Perovskite CH₃NH₃PbI₃ Thin Films And Solar Cells Prepared By Single Source Physical Vapor Deposition Method

In order to form a uniform, smooth, continuous perovskite film for high performance pervoskite, one step spin coating method, two step sequential method and dual source vapor deposition were comparative studied. Then a single source physical vapor deposition method was demonstrated for the fabrication of the perovskite CH₃NH₃PbI₃ thin film. At last, high quality perovskite solar cells based on the structure of ITO/PEDOT:PSS/CH₃NH₃PbI₃/PC61BM/Ag were prepared by ingle source physical vapor deposition method.Firstly, One-step spin coating method was employed to directly deposit the perovskite materials from a mixture precursor solution of PbI₂ and CH₃NH₃ I in a polar solvent, such as r-butyrolactone?GBL?, followed by annealing at 100?C to remove the additives and crystallize perovskite thin films. However, it is difficult to find a suitable solvent that can dissolve both components and generally hard to control the reaction rate between CH₃NH₃ I and PbI₂. The perovskite CH₃NH₃PbI₃ thin films with pinholes were unexpected.Secondly, to create a uniform perovskite film, a modified two-step sequential deposition method has been developed. A uniform, homogeneous, and small size PbI₂ nanocrystal is deposited via vapor evaporation, firstly, and then a hot CH₃NH₃ I solution is spin coating onto the prepared PbI₂ thin film to form perovskite thin films in a short time. The results demonstrate that homogeneous, compact, complete surface coverage, good crystallinity and pinhole-free CH₃NH₃PbI₃ thin films, which will be suitable for perovskite solar cells applications., are fabricated by a modified sequential deposition.Thirdly, the CH₃NH₃PbI₃ thin film prepared by modified dual-source vapor evaporation was proposed. An ultra-thin PbI₂ layer was deposited firstly, and then CH₃NH₃ I and PbI₂ were evaporated simultaneously to form CH₃NH₃PbI₃ thin film. The results show that flat, uniform,smooth, less porous and good crystallinity perovskite thin films without impure phase are formed by the modified dual-source vapor evaporation. The ratios of Pb/I accord with the nominal MAPb I3 stoichiometry and the band gaps are about 1.60 e V close to the theoreticalvalue of 1.55 e V. The properties of CH₃NH₃PbI₃ thin film fabricated by this method are suitable for perovskite solar cells applications.What is more, we demonstrate a facile and efficient method for the fabrication of the perovskite thin film. With a single source physical vapor deposition?SSPVD? method, the CH₃NH₃PbI₃ powder is converted to the gas phase of CH₃NH₃PbI₃ by evaporation. Then the gas phase transported and deposited back on the surface of the sample. This is different from the methods, such as one-step spin coating method, two-step sequential method, vapor assisted solution process, and dual-source vapor evaporation, have been used to prepared MAPb I3 thin films with reacting between the organic and inorganic sources. What is more, the conventional methods require an invariable subsequent thermal annealing treatment to remove the additives and/or crystallize perovskite thin films. However, an inappropriate annealing time?excessive or inadequate? or temperature?over high or low? would result in poor film morphology with pinholes or undesirable crystallization due to the difficulty to control the evaporation of solvents or crystallize perovskite thin film. In contrast, with this method, gases of CH₃NH₃PbI₃ are guided to the sample, which does not undergo a chemical reaction on the way to the sample or on the surface of the sample. Along with advantages of the single source physical vapor deposition progress without reaction, the problems,such as, high reaction rate between CH₃NH₃ I and PbI₂, lack of suitable solvent for CH₃NH₃ I and PbI₂, dissolution of the perovskite film, simultaneous control of evaporation rates of the organic and inorganic sources, impurity of PbI₂, improper heat treatment and so on, are effectively avoided and a uniform, smooth, nonporous and complete surface coverage perovskite thin films with high level of phase purity and good crystallization are formed.Finally, the initial results of device with values of 19.47 m A/cm2, 0.932 V and 60% for Jsc, Voc and the fill factor, respectively, yielding a PCE of 10.90% based on SSPVD were obtained, suggesting its promising application for significant optimization in pervoskite CH₃NH₃PbI₃ solar cell efficient.