| The era background of "carbon neutralization" puts forward higher requirements for clean energy.Realizing the effective utilization of solar energy is one of the most promising strategies to solve the current energy crisis.Organic-inorganic composite metal halide perovskite material is becoming the next revolutionary material in the development of renewable energy and photoelectric conversion technology because of its excellent physical properties.Twodimensional Ruddlesden-Popper(RP)perovskite materials have been widely concerned in recent years for their excellent environmental stability.However,high exciton energy and insulating long-chain organic functional groups hinder the generation and transport of carriers in the thin films,which limits the improvement of the performance of thin film devices.Theoretical studies show that the vertical orientation growth and phase control are the key to solve the above problems in two-dimensional RP perovskite films.Oriented growth,controlled synthesis of large n-value phases and gradient arrangement of multi n-value phases all need to realize the transformation from disorder to ordered structure.This process involves the reduction of system entropy,and pressure is an important driving force for the reduction of system entropy.Therefore,based on the "soft" characteristics of perovskite materials,using the designed thermal-pressed(TP)crystal growth method,the following work has been carried out from the aspects of the establishment of thin film orientation growth and phase control method,the development of thin film self-power photodetector and solar cell,and the optimization and enhancement of device performance:(1)Taking PEA2(MA)n-1PbnI3n+1(n=2 and 4)system as an example,two-dimensional perovskite thin films were grown in horizontal(n=2)and vertical(n=4)directions based on the grain fusion growth mechanism under pressure by using the designed TP method.In the film system with small n=2,the vertical uniform TP and spatial confinement function effectively promoted the horizontal crystallization and grain boundary fusion of perovskite materials,and then prepared the horizontally oriented PEA2(MA)n-1PbnI3n+1(n=2)film composed of tens of microns;In the film system of n=4,the disordered polycrystalline particles with small size tend to grow along the vertical direction under pressure.The mechanism of orientation growth of pressure in different n-value systems is deeply understood.The establishment of this method lays a foundation for the subsequent growth of high-quality thin films,device development and performance optimization and enhancement.(2)Based on the above established TP crystal engineering method for oriented growth of two-dimensional RP perovskite films,combined with the additive engineering(NH4SCN)strategy,high-quality PEA2(MA)n-1PbnI3+1(n=5)perovskite films,was grown under optimized TP conditions(150℃&200 MPa),the effect of temperature on the orientation structure of the films was explored,and the mechanism of grain uniaxial orientation growth and controllable synthesis of high purity and large n-value phases under TP effect was deeply understood.Based on the film,a hole-free transport layer self-power photodetector is developed,which shows good photoelectric performance.For example,the spectral responsivity(Rλ)of the optimized thin film devices exceeds 0.2 A W-1 in a wide wavelength range of 400-730 nm;When irradiated by 532 nm laser,the responsivity(R)and detectivity(D*)of the self-power photodetector reach 0.68 AW-1 and 1.28 × 1013jones,with ultra-high switching ratio(1.8 × 108).In addition,when placed in the environment of 30%relative humidity for 30 days,the photocurrent attenuated only 8%,showing good environmental stability.(3)High quality PEA2(MA)n-1PbnI3n+1(n=5)perovskite films were grown on ITO/PEDOT:PSS hole transport layer based on the above cooperative growth strategy and the structural design of trans solar cells.The vertical orientation growth of thin films,controlled synthesis of high content and large n-value phases and vertical quantum well distribution of multi n-value phases are realized.The generation,transport and interface extraction efficiency of carriers in thin film devices are optimized,and the highest power conversion efficiency of solar cells based on this method reaches 15.14%,and different batches of devices have good reproducibility.Through the humidity and light stability test,it is found that the solar cell presents ultra-high environmental stability.(4)High orientation and high purity PEA2(MA)n-1PbnI3n+1(n=5)films were grown on the surface of ITO/PEDOT:PSS by optimizing the TP method,optimizing the appropriate organic cations and optimizing the structural design of the photodetector.On the one hand,the effective removal of grain boundaries in the vertical film is realized,which has the surface characteristics of single crystal like;On the other hand,the high purity and large n-value perovskite grains grow uniformly,and the single crystal runs through the whole thickness direction of the film.The defect density and carrier lifetime of the film have been significantly improved.The Rλ of the self-power photodctector based on the film in the wide wavelength range of 500-700 nm is greater than 0.3 A W-1,and the maximum Rλ is 0.36 A W-1,which is equivalent to the performance of the reported 3D self-power photodetector.In addition,under the irradiation of 532 nm laser,the R and D*are as high as 1.25 A W-1 and 1.95×1013 Jones.After being stored in 40%humidity for 60 days,the performance of the unpacked device is reduced by only 2%,which has ultra-high environmental stability.The device also has an ultra-low detection limit(<31 nW cm-2).Therefore,the self-power photodetector has the advantages of high R and D*,fast response speed,ultra-low detection limit and high environmental stability,and it is expected to have potential application value. |
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