Fumigation-assisted Two-step Vapor Deposition Of Perovskite Films And Solar Cells

After more than ten years of development,the efficiency of perovskite solar cells(PSC)has increased from the initial 3.9%to more than 25%.However,most of the high-efficiency devices are prepared by solution spin coating,and it cannot prepare devices on complex curved substrates.In contrast,the vapor deposition method is basically not limited by the substrate,and is mainly divided into the one-step vapor deposition method and the two-step vapor deposition method.The biggest obstacle of the two-step vapor deposition method is that methylammonium iodide(MAI)is not easy to diffuse in PbI₂.Problems to be solved in this thesis include non-spin-coating preparation of the hole transport layer(HTL)and promotion of the diffusion of MAI in dense PbI₂.Details are as following:The HTL used as the window layer in the invert PSC is usually prepared by the solution spin coating method that cannot form a whole film on a curved substrate.In this thesis,HTLs were prepared by vapor deposition and dip-coating methods.Among them,MeO-2PACz can match the energy level of MAPbI₃,and compared with other HTLs,the open-circuit voltage(V_OC)of the device was increased from less than 1.0 V to 1.06 V.Finally,we used the dip-coating method to prepare MeO-2PACz as the HTLs of invert devices,which achieved a V_OC of more than 1.0 V and a photoelectric conversion efficiency of more than 18%.In order to promote the diffusion of MAI in PbI₂,in this thesis we have adopted methods including illumination assistance,optimization of PbI₂ evaporation and MAI spraying conditions,and the use of solvents to treat the surface of PbI₂.The results show that compared with pristine PbI₂,perovskite prepared by the reaction of PbI₂that is pretreated with 1,3-dimethyl-2-imidazolidinone(DMI)has nearly no residual PbI₂,and the crystallinity of perovskite is better.Finally,we achieved a photoelectric conversion efficiency of 19%,and the device stability was improved.After 28 days of white light irradiation,the device maintained 93%of the initial efficiency.Later,the mechanism of the fumigation-assisted vapor deposition method was studied in this thesis.We find that DMI can promote the diffusion of MAI,so that grains in the as-prepared perovskite film are vertically monolithic and the film has no interface voids.Grazing-incidence wide-angle X-ray scattering(GIWAXS)analysis shows that the perovskite prepared by the fumigation-assisted two-step vapor deposition method contains less PbI₂and shows no obvious crystallization orientation,which is conducive to the free transport of carriers.Transient fluorescence confocal microscopy and deep-level trap spectroscopy(DLTS)tests show that the perovskite film prepared by this method has a longer fluorescence lifetime and fewer defects,so that the device shows high efficiency and good stability.Finally,in order to verify whether the method can be used for surface conformal preparation,we successfully prepared a perovskite film conformal to the original surface of a copper indium gallium selenide(CIGS)device and with vertical monolithic grains.At last,we fabricated a perovskite device on a curved substrate with a curvature radius of 2.5 cm,with an efficiency of 8.93%.This thesis provides a feasible manufacturing method for the preparation of tandem devices and curved perovskite devices.