Preparation And Performance Study Of ZnO-based Organic Polymer Multi-color Photodetectors

With the development of optoelectronic devices toward multi-band,high performance and integration,multicolor photodetectors have become a hot research topic in the field of optics and electronic information.Compared with traditional photodetectors,organic-inorganic composite photodetectors can better utilize the advantages of flexibility,light weight and low cost of organic materials,combined with the characteristics of inorganic materials such as high carrier mobility,high stability and high light absorption to achieve high efficiency,high integration and broad spectrum detection of photodetectors.Zinc oxide（ZnO）,a third-generation semiconductor material with high carrier mobility and a large band gap,is one of the preferred materials for photodetectors.Organic polymer materials have tunable structures and simple processes,and the construction of multi-band photodetectors by compounding ZnO and organic polymers has attracted much attention.In this thesis,organic polymer multicolor photodetectors based on ZnO semiconductor films are prepared by combining ZnO with different organic polymers to construct heterogeneous structures,which broaden the response range of the devices and enhance their multi-band detection capability,and also provide a systematic analysis of the working mechanism of the performance improvement.The main research of the paper is as follows:（1）To address the problem of low spectral responsiveness of ZnO UV photodetector,a ZnO/Au/PEDOT:PSS organic polymer UV photodetector was prepared by introducing a p-type polymer PEDOT:PSS as the hole transport layer.The presence of the polymer lowers the trap energy level at the interface,and the photogenerated carriers separate rapidly under the action of the space charge internal displacement electric field,which suppresses the complexation of electron-hole pairs and enhances the photocurrent significantly,with a responsivity of 1.97 A/W at a bias voltage of 9 V,which is more than 70 times higher than that of the ZnO UV photodetector.The EQE of the device is well above 100%at low bias and the response is flat at 280 nm-360 nm.The addition of polymer PEDOT:PSS enhances the response of the ZnO photodetector to the UV region and is accompanied by a high internal gain phenomenon.（2）To address the problem of single detection range of the device,the ZnO/Au/P3HT:PC₆₁BM UV-Vis photodetector was prepared by using the conjugated polymer P3HT as the donor material and PC₆₁BM as the acceptor material and constructing an organic active layer to increase the amount of light absorption.The device increases the absorption of light in the material by the strong absorption coefficient of the organic active layer in the visible range,increases the number of excitons,and expands the spectral response from the UV region to the visible region.The responsiveness is increased by a factor of 10over the ZnO UV photodetector at a bias voltage of 9 V.The presence of the PEDOT:PSS film promotes hole injection and increases the maximum responsivity of the device to 1.47A/W,which is a 4-fold increase in responsivity compared to the ZnO/Au/P3HT:PC₆₁BM device.The response in the UV region is also enhanced.（3）To address the problem of low solar energy spectral utilization,the ZnO/Au/PDPP3T:PC₆₁BM UV-Vis-NIR photodetector was prepared by mixing the conjugated polymer donor PDPP3T and the acceptor PC₆₁BM to build a bulk heterojunction.The PDPP3T molecule has a broad conjugated architecture that absorbs spectra from the UV to NIR range,enabling a UV-Vis-NIR multi-band response.The addition of DIO additives enhances the solubility of the acceptor PC₆₁BM,enhances the ability to receive electrons from the excited state of the donor PDPP3T,promotes charge transport and transfer,and enhances the response of the device in the visible band.Subsequently,using a ternary strategy,a dual-donor/acceptor device was constructed by introducing a donor（P3HT）and an acceptor（IEICO-4F）on top of the binary mixed active layer PDPP3T:PC₆₁BM to adjust the response spectra,and ZnO/Au/PDPP3T:P3HT:PC₆₁BM and ZnO/Au/PDPP3T:IEICO-4F:PC₆₁BM were prepared.PC₆₁BM ternary heterojunction UV-Vis-NIR photodetectors.Compared with the two components,the response of the dual-donor device in the UV-Vis band is significantly enhanced.P3HT can provide enough electrons to the acceptor,increase the separation efficiency of electrons and holes in the device,reduce the compound loss,and the overall EQE of the device is flatter;the response wavelength of the dual-acceptor device is broadened to 1100 nm,and the photocurrent under different light illumination is improved,with a light-dark current ratio of about 3 orders of magnitude,which is Due to the matching of the energy level structure of IEICO-4F with that of PDPP3T:PC₆₁BM,it is conducive to charge separation and transport,and reduces the recombination rate of electrons and holes.