| Photodetectors are important in many application areas such as civil use,defense,and scientific research.Traditional commercial photodetectors are based on inorganic semiconductors.In recent years,new semiconductor materials,especially organic semiconductors and organic-inorganic halide perovskite have gain great attractions due to their merits such as ease of production and low cost.Applying new materials in photodetectors to extend the application area and reduce cost is one of the hottest issues to date.There are still huge differences between organic photodetectors and their inorganic competitors,especially on external quantum efficiency(EQE),noise level,and response speed.In this research,photodiode type photodetectors based on phosphorescent materials,photomultiplication type photo detectors based on polymer,and organic-inorganic halide perovskite photodetectors with tunable response spectral range were fabricated and their mechanisms were studied.According to the working mechanism of photodiode type organic photodetecors,longer exciton lifetime is beneficial to stronger output current of the photodetector.Photodiode type organic ultraviolet photodetecors were fabricated based on phosphorescent materials as the donor in active layer.Experimental results show that the mixtures of fullerene derivative and phosphorescent materials with longer exciton lifetime have distinct exciton dissociation phenomenon.Because both donor and accepter materials have strong absorption in ultraviolet region,the devices show visible-blind response,which means strong response in ultraviolet region and weak response in visible light region.This can be considered as an advantage of ultraviolet photodetector.The highest EQE of these organic ultraviolet photodetecors is about 40%?Photomultiplication type photodetectors are necessary in applications that need strong output current to overcome the jamming noise.According to the theory that trapped charges can cause band-bending to assist external charge injection through quantum tunneling,a new type of photomultiplication type photodetector based on polymer and fullerene derivatives was designed and fabricated.Charge traps were introduced and EQE of 16800%was observed,when the fullerene derivative doping rate was extremely small(1%).The EQE chould be further increased to 40000%after LiF buffer layer was removed.Optical field and electron distribution simulation results show that EQE spectral shape strongly depends on the trapped charges near the injection interface.Further experiments show that applied field can assist trapped electrons to hop from one trap to another.Continuously hopping process cause the redistribution of trapped electrons.This effect can be observed from transient photocurrent and EQE spectra under different biases and different bias directions.Spectral response range is a key feature which greatly defines the application of a photodetector.The application area of a photodetector can be extended if the spectral response range can be tuned when necessary.A series of photodetectors with tunable response range were designed and fabricated based on perovskite.Response range can be tuned by adjusting the ratio of mixed-halide in two perovskite layers.The point of this new device structure is that one perovskite layer is electrically isolated from the other perovskite active layer,so that the photons absorbed in the first layer have no contribution to photocurrent.Thus,response in shorter wavelength range was suppressed,and rejection ratio of more than 1000 were achieved.To demonstrate this method can be used in multiple applications,narrow band response photodetector with a full width at half maximum of about 28 nm,as well as a set of red,green and blue(RGB)photodetectors with specific response range to match human's eyes were fabricated. |
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