Study On The Carbazole-based Quasi Two-dimensional Perovskite Solar Cells

As a kind of new concept solar cell,the perovskite solar cell is a solar cell that uses perovskite crystal organic-inorganic halide semiconductor material as the light absorbing material.It has the huge advantage of high photoelectric conversion efficiency and low manufacturing cost.However,the inherent instability of traditional three-dimensional organic-inorganic halide perovskites has become one of the key factors hindering the commercialization of perovskite solar cells.To overcome this challenge,people tried to replace the three-dimensional perovskite material with a quasi-two-dimensional perovskite material with a hydrophobic layer.In addition to good environmental stability,the quasi-two-dimensional perovskite material also has a unique quantum well structure inside.In a general sense,the quantum well structure can enhance the binding energy of excitons,which is not conducive to improving the exciton separation of perovskite solar cells and reducing the photoelectric conversion efficiency.In addition,the relationship between the structure and properties of quasi-two-dimensional perovskite materials also needs urgent research.How to use this emerging material with stability advantages in perovskite solar cells and obtain high photoelectric conversion efficiency is of great significance.The main contents of this thesis include the following three parts.First,obtain a high-quality carbazole-based quasi two-dimensional perovskite thin film material.We used scanning electron microscopy to characterize the carbazole reference two-dimensional film spin-coated with different n-value precursor solutions,and found that the material can form a dense and flat film,which is the premise of making thin-film photovoltaic devices.Then using X-ray diffraction,ultraviolet absorption and steady-state fluorescence to carry out a series of characterization of the carbazole reference two-dimensional perovskite film,to verify the existence of the carbazole-based quasi two-dimensional perovskite material.And the spectrum gradually red-shifted with the decrease of the proportion of carbazole large cations,in line with the theory.In terms of stability,we compared the n=5 carbazole-based two-dimensional perovskite film with the phenethylamine-based quasi two-dimensional perovskite film.The carbazole-based two-dimensional quasi perovskite film exhibited an amazing stability far superior to that ofphenethylamine-based quasi two-dimensional perovskite film when immersed in water,reflecting the research value of the material.Secondly,the vertical orientation of the carbazole-based two-dimensional quasi perovskite layer on the substrate is optimized.The original carbazole-based two-dimensional quasi perovskite solar cell has a low photoelectric conversion efficiency.We get quasi-two-dimensional perovskite crystallized perpendicular to the substrate by doping ammonium thiocyanate(NH₄SCN)into the precursor solution.First,the X-ray diffraction patterns of films with different concentrations of NH₄SCN were used to determine the doping concentration to obtain the best crystallization of the films.From the grazing incidence wide-angle X-ray scattering(GIWAXS),it can also be seen that the film containing additives exhibits high crystallinity perpendicular to the growth of the substrate.Then the electrical and photovoltaic characterizations of the thin film devices before and after optimization are carried out.The experimental results show that the optimized thin films have better carrier transmission performance,and the best photovoltaic devices achieve a conversion efficiency of 8.36%.Finally,based on the vertical orientation,the multi-quantum well structure of the carbazole-based two-dimensional quasi perovskite is adjusted to overcome the effect of strong exciton binding energy on battery efficiency.During the preliminary investigation of the ccarbazole-based two-dimensional quasi perovskite,it was found that the ultraviolet-visible absorption spectrum for n greater than 1 shows that the film contains a plurality of n-valued phases after crystallization is completed.We found that the distribution of n in the film can be adjusted by chlorobenzene antisolvent.The ultrafast time-resolved transient absorption spectroscopy(TA)was used to characterize the films,and it was found that the film with anti-solvent crystallized form the distribution of low n phase at the top and high n phase at the bottom.The untreated film is reversed.Due to the adaptation of the energy level,the film without anti-solvent is suitable for p-i-n devices,and the device with anti-solvent film is suitable for n-i-p devices.The highest photoelectric conversion efficiency obtained from the n-i-p device with anti-solvent,and the efficiency is 10.49%.Based on the chlorobenzene antisolvent-treated solar cell,the unencapsulated device still has about 80%of the initial photoelectric conversion efficiency after being stored in the air for 1000 hours.