Fabrication And Characterization Of Organic Ultraviolet Photodetectors Based On Npb And Tapc Donors

Ultraviolet (UV) photodetectors (PDs) have wide applications in astrophysical analysis, the atmospheric ozone research, environmental pollution monitoring, fire alarm, mineral exploration and mining, health care, as well as military science and other fields. Wide band gap organic UV PDs have much more attractive to scholars, due to the advantages of low manufacturing cost, simple process and ease of production on large area or flexional substrates. However, the detection of deep-UV light has been limited cause the strong absorption in the short wavelength of the incident electrode ITO of organic UV PDs. Moreover, the responsivity and detectivity of organic UV PDs remains to be further improved.In this work, we used common wide band gap organic small molecule semiconductor materials to prepared different structures of organic UV PDs to improve these shortcomings above, based on the incident electrode PEDOT:PSS with good short-wavelength light transmission properties and electrical conductivity. We also developed high-performance deep-UV PDs detector and visible-blind UV PDs. By optimizing structure of the devices to improve the exciton separation, carrier transportation and charge collection of the electrodes, the optical and electrical properties of organic UV PDs were enhanced. The main research works are as follows:1. A double layer heterojunction device and a single layer bulk heterojunction device based on NPB and BND as donor and acceptor materials were prepared to analyze the impact of the interface between donor and acceptor. The photocurrent density of the devices with a different donor and acceptor thickness and exciton separation efficiency of the devices with modification of the interface between donor and acceptor were discussed.2. Combined advantages of double layer heterojunction and bulk heterojunction, we developed the NPB/NPB:BND/BND device by adding a blend layer of NPB and BND between the separate NPB and BND film. The impact of blend thin layer of donor and acceptor to the performance of the device was discussed. The revised organic UV PD was shown a photocurrent density of32.61μA/cm2and a responsivity of30.3mA/W at365nm with-3V bias.3. A high performance NPB/PBD UV PDs was prepared to study the photocurrent density with different thickness of donor and acceptor and the separation efficiency of photoinduced exciton by improved energy level matching between donor and acceptor. The device was shown a responsivity of630mA/W at-3V with350nm light of60mW/cm2light power density, which is better than the results reported in the literature.4. We proposed that using the high conductivity polymer PEDOT:PSS(PH1000) to form a transparent electrode to replace ITO conductive glass as the incident anode, and developed a high-performance quartz/PEDOT:PSS(PH1000)/PEDOT:PSS(P VP4083)/NPB/Bphen/LiF/Al structure deep-UV PD. By adding materials such as DMSO and isopropyl alcohol, the quality of the film and conductive properties of PEDOT:PSS electrode were improved. PEDOT:PSS(P VP4083) improved the holes gathering capabilities and the critical breakdown voltage of the device as a modified material for the anode. The device was shown a photocurrent density of771μA/cm2and a responsivity of502mA/W and a detectivity of2.67×1012cmHz1/2/W at-7.5V with a220nm UV light.5. Due to the TAPC film had no absorption to visible light, we developed the TAPC/Bphen and TAPC/TAPC:Bphen two kinds of visible-blind deep-UV PDs used TAPC to replace NPB as the donor. The devices were shown dark current density of0.024and0.87μA/cm2, photocurrent density of34and56μA/cm2and responsivity of52and75mA/W. The photocurrent density of TAPC/TAPC:Bphen device was better than the TAPC/Bphen device, but the dark current density was reduced so that the signal to noise ratio to be much lower. In order to improve the ability of the electron transport ability of the device to matching the hole transport ability, we prepared a high-performance TAPC/TAPC:Bphen/Bphen:Cs2CO3structure visible-blind deep-UV PD. The dark current density was reduced to0.026μA/cm2, the photocurrent density was increased to106μA/cm2and the responsivity was increased to126mA/W.