Study Of Multilayered Organic Photodetectors Based On Transfer Printing Technique

In recent years,multilayer organic photodetectors have gained widespread attention and focused research from researchers by virtue of their low noise current,light weight,and adjustable spectral response range,becoming one of the research hotspots in the field of information detection.Currently,multilayer organic photodetectors prepared in the laboratory based on simple wet spin-coating process have achieved performance（detectivity（D*）,resolution）comparable to commercial silicon-based photodetectors,a sign indicating their great potential for commercial application.However,the poor compatibility of the conventional wet spin-coating process with the industrial roll-to-roll process limits the further development of its commercial production,and the film quality becomes difficult to control due to the interactions between the solvents of different functional layers when using the wet method for continuous deposition of multilayer organic films.Therefore,it is particularly important to develop a novel film-forming process that combines high compatibility with roll-to-roll process with the ability to continuously deposit high-quality organic films.Based on this,this thesis proposes to use a novel transfer process to continuously prepare multilayer active layer structure devices and achieve effective suppression of dark currents by constructing vertically phase-separated active layer structures.In this paper,multilayer organic photodetectors were prepared by the conventional dry（PDMS）transfer process and the new wet（water）transfer process,respectively,and the effects of both transfer processes on the performance of organic photodetectors were investigated as follows.1.The effect of the conventional PDMS transfer process on the performance of multilayer organic photodetectors was studied.Aiming at the drawback that the active layer of the organic photodetector has a large dark current due to the contact between the active layer of the bulk heterojunction and the electrodes on both sides at the same time,the multilayer active layer structure device was prepared by the PDMS stamp transfer process without destroying the underlying film,and further,the gradient vertical phase separation structure was constructed in the active layer by adjusting the ratio of the feeder to the acceptor of different layers.Finally,the multilayer organic photodetector prepared by this method has a significantly lower dark current compared with the conventional bulk heterojunction device,and the dark current density decreases by about 2 orders of magnitude under the 1 V reverse bias condition,which effectively improves the device detection performance by about 1 order of magnitude over the detection rate in the 400 to 900 nm band,and reaches a maximum value of 5.91×10¹² Jones at the 810 nm band.2.The effect of a novel water transfer process on the performance of multilayer organic photodetectors was investigated.To solve the problems of complicated technique,low quality of large-area film deposition,and incompatibility with mass production when using PDMS transfer process for sequential deposition of thin films,this work uses the water transfer process without stamps to deposit receptor-rich bulk heterojunction（small molecule-based）thin films on the underlying organic bulk heterojunction films,and achieves the preparation of organic photodetectors with low dark current and high detection rate of bilayer bulk heterojunction active layers.In this thesis,three common organic solvents（CF,CB,o-xy）were used to compare the aqueous transfer process with the solution-based sequential deposition process.The test results show that the water transfer process is not sensitive to solvent selection.The dark current density and specific detection rate of the devices prepared by sequential spin coating process using different solvents showed large differences depending on the solvents.On the contrary,the dark current density of the devices prepared by water transfer using different solvents decreases by about two orders of magnitude compared with the standard bulk heterojunction devices,and the specific detection rate reaches 10¹² Jones in the 400-900 nm band.In summary,the multilayer organic photodetectors prepared by the transfer process can effectively suppress the dark current and improve the detection performance of organic photodetectors.Meanwhile,the use of wet transfer technology improves the compatibility of wet film formation with the conventional roll-to-roll process while ensuring the continuous deposition of high-quality organic films,which provides a simple and effective idea for the commercial mass production of multilayer organic photodetectors.