer's influence on the high gain device.The working mechanism of high-gain organic photodetector was that after the contact of the organic defect conjunated material with the electron-rich MoO₃ layer,the electron in the MoO₃material can easily be trapped into the polymer and results in a space charge region?SCR?,which is as a form of the planar heterojunction.This kind of photocurrent is mainly from the charge injection from external circuit,which is caused by the stimulation of photo-induced carriers.