| Methylamine-lead-iodide(MAPbI3)perovskite material is an excellent solar cell material with high light absorption coefficient and carrier mobility.However,a large number of defects exist at both the upper and buried interfaces of MAPbI3 thin films,leading to severe non-radiative recombination of carriers,which significantly reduces the photoelectric conversion efficiency and operating lifetime of solar cells,and is one of the important scientific problems hindering their application and development.To this end,this thesis focuses on the interface passivation process of MAPbI3 thin film and transport layer,explores the intrinsic mechanism of interface passivation,and develops passivation processes such as buried interface and surface interface to improve the photoelectric conversion efficiency and stability of solar cells.First,in this thesis,a potassium hydroxide(KOH)passivation process was developed to modify the interface between the perovskite layer and the electron transport layer in response to the problem of defects at the buried bottom interface of MAPbI3 perovskite thin films.It was found that KOH was able to form coordination interactions with titanium ions and oxygen ions on the surface of the electron transport layer(TiO2).On the other hand,the strong interaction between potassium ions and bromine ions induced the distribution of bromine ions in the perovskite film near the buried interface,which promoted the close connection between the electron transport layer and the perovskite layer.The introduction of KOH enhanced the quality of the perovskite film,reduced the non-radiative recombination at the interface between the perovskite layer and the electron transport layer,and enhanced the carrier extraction and transport.The photoelectric conversion efficiency of the solar cell was increased from 15.33%to 17.11%after the treatment of the buried bottom interface by KOH,and the stability was significantly improved.Secondly,a method of in situ construction of vertically oriented twodimensional perovskite to achieve passivation of defects on the surface of perovskite thin films was developed in this thesis to address the problem of residual lead iodide at the surface interface of MAPbI3 perovskite thin films.The vertically oriented(PEA)2PbI4 modified perovskite surface interface was prepared by introducing methylammonium chloride(MACl)into the post-treatment solution of phenethylammonium iodide(PEAI)to regulate the growth orientation of the twodimensional perovskite using residual PbI2 on the surface of MAPbI3 perovskite thin films.MACl has a strong coordination ability,easily volatile,and does not introduce impurities.It was found that the two-dimensional perovskite posttreatment could reduce the defects caused by the large amount of residual lead iodide on the surface of the film,and the two-dimensional perovskite was mainly distributed at the grain boundaries of the perovskite grains,without changing the surface morphology of the perovskite crystals.The introduction of MACl can induce the two-dimensional perovskite phase to form a vertical growth orientation and improve the carrier transport capability.Therefore,the vertical growth orientation of two-dimensional perovskite modified surface can effectively reduce the non-radiative recombination on the surface of the film,promote the photogenerated carrier migration,and reduce the charge accumulation at the interface.The two-dimensional perovskite passivation process designed in this thesis increased the photoelectric conversion efficiency of solar cells from 17.71%to 18.65%,and the device stability was also significantly improved.Then this thesis developed an acetate ionic liquid passivation process for the surface defects of perovskite films with uncoordinated lead ions on the surface of MAPbI3 films.The ionic liquid 1-ethyl-3-methylimidazole acetate([EMIM]Ac)was used to post-treat the perovskite surface and passivate the uncoordinated lead sites at the surface interface of the film.It was found that[EMIM]Ac does not enter the perovskite lattice and present on the surface of the perovskite film,thus not changing the crystalline quality and band gap of the perovskite.The carbonyl group in acetate can form an interaction with lead ions and inhibit the formation of metallic lead on the surface,effectively reducing the defects associated with lead ions.The post-treatment of[EMIM]Ac on perovskite films can reduce the nonradiative complex on the surface of perovskite films,reduce the density of defect states of the films,facilitate the transport of photogenerated carriers,improve the quality of the films,and reduce the loss of open-circuit voltage.The photoelectric conversion efficiency of solar cells treated with[EMIM]Ac was increased from 16.95%to 19.02%.In order to further passivate the surface defects of MAPbI3 perovskite films and enhance the photoelectric conversion efficiency of solar cells,the passivation of MAPbI3 perovskite films with different alkyl chain lengths of imidazolium-based ionic liquids was investigated in this paper.The passivation of the surface of the perovskite thin films was carried out using acetate ionic liquids with different alkyl chain lengths(alkyl chain containing 2,4,6 and 8 carbons,respectively).It was found that the surface treatment with different alkyl ionic liquids did not affect the crystal structure and light absorption of perovskite.The ionic liquids are mainly present on the surface of the perovskite films,acting as a bridge between the perovskite layer and the hole transport layer.With the growth of the alkyl chain length,the photoelectric conversion efficiency of the cell exhibited a trend of increasing and then decreasing.Although ionic liquid passivation would enhance the solar cell efficiency,the alkyl chain length would affect the extraction and transport of interfacial charge carriers,and long alkyl carbon chains would hinder the interfacial charge transfer.The study showed that the highest photoelectric conversion efficiency of solar cells was achieved at 19.57%when the number of carbon atoms in the imidazole alkyl chain was 4. |
PDF Full Text Request