Study On Amino Acids As Additives To Improve The Photoelectric Properties Of Perovskite Solar Cells

As renewable energy sources are consumed continuously,the solar cell technology is gradually attracting attentions.Perovskite solar cells（PSCs）have been extensively studied because of their band gap tunability,high carrier transport efficiency and high absorption coefficient.Since 2009 when a solid-state organic-inorganic halide perovskite material was used as the light-absorbing material for PSCs to achieve a power conversion efficiency（PCE）of 3.8%,the highest certified efficiency has reached25.7%after more than a decade of development.The devices of PSCs have some shortcomings such as poor interfacial contact between the absorbing layer and the transport layer resulting in blocked charge transfer,low charge transfer capability in the transport layer,and a large number of grain boundaries in the absorbing layer resulting in non-radiative recombination.Therefore,reducing the defects in PSCs is one of the important ways to improve their PCE.Improving the quality of perovskite films can effectively reduce the defects and improve the PCE.Therefore,a series of studies have been conducted in this thesis to improve the quality of perovskite films while increasing the PCE of PSCs.A review of the literature shows that N atoms in amino groups passivate perovskite defects by forming hydrogen bonds with halogen atoms,while carboxyl groups can be coordinated with undercoordinated Pb atoms to passivate perovskite defects.In this thesis,natural amino acids are selected as additives to improve the quality of perovskite films and to investigate the defect passivation effect and mechanism.The main work in this thesis is as follows:（1）The effect of DL-histidine（DL-His）additive on the photoelectric properties of perovskite solar cells.The results of XRD and SEM proved that DL-His doping promoted the reaction between Pb I₂ and organic salts.The optical properties of the perovskite film were characterized by UV,PL and TRPL,which proved that the non-radiative recombination in the perovskite film was reduced after DL-His doping.The results of EIS,LSV,M-S and EQE_EL confirmed that the doping of DL-His reduced the non-radiative recombination inside the PSCs and improved the carrier mobility.XPS characterization proved that DL-His coordinated with Pb and I atoms in perovskite,respectively,thus realizing defect passivation.The efficiency of PSCs increased from20.01%to 22.25%after DL-His doping,and the stability of perovskite films and PSCs was also greatly improved.（2）The modified device exhibits a greatly enhanced power conversion efficiency of 22.7%,which is unprecedented for PSCs doped with natural amino acids,and 3000 h stability in ambient air is achieved.Through systematical characterizations,it is concluded that D-Asp could result in thicker film formation,outstanding perovskite film morphology,and reduced defect sites passivated by the multiple functional groups.The results prove that the performance and stability of the state-of-the-art mixed ion PSCs with regular architecture could be effectively enhanced by D-Asp.The minimum usage of the natural product as an additive is beneficial for the fabrication process and cost-control in the industrialization of PSCs.This work also highlights the different passivating mechanisms for the molecules with multiple functional groups which are meaningful for materials design.