Research On Interface Modification Of Lightabsorbing Layer And Photovoltaic Performance

In recent years,perovskite solar cells using organic-inorganic hybrid perovskite materials as the light-absorbing layer have received extensive attention and research due to their high efficiency,low cost,and solution method preparation.Perovskite solar cells consist of electron transport layer,perovskite layer,hole transport layer and electrodes.The interfaces widely exist in the perovskite solar cell and have a huge impact on the carrier transport and recombination,which in turn have an important impact on the photovoltaic performance and stability of perovskite solar cells.Based on this,the research on interface modification is of great significance for the construction of efficient and stable perovskite solar cells.This thesis has conducted a detailed study on the interface modification of perovskite solar cells.The main research content includes the modification of the perovskite layer/hole transport layer interface,the perovskite layer/electron transport layer interface and the internal interface of the perovskite layer.Specific research content is as follows:（1）A small molecule ammonium salt called PTABr is used to modify the interface of perovskite layer/hole transport layer.Studies have shown that the introduction of PTABr molecules is beneficial to improve the hydrophobicity of the perovskite film.On the one hand,the increasement in hydrophobicity comes from the hydrophobic alkyl chain group of PTABr molecules.Without changing the crystal structure,surface morphology and absorbance of the perovskite,the perovskite film modified by PTABr has lower trap density and longer carrier lifetime.The PTABr-modified perovskite solar cells have achieved a photoelectric conversion efficiency of 20.12% and have good long-term stability and repeatability.Based on the calculation of DFT theory,it can be concluded that PTABr is self-assembled on the surface of perovskite film with the alkyl chain facing upward,and the functional group can passivate the PbI₃^- defect in the perovskite,causing the shift of the Pb atom relative to the equilibrium position,making it more difficult to combine with water molecules,hence enhancing the stability of perovskite in air atmosphere.（2）A small ester molecule PDCA is used to modify the interface of perovskite layer/electron transport layer.The wettability of this interface is changed by introducing interface modified molecules,thereby gaining high-quality perovskite films.Studies have shown that the surface hydrophobicity of PDCA-modified titanium dioxide has been improved,resulting in fewer perovskite nucleation centers exist on the surface,which is conducive to the formation of large and flat perovskite films with larger grain sizes.At the same time,the introduction of the molecule is beneficial to enhance the carrier transport in the interface,and the perovskite films have a lower defect density,which is beneficial to reduce the carrier loss caused by the recombination at the interface.The PDCA-modified perovskite solar cells have obtained a photoelectric conversion efficiency of 20.21% and have excellent steady-state output performance.（3）Common organic P-type dopant TTF-4 and N-type dopant F4-TCNQ are used to dope the perovskite precursors,and the pressure-assisted method is used to prepare the homogeneous perovskite films.This method is beneficial to improve the internal interface of the perovskite films.Studies have shown that there is a top-to-down transfer of the perovskite components during the preparation process,and the perovskite films prepared by this method have the characteristics of large grain size and flatness.The work function of perovskite film is reduced by this method.Combined with steady-state PL,transient PL and electrochemical impedance spectroscopy,a conclusion can be drawn that the perovskite film prepared by the PAHJ method is more conducive to carrier transport and reduce the trap density of perovskite film.The photoelectric conversion efficiency of the perovskite solar cells prepared by the PAHJ method reach 20.28% and show fast response speed and good stability in the steady-state output test.