| Hybrid organic-inorganic halide perovskites(e.g.,CH3NH3PbI3)have attracted considerable attention due to their excellent physical properties,such as large light absorption coefficient,adjustable band gap,small exciton binding energy and long carrier lifetime.At present,it has emerged the most promising semiconductor materials for optoelectronic applications,including solar cells,photodetectors,light-emitting diodes,and lasers.The quality of the perovskite layer plays a critical role in determining the performance of the devices.The preparation of high-quality perovskite films with large grain size,high crystallinity and orientation,and low defect density is the key to fabricate high-performance and high-stability optoelectronic devices.In this thesis,FAxMA1-xPbI3 films were prepared by different methods at first,and then they were used as the "precursor" films.Ater treating these"precursor" films by jointly utilizing the effects of high-temperature,pressure,solvent and space-confinement,high-quality perovskite films were prepared.Finally,optoelectronic devices with high-performance were fabricated.The main contents of this thesis are as follows:1.FAxMA1-xPbI3 precursor film was prepared the by a one-step spin coating method,and the in-situ formation of "visible" ?-FAPbI3 phase within the high-quality MAPbl3 film was realized by a novel pressure-induced phase separation strategy.More importantly,the embedment of highly-resistive ?-FAPbI3 phase can passivate the trap states,suppress the diffusion of cations and increase the intrinsic resistance of MAPbI3 film.Accordingly,on account of long carrier lifetime and low defect density,the MAPbI3/?-FAPbI3 photodetector devices exhibited excellent performance,including high detectivity,responsivity and on/off ratio.Furthermore,the unencapsulated MAPbI3/?-FAPbI3 film device retains over 94%of its initial photocurrent after 15 days in ambient conditions,exhibiting significantly improved stability.2.The dense FAxMA1-xPbI3 polycrystalline film prepared by anti-solvent method exhibits small grain size,poor crystallinity,high-density grain boundaries and rough surface.As a result,the performance of optoelectronic device fabricated from such a polycrystalline film was quite poor.Here we prepared high-quality perovskite film by treating the above FAxMA1-xPb?3 polycrystalline film using a thermal-pressed method.The average grain size of the as-prepared film was as large as 29.5 ?m,and the film was composed of single-crystal in the vertical direction.Besides,the surface of the film was smooth,and the density of grain boundaries and defects were greatly reduced.At the same time,with gentle pressure conditions,a high-quality and uniformly mix-cations FAxMA1-xPbI3 perovskite film was obtained.The photodetector fabricated from such a film exhibited very low dark-current(6×10-11A).When being excited by a 671 nm laser,its on/off ratio was as high as 1.04×106,the responsivity was 3.33 AW-1 and the detectivity is 3.88×1014 Jones.3.The built-in electric field resulted from the ion migration in perovskites greatly affects the performance of perovskite-based solar cells and photodetectors.We investigated the ion migration process within the grain boundary region by using conductive atomic force microscopy(c-AFM).By studying the morphology and the current distribution at the grain boundaryof the thin film prepared by the anti-solvent method and the hot pressing method,we found that secondary-growth process has happened in the polycrystalline perovskite film prepared by anti-solvent strategy under the combined action of temperature and pressure.Thus,grain boundary fusion is realized to reduce the hysteresis of perovskite photovoltaic devices. |
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