Design And Structure-Property Relationship Studies Of Additives In Printable Mesoscopic Perovskite Solar Cells

Solar power generation technology is one of the key strategies to address the increasingly serious energy shortage and greenhouse effect,and it is of great significance to promote the transformation of energy structure and achieve net zero CO₂ emissions as soon as possible.As an emerging solar cell technology,perovskite solar cells（PSCs）have developed rapidly,and the highest power conversion efficiency（PCE）has reached 25.8%.Printable mesoscopic perovskite solar cells（p-MPSCs）have the advantages of low material cost,simple fabrication process and easy scale-up,showing broad industrial prospects.Due to the unique device structure,perovskite materials crystallize in the thick film scaffold of more than ten microns,which is composed of mesopores and pores.The corresponding crystallization process is more complex than that of conventional PSCs,and the crystallization regulation is more difficult.In addition,the growth of perovskite grains is confined by mesopores,resulting in fine grains with numerous grain boundaries.Therefore,it is necessary to develop crystallization regulation and defect passivation methods suitable for p-MPSCs.Based on the additive strategy,this dissertation focuses on the crystallization kinetics,crystallization regulation and defect passivation of perovskites under mesopore-confined conditions.The main contents include:（1）A series of amino acids with different alkyl chain lengths were introduced into methylammonium lead iodide/γ-butyrolactone（MAPbI₃/GBL）system as bifunctional additives,respectively.The effects of amino acids with different chain lengths on the crystal structure,film morphology and photoelectric properties of perovskites were studied,and the differences in photovoltaic performance of the corresponding devices were further compared and analyzed.The in-situ grazing incidence wide-angle X-ray scattering（GIWAXS）characterization technique was used to investigate the real-time crystallization process of MAPbI₃ perovskite in mesopores after the introduction of amino acids with different chain lengths.It is shown that the amino acid with moderate chain length can induce the formation of the ordered precursor phase and intermediate phase to avoid the direct transformation from precursor sol phase to perovskite phase,thus delaying the crystallization of perovskite and facilitating the uniform nucleation and growth of MAPbI₃ in mesopores.（2）The mechanism of how amino acids with different spatial configurations affect the crystallization of MAPbI₃ perovskite was studied.Cis-4-aminocyclohexanecarboxylic acid and trans-4-aminocyclohexanecarboxylic acid with identical functional groups but different spatial configurations were respectively introduced into MAPbI₃/GBL system,but only t ACA can improve the crystallization and infiltration of MAPbI₃ in mesopores and increase the PCE of p-MPSCs from 6.39%to 13.30%.It is demonstrated that the spatial configurations of amino acids affect their roles in the crystallization of MAPbI₃ by influencing the formation of hydrogen bonds and coordination bonds.The t ACA molecules form hydrogen bonds between carboxyl groups,and their amino groups can anchor to the[PbI₆]octahedron of the perovskite through hydrogen bonding,which can serve as nucleation sites.Therefore,t ACA can play a cross-linking role.Both the amino and carboxyl groups of c ACA are involved in the formation of intermolecular hydrogen bonds,and in addition to the amino groups forming hydrogen bonds with the perovskite,the carboxyl groups can form coordination bonds with Pb²⁺.These complex interactions prevent c ACA from promoting the nucleation and growth of perovskite.（3）To further improve the crystallization quality of perovskite in p-MPSCs and enhance the device performance,chloroformamidine hydrochloride（Cl-FACl）containing both Cl^-and highly electronegative Cl atom was used to modify Cs_0.1FA_0.9PbI₃ perovskite.It is demonstrated that the Cl-FACl additive can effectively enhance the crystallinity and conductivity of perovskite,significantly suppress the nonradiative recombination of carriers,and lower the Fermi level of perovskite materials,thus increasing the driving force of charge transfer at the perovskite/Ti O₂ interface.To further analyze the role of cations in chlorine-containing additives,the differences in the effectiveness of formamidine hydrochloride（FACl）,2-chloroacetamidine hydrochloride（Cl-Ace Cl）and Cl-FACl were compared.The large steric hindrance of Cl-Ace⁺can affect the phase transition process of perovskite and reduce the crystallinity.Compared with FACl,Cl-FACl is more effective in enhancing perovskite crystallinity and suppressing carrier nonradiative recombination.FACl and Cl-FACl increased the PCE of p-MPSCs from 16.25%to 17.48%and 17.98%,respectively,while Cl-Ace Cl reduced the PCE to 15.47%,confirming the synergistic effect of the anion and cation in Cl-FACl.（4）Based on the gradual optimization of the infiltration and crystallization of the perovskite materials in p-MPSCs,a strategy of using in situ self-polymerization additives to passivate the grain boundaries and improve the device performance was proposed to address the problem of fine perovskite grains with numerous grain boundaries.Taking advantage of the property that 2,5-dibromo-3,4-ethylenedioxythiophene（DBEDOT）can polymerize into poly（3,4-ethylenedioxythiophene）（PEDOT）at low temperature,DBEDOT was introduced into the perovskite precursor solution and polymerized during the annealing process of perovskite.The polymerization product with conjugated structure can facilitate carrier transport and passivate uncoordinated Pb²⁺.Based on this strategy,the charge transport in p-MPSCs is improved and the nonradiative recombination process is suppressed,enhancing the PCE of corresponding devices from 17.16%to 18.20%.