The Study Of Surface Modification Of Two-dimensional MXene And Its Application For Interface Engineering In The Perovskite Solar Cells

As the third-generation solar cells,the perovskite solar cells(PSCs)have been widely concerned in the past ten years because of its excellent photoelectric properties.Owing to continuous optimizations in terms of composition control,interface engineering and device structure design,their power conversion efficiencys(PCE)have increased from 3.9 % to 25.5 % up to now.In the device structure of perovskite solar cells,the electron and hole transport layer play an important role in the charge extraction and device performance of perovskite solar cells.Ti O2 and Sn O2 are the most commonly used electron transport materials for high-performance perovskite solar cells.However,Ti O2 usually needs high-temperature sintering process for efficient electron extraction ability in perovskite solar cells,which hinders its application for large-scale commercialization.By contrast,Sn O2 can be prepared at low temperature.However,large amounts of the defects are usually generated in the bulk Sn O2 or Sn O2/perovskite interface during the formation process,which would lead to deterioration of the device performance.Therefore,the exploration of efficient novel electron transport materials is still one of the key issues in perovskite research.The new two-dimensional MXene material has excellent properties like graphene,such as high conductivity,flexibility and hydrophilicity.These properties give MXene the potential to be an effective electron transport material with tunable functional groups,which enable surface modification and defect passivation in PSCs.Thus,this thesis takes Ti3C2 Tx which is a typical material in MXene,as the research subject.By regulating the surface functional groups and properties of Ti3C2 Tx MXene,we studied its application for new-type electron transport layer and interface engineering in perovskite solar cells.The specific research contents are shown as follows:1.Three methods were used to produce high quality perovskite films,including the vapor deposition,the vapor-assisted solution process and the solution deposition,and were thoroughly investigated in terms of their influence on film formation process and device performances.As a result,efficient perovskite solar cells with PCE exceeding 20 % were obtained by the solution deposition method.2.An exploratory study of Ti3C2 Tx as a new electron transport layer material in PSCs was carried out.The Ti3C2 Tx electron transport layer is prepared by low temperature solution process,followed by surface oxidation.The surface oxidation could not only control the elementary composition and chemical bonds of Ti3C2 Tx to optimize the surface energy and wettability,but also effectively tune the work function of Ti3C2 Tx,leading to reduced trap density and improved charge extraction at the Ti3C2Tx/perovskite interface.Finally,the perovskite solar cell achieves the PCE of 20.42 %,as well as the stability is enhanced in ambient atmosphere.3.The influence of different halogen surface functional groups(Br,I and Cl)on the surface properties of MXene and its application for interface engineering in perovskite solar cells were studied.We prepared the Ti3C2X2 films with different halogen functional groups by low temperature solution method and explored the impacts on perovskite film morphology and device performance.This study further demonstrated the tunability of MXene surface functional groups and its great potential in interface engineering for high-performance perovskite solar cells.