Research On Preparation And Properties Of High Gain Organic Photodetector Modified With Amino Acid

Organic photodetectors are widely used in the fields of optical communication,image sensing,environmental detection and biochemical detection due to their low manufacturing cost,simple preparation process,adjustable photoelectric characteristics and flexible substrate preparation.Compared with inorganic photodetectors prepared by crystalline silicon or compound inorganic semiconductor materials of III-V main cluster elements used with epitaxially grown,organic detectors have excellent detection properties in all spectral bands.The high gain detector has the characteristics of large external quantum efficiency and high responsivity,so high gain detectors have become the research hotspot in the field of organic detectors.The traditional high-gain detector works based on the high negative external bias,so the response speed and the ratio of signal and noise can be effected by the applied high negative external bias.The organic photodetector modified with amino acid designed in this thesis maintains high detection rate under the condition of low positive bias,and avoids the negative effects brought by high bias voltage.In this thesis,the ITO cathode was modified by amino acid,which can optimize the matching degree of the energy level.Subsequently,the film formation process of the active layer was optimized.The active layer prepared by spin coating at 1500 rpm for 60 s and then annealing at 110 ? for 1 h of PDPP3 T detector has the best specific detection rate and response speed.Also the high gain organic detector used PBDTT-DPP and PCBM as light absorption layer was prepared with the low-speed spin coating about 450 rpm of the active layer,and the external quantum efficiency is over 2500% at a low positive bias in 1 V,and the responsivity of the device is as high as 8.06 A/W,and the response time keeps only a few microseconds.The linear dynamic range is over 120 d B,which is better than the performance of current inorganic detectors.The device structure and gain principle of the high gain detector were theoretically analyzed.With the applied electric field and raising temperature instead of light respectively,the influence of external conditions on the active layer was analyzed.According to the analysis about the influence on the detector loop current caused by the external bias in the active layer,it is proved that the working principle is similar to the triode amplification circui t,indicating the role of ITO on loop current.By studying the characteristics of the capacitor-voltage and combining the device structure of the high gain detector,the double heterojunctions formed by the capture of electrons within the shallow level trap in donor material is illustrated.The characteristics of the capacitance changing at different temperatures prove that the gain of the device is achieved through the obstacle formed by the space charge limitation region under dark light,then the balance of the barrier region is destroyed under the illumination,so that the external injection charge recombines,causing the loop current to surge,resulting in high gain effect.