Degradation Mechanism And Homojunction Device Of Perovskite Solar Cells

Perovskite solar cells are regarded as a new generation of photovoltaic technology with great application potential due to its high performance.low cost and simple preparation process.With the continuous improvement of photoelectric conversion efficiency,the stability and the device structure innovative design of perovskite solar cells have become an important research focus of their industrialization technology.In order to improve the photoelectric performance and stability of perovskite solar cells.this dissertation explored the degradation mechanism and proposed corresponding optimization methods.Meanwhile,the perovskite homojunction was designed and prepared,which opened up a new direction for the breakthrough of efficient and stable perovskite solar cells technology.Major research paper is as follows:(1)The non-destructive passivation of electron transport layer in perovskite solar cell was realized by using PEIE-2D MOF composite modified material.improving the photoelectric conversion efficiency.Polyethylenimine ethoxylated(PEIE)and tellurophene-based two-dimensional metal organic framework(2D-MOF)composites can form uniform and smooth surface passivating layer on the TiO2 electron transport layer.PEIE-2D MOF can passivates Ti3+-Vo defects in TiO2 through electron injection effect,reducing the interfacial recombination of photocarriers.And the photocatalytic activity of TiO2 was reduced.enhanceing the stability of the solar cells.At the same time,the smooth substrate interface brought by PEIE-2D MOF can effectively improve the crystal quality of the perovskite film.enhancing the electron extraction and carrier directional transmission,which improved photoelectric conversion efficiency of the solar cells.After optimized by PEIE-2D MOF composite modification layer,the photoelectric efficiency of perovskite solar cells is improved to 22.22%.Using PEIE2D MOF composite material to modify the TiO2 electron transport layer is a novel interface nondestructive passivation technology,which provides a new idea for industrial development of perovskite solar cells.(2)The key role of Ti3+ defects in TiO2 during UV degradation of perovskite solar cells was investigated,and the two-stage UV degradation phenomenon was revealed.PEIE was used to block the transformation of Ti3+ defect and enhance the UV stability.The degradation process of perovskite solar cells under UV irradiation consists of two stages.In the first slow recombination degradation stage,the Ti3+ defects corresponding to the oxygen vacancy in TiO2(Ti3+-Vo)will be converted into active Ti4+-Vo combination center under UV excitation,resulting in the photocarrier loss.Furthermore,Ti4+-Vo states can convert back into Ti3+-Vo states through oxidizing I-,which result in the accumulation of I3-.The accumulation of I3-ions can accelerate the decomposition of perovskite materials,initializing the fast decomposition degradation stage.Based on the degradation mechanism mentioned above,we propose a UV stability improvement method by PEIE to modify the TiO2 layer inhibiting the conversion of Ti3+-Vo to Ti4+-Vo.The optimized perovskite solar cells remain 75%of the initial efficiency(20.51%)after 72 days of UV aging,while the control group failed completely.(3)Based on the self-doping characteristics of perovskite films,a perovskite homojunction model was established,and a perovskite homojunction solar cell was prepared by gas-liquid combined deposition process.n-doped perovskite films were prepared by controlling the precursor concentration and annealing temperature.Then.p-type perovskite was deposited on n-type layer by vapor evaporation,and the perovskite homojunction with rectification property was constructed.The opposite diffusion of majority carriers on both sides of the perovskite homojunction establishes a built-in electric field whose strength is determined by the doping concentration of the perovskite material.Perovskite homojunction has photovoltaic effect,which can drive the separation and directional transmission of photocarriers,realizing the photoelectric conversion process.The photoelectric conversion efficiency of perovskite homojunction solar cells prepared by gas-liquid combined deposition method is over 8%.The perovskite homojunction solar cells abandon the traditional electron/hole transport layer,which is beneficial to simplify the cell structure and improve the stability.(4)The mechanism of built-in electric field degradation caused by doping defect migration in perovskite homojunctions was investigated.Phenethylammonium iodide(PEAI)was used to suppress defect migration and improve the working stability of perovskite homojunction stability.The diffusion compensation of doping defects can reduce the perovskite doping concentration and the photoelectric performance of the solar cells.Then.PEAI was introduced into perovskite film to inhibit the diffusion of doping defects through vacancy filling and ion bonding.The photoelectric conversion efficiency of the perovskite homojunction solar cells optimized by PEAI is increased from 8.6%to 9.6%.and it could still keep more than 80%of the initial efficiency after 1000 hours of aging.The inhibition of doping defect diffusion by PEAI is of great significance for improving the efficiency and stability of perovskite homojunction solar cells.