Preparation Of Efficient,Stable,and Lead-free Perovskite Solar Cell And Chlorine Doping Investigation

In recent years,organic-inorganic hybrid perovskite solar cells have attracted extensive attention in the photovoltaic community due to their high efficiency,low cost and simple process.However,MAPbI₃perovskite solar cells have many problems,such as fabrication methods,material stability,and toxicity of Pb.It is urgent to explore new preparation methods and material systems to obtain high-efficiency,air-stable and lead-free perovskite photovoltaic devices.Research shows that the key element Cl can effectively improve the carrier diffusion length and film quality,reduce the carrier recombination,and then improve the photovoltaic performance of devices.To this end,we firstly employed a simple gas-assisted solution deposition process(LP-VASP)with high controllability and film quality to grow MAPbI₃ perovskite films,and then doping with Cl to obtain high-efficiency MAPbI_3-xCl_xorganic-inorganic hybrid perovskite solar cells.At the same time,due to the poor thermal stability of MAPbI₃,we synthesized the inorganic CsPbBr₃quantum dots by hot-injection method for fabricating air-stable all-inorganic perovskite solar cells.Finally,to solve the toxicity of Pb,we used spraying method to prepare lead-free Cs₂Sn I₆solar cells.The content of this thesis is as follows:Firstly,the gas-phase growth and photovoltaic properties of Cl-doped MAPbI₃films are first studied.PbI_2-xCl_xfilms are obtained by adding Cl elements into the precursor solution,and then MAPbI_3-xCl_xfilms are obtained by gas-solid reaction with MAI vapor.The effect of Cl on MAPbI₃thin films is studied by accurately controlling the reaction time of chemical vapor deposition(CVD).It is found that MAPbI_3-xCl_xis only an intermediate and Cl disappears with the increase of CVD reaction time,and thus there has no effect on the optical band gap of the films.However,the introduction of Cl can effectively improve the morphology of the films and increase their grain sizes,which plays an auxiliary role in the nucleation and crystallization of the films.At the same time,Cl doping can effectively reduce the resistance of the films,increase the carrier mobility,and improve the cell performance significantly.The perovskite solar cell with a high efficiency of 17.82%has been successfully fabricated in this work,reaching a high-level of CVD-processed perovskite solar cells.Secondly,the preparation and photovoltaic properties of CsPbBr₃inorganic perovskite quantum-dot films are studied.The inorganic CsPbBr₃quantum dots with good thermal stability are synthesized by hot-injection method,and then for fabricating air-stable all-inorganic perovskite solar cell,the uniform and compact CsPbBr₃films are obtained by multiple spin-coating and annealing methods.This new method overcomes the solubility problem of bromide.And we can adjust the film thickness by changing the coating times.An effective all-inorganic perovskite solar cells with an efficiency of4.3%is obtained,and it was found that a small amount of Cl doping can greatly improve the stability of the inorganic CsPbBr₃cells.Thirdly,the preparation and photovoltaic properties of lead-free Cs₂Sn I₆thin films are studied.To solve the toxicity issue of Pb,we use Sn to replace it.As such,a low-cost simple solution synthesis method is developed for synthesizing air-stable tetravalent Cs₂Sn I₆powder,and then high-quality Cs₂Sn I₆films are prepared by a spraying process,which can effectively overcome many problems,such as expensive vacuum process and difficulty of spin-coating films.It is found that the Cs₂Sn I₆films have good moisture and oxygen resistant abilities,and show excellent thermal stability,which starts to decompose above 300?.Finally,environmental friendly lead-free Cs₂Sn I₆solar cells are also achieved.Research shows that a small amount of Cl doping can increase the current and improve the performance of the solar cells.