Morphology Control Of Perovskite Film For Perovskite Solar Cell

The organic-inorganic hybrid perovskite material has the advantage of high absorption coefficient,long carrier diffusion length,adjustable band gap,and low temperature solution processing,and becomes a popular material for solar cell,electroluminescence and photodetector.However,it is still difficult to prepare large grains and high quality perovskite film,and the research on the crystallization mechanism of perovskite film is still rare.In this paper,the effects of post-treatment of perovskite film and doping of large organic ion halide on the morphology and crystallization of perovskite were studied,the method for preparing high quality perovskite film and the improved film quality on the performance of perovskite solar cells(PVSCs)were discussed.The main research contents of this paper are shown as follows:(1)MASCN solution was used to treat MAPbI3 film to improve film morphology and improve the performance of PVSCs.MASCN solution was used to treat MAPbI3 film,better morphology with large crystal grains about 1 ?m was performed.When the concentration of MASCN solution was 4 mg ml'1,the obtained perovskite film shown a uniform,compactness and large grain morphology with well crystallinity.The post-treatment of MASCN solution can reduce the defects of the perovskite film,and enhance the extract of carriers,and the power conversion efficiency(PCE)of the PVSCs increased from 14.29%to 17.83%,which can also effectively reduce the J-V hysteresis effect.(2)The large-grain 2D/3D composite perovskite film was prepared which can reduce the defects of the film,eliminate the light-soaking effect,and improve the PCE and light stability of the PVSCS.DABr isopropanol solution is used to treat MAPbI3 films and the grains of the perovskite film can secondary growth into large crystals due to DABr induced Ostwald ripen process.A 2D perovskite capping layer was formed on 3D perovskite films and 2D/3D perovskite hybrids(DA2PbIxBr4-x/MAPbI3)are successfully fabricated.The 2D/3D perovskite hybrid films exhibit good crystallization,pinhole-free and good moisture stability.Meanwhile,the large grain size leads to preferable interfacial contact between TiOx and the perovskite layer which eliminate the light soaking effect and enhance light stability.Furthermore,the specific energy level alignment of the 2D capping layer can enhance the extraction of holes and obstructs the diffusion of electrons at the interface between the 3D perovskite active layer and hole transport layer.The performance of the solar cells based on the 2D/3D perovskite hybrids is significantly enhanced.(3)Two-dimensional material additive were used to promote crystal growth and improve film morphology for efficient and stable perovskite solar cells.The effects of several different diethylammonium halide doping on the morphology of MAPbl3 films were compared.It was found that DA halides can significantly increase the grain size of the perovskite film.The difference of halogen ions will also affect the morphology of the final film.Comparing the three halides,DABr can obviously increase the grain size of the perovskite film,and the average grain size reaches 1.45 ?m.XRD results show that DABr doped film own better crystallinity,and DABr can promote the growth of(110)direction of the film.PL spectra and TRPL spectroscopy tests show that the DABr doped film has reduced defects and increased carrier lifetime.In terms of device performance,DAI doped devices can achieve a PCE of 19.05%,while DABr doped devices can achieve a PCE of 19.58%.The tests of the device show that the DABr mixed perovskite film can effectively inhibit the trap-assisted recombination and enhance the charge extraction ability.(4)The crystallization kinetics of different organic ion doped perovskites was studied,and the mechanism of different organic ion doped perovskite precursors to increase the crystal grains of thin films was explained.By studying the dynamic crystallization process of DABr-doped MAPbI3,it is found that the crystallization process of MAPbI3 is random nucleation ring growth,which leads to the crystal grain edge of MAPbI3 film is clear,which is not conducive to crystal fusion.The MAPbI3 perovskite film prepared by one-step solvent method shown no significant grain growth after heat treatment.For DABr doped MAPbI3 precursor,the process is that DABr first forms a crystal nucleus,MAPbI3 grows around the DABr crystal nucleus.There are many DABr crystal nucleus,which leads to small grains,and small crystal grains are more favorable for Ostwald ripening reaction in the heat treatment.By testing the SEM and Fourier infrared transmission spectra of the perovskite film before and after annealing process,we found the reason why different organic ammonium halides affect the grain size of the film that is whether the perovskite film can occur Ostwald rippen process during the heating process.MABr and FABr can induce the increase of film grain size to some extent,while,for PEABr and BABr doped perovskite film,the film grain can not occur Ostwald ripening process due to the absence of Br-,and the particle size does not change.Due to the interaction of DA+ and Br-,the Ostwald ripening can effectively promote the secondary growth of crystal grains,resulting in the large size of the crystalline grains large than1 ?m.