Modification Of The Morphology And Crystal Quality Of CH₃NH₃PbI₃ Films And Its Impact On The Performance Of Perovskite Solar Cells

The rapid emergence of solar cells based on hybrid organic–inorganic perovskite has recently received significant attentionin the photovoltaic community. Within the last five years, the power conversion efficiency（PCE） of perovskite solarcells（PSCs） has increased frommodest value of 3% to a certified value of 21%.This thesisaimed at the key scientific problem in the fabrication of high-efficiency perovskite solar cells, which is interdependent and collaborative features of various part in cells, including preparation ofelectron transport layer（ETL）, andlight absorption layer. It is an importance topic in the research of perovskite photovoltaic that preparation of suitable-morphology and high-crystallization perovskite film.We proposed a method taking ionic liquid as a multifunctional additive to globally modify the preparation process of perovskite film. Furthermore, we followed the variation of the contracture of ETL as well as the morphology and surface hydrophilicity, and clarify the principle of interaction between ETLand thequality of perovskite film.Ionic liquid salt 1-Butyl-3-Methyl Imidazolium Iodide（BMII） was applied as a multifunctional additiveto globally modify the preparation process of perovskite film.Then, mechanism of dynamic control by ionic liquid in the processes of interfacial chemical conversion and grain growth were studied, by monitoring the changes in film morphology, crystallization, photophysical and electrical properties of films.At the same time, we alsosystematically investigated the influence of molecular structure of the intercalated PbI₂ andthestructure ofperovskitewith BMII.As a result, the morphology and crystallinity of the perovskite films could be well controlled. The PCEs of the solar cells were improved from 12% for the reference cell to 15.6% for the additive-enhanced cells, providing a simple and efficient strategy to improve the performance of perovskite solar cells.This project provided a simple and effective method for high-quality perovskite film, and it brought a scientific reference for application of perovskite in solar cells and other optoelectronic devices.Taking nanorod（NR） array as electron transport layer of PSCs not only retains the advantages of three-dimensional heterojunction PSCs, such as the improved mechanical strength and the increased charge separation efficiency, but also overcomes the shortcoming of traditional mesoporous film in charge transport and pore filling. In this work, we prepared TiO₂-NR arrays with different interspace for the deep investigation of the impact of interspace in TiO₂-NR arrays on the PSCs, especially about the pore-filling of perovskite in the channels between TiO₂-NRs, the morphology of perovskite capping layer on the top of TiO₂-NR arrays, as well as the photovoltaic performance of PSCs. Along with the increase of the interspace in TiO₂-NR arrays, the pore filling in the channel between NRs became incomplete, and the thickness as well as the crystal size of perovskite capping layer were reduced gradually. As a result, the highest power conversion efficiency of 10.3% could be achieved through careful optimization of interspace in TiO₂-NR arrays to bring a suitable pore filling and morphology of perovskite layer. Our work about the influence of TiO₂-NR arrays on the properties of pore-filling materials should shed light on the further device engineering of NR-based PSCs and other solid solar cells.ETL plays an important role in planar heterojunction PSCs, by affecting the light-harvesting, electron injection and transportation processes, and especially the crystallization of perovskite absorber. In this work, we utilized a commercial TKD-TiO₂ nanoparticle with a small diameter of 6 nm for the first time to prepare a compact ETL by spin coating. The packing of small-size particles endowed TKD-TiO₂ ETL an appropriate surface-wettability, which is beneficial to the crystallization of perovskite deposited via solution-processed method.The uniform and high-transmittance TKD-Ti O₂ films were successfully incorporated into PSCs as ETLs. Further careful optimization of ETL thickness gave birth to a highest power conversion efficiency of 13.4%, which was much higher than that of PSC using an ETL with the same thickness made by spray pyrolysis. This TKD-TiO₂ provided anuniversal solar material suitable for the further large-scale production of PSCs.The excellent morphologyand the convenient preparation method of TKD-TiO₂ film gave it an extensive application in photovoltaic devices.