The Preparation And Performance Optimization Ofperovskite Solar Cell Based On TiO₂ Nano-film

With the emergency of energy crisis,the use of solar energy has been developing rapidly.In the process of using solar energy,solar cell is considered to be one of the most effective methods.In recent years,the new type of perovskite solar cells?PSCs?becomes a hotspot in the research of photovoltaic field,due to its low-cost and high power conversion efficiency characteristics.In the classical structure of PSC,mesoporous oxide nanoparticle is generally used as support layer to transport electron and support pervoskite layer.Nano-TiO₂ film has been widely used as support layer in PSC for its large specific surface area and excellent electronic transmission performance.The research of this thesis was discussed around the PSC with TiO₂ mesoporous structure.First of all,the influence of TiO₂ mesoporous layer thickness on meso-PSC has been researched.A series of TiO₂ mesoporous layer with different thickness?150 nm,250 nm,400 nm and 600 nm?were prepared.Using methylamine lead iodine?MAPb I₃,MA=CH₃NH₃?as light soaking layer,the substrates with different thickness were assembled into PSC and tested.Scanning electron microscopy?SEM?and ultraviolet-visible spectrophotometer?UV-Vis?were used to characterize the microstructure and optical absorption ability of the meso-TiO₂&MAPbI₃ films.The results show that when TiO₂ layer thickness changes from 150 nm to 400 nm,thicker TiO₂ mesoporous layer facilitates the infiltration of MAPbI₃,and the light absorption ability of PSC was also increased with the increasing of TiO₂ layer thickness.However,the electrochemical impedance spectroscopy results,which was used to analysis the interface dynamic process of PSC,indicate that when TiO₂ mesoporous layer thickness further increases to 600 nm,the electron transport resistance of PSC device was increased.In the end,the PSC based on 400-nm-thick TiO₂ mesoporous layer achieved higher photoelectric conversion efficiency of 13.56%.Secondly,according to the poor stability of MAPbI₃ material,halogen substitution?Br?I?were used to improve the stability of MAPbI₃ material and the assembled devices.Moreover,the two-step solution process was adopted,which is simply and easily to control and the Pb(I_1-xBr_x)₂?0?x?0.4?was used as seed layer to prepare MAPbI_3-2xBr_2x material.The MAPb I_3-2xBr_2x-based PSCs with TiO₂ mesoporous structure were assembled and tested.It is found that when x value changes from 0.2 to 0.4,the Pb(I_1-xBr_x)₂ films become denser which could hinder the infiltration of iodine meyhylamine?MAI?during the subsequent preparation.As a result,plenty of residual PbI₂ are founded in the corresponding MAPbI_3-2xBr_2x films by X-ray diffractometer?XRD?.The existence of PbI₂ not only reduced the purity of MAPb I_3-2xBr_2x film but also hindered electron transporting to FTO electrode.However,when x value changes from 0 to 0.1,less PbI₂ residue was founded in MAPbI_3-2xBr_2x films,and the efficiency of corresponding PSC could reach 12%.The results of device stability show that after exposed to the air two weeks later,the PSC using MAPbI_2.8Br_0.2 as light soaking layer remain 80%of its initial efficiency,while the PSC using MAPbI₃ as light soaking layer only remain 50%of its initial efficiency.Therefore,through halogen substitution and two-step preparation,superior performance and excellent stability were achieved in the PSC based on MAPb I_2.8Br_0.2 film.During the process of two-step method,the residual of Pb I₂ caused by denser Pb(I_1-xBr_x)₂film greatly influence the performance of PSC.In order to improve this phenomenon,three kinds of alcohol solution?isopropanol,methanol and ethanol?were introduced to treat Pb I₂seed layer.At the same time,the purity of MAPb I₃ film and photovoltaic performance depending on Pb I₂ morphology has been studied.The results of microscopic characterization show that all of three different alcohols can improve the morphology of PbI₂ film,and the Pb I₂ films treated with ethanol exhibited the most porous structure.Porous PbI₂ film could facilitate the diffusion of MAI in the second step and high purity of MAPb I₃ membrane has been produced as a result.Photoeletric conversion efficiency tests indicate that the PSC performance treated with ethanol has been enhanced about 30%than that before processing.Finally,combining halogen regulation and ethanol treatment process,the PSC device using MAPb I_2.6Br_0.4 as light soaking layer exhibited excellent performance with high efficiency of15.53%and long term stability.