High-performance Perovskite Solar Cells Achieved By Defects Passivation Strategy

Perovskite solar cells（PSCs）have drawn enormous attention due to its advantages,such as superior optoelectronic properties,solution fabrication process,low cost,etc.The efficiency of PSCs enhances from 3.8%to 25.7%during the past decades.While the ionic property and the uncontrollable crystallization process would introduce various defects among the perovskite film.These defects would not only trap the charge carriers to cause the serious nonradiative recombination,but also serve as the pathways for the water and oxygen penetration,which was harmful to the stability of the PSCs devices.Thus,it is highly desirable to conduct the defects passivation engineering to enhance the efficiency and stability of PSCs.In this work,we focus on the defects passivation strategy for the bulk perovskite film and the interface between perovskite layer and the functional layer to enhance the performance of PSCs.The detailed achievements are summarized as follows:1)We incorporated a novel Lewis acid passivator based on the photo-cationic initiator（TPFB）into the perovskite film by the anti-solution process.Firstly,the F in the pentafluorophenyl borate part would form hydrogen bond with MA⁺to slow down the crystallization process thus render the high-quality perovskite film.While the hypervalent iodine part could serve as a Lewis acid to passivate the negatively charged defects to reduce the defects density.Meanwhile,this strategy also enhanced the hydrophobicity.The efficiency was enhanced from 19.35%to 20.41%with TPFB incorporation.We also investigated the universality of the strategy by depositing the TPFB on the surface of the as fabricated perovskite film through the post-processing.Surprisingly,the efficiency raised up to 23.4%.More importantly,the environmental stability was enhanced with TPFB incorporation,the unencapsulated devices could maintain 85%of its initial efficiency after1000 h storage.Finally,we utilized TPFB as the single-dopant to promote the oxidation process of Spiro-OMe TAD,the PSCs device demonstrated enhanced stability based on this strategy.2)We investigated a novel surface passivation strategy by introducing F-PEAI on the surface of the as-fabricated perovskite film directly,rather than forming 2D perovskite.The introduction of F-PEAI could effectively passivate the halide vacancy defects.After the introduction of F-PEAI,the photoluminescence intensity and lifetime were extremely enhanced,indicating the superior defects passivation ability of F-PEAI.At the same time,the hydrophobicity was enhanced due to the introduction of F-PEA⁺.The efficiency of the PSCs devices raised from 18.62%to 19.61%after the F-PEAI treatment,and the unencapsulated devices could maintain 85%of its initial efficiency after storage in ambient environment for500 h.3)We released the interfacial strain and reduce the formation of hydroxyl by introducing the Cs F interlayer between the Sn O₂ ETL and perovskite film.Firstly,the F^-could form the Sn-F bond with the uncoordinated Sn⁴⁺to inhibit the formation of hydroxyl.Secondly,the F^-could interact with the as-formed hydroxyl to reduce the concentration.At the same time,the F^-could chelate with Pb²⁺to form the Pb-F bond,and interact with organic amine cation to form the N-H…F hydrogen bond.While,the Cs⁺could serve as the structural component of lattice unit.The Cs F interlayer resembled anchor layer to tailor the crystallization process and release the interfacial strain.The efficiency of the PSCs devices enhanced from 21.93%to 23.13%after the introduction of Cs F and could maintain 87%of its initial efficiency after storage in ambient environment for 1000 h without encapsulation.4)We investigated a feasible strategy to tailor the crystallization process and enhance the super oxide resistance by introducing the reduced glutathione（GSH）into the perovskite precursor solution.We have confirmed that the strong interaction between GSH and Pb I₂ was formed,thus the perovskite crystallization process was suppressed significantly.At the same time,we verified that the defects formation energy and the activation energy for ion migration was enhanced by the calculation of density functional theory and activation energy measurement,which would inhibit the formation of iodine vacancy defects,thus decrease the sites for oxygen absorption.The GSH could also interact with the as-formed super oxide.Furthermore,we successfully confirmed that the formation of super oxide was extremely restrained by the molecular fluorescent probe.The efficiency of the PSCs devices was enhanced from 21.53%to 22.89%and could maintain 91%of its initial efficiency after storage in ambient environment for 1000 h without encapsulation.