Passivation Of Perovskites With Amino Acid To Boost Efficiency And Stability Of Perovskite Solar Cells

The power conversion efficiencies?PCE?of perovskite solar cells?PSCs?based on these lead halide perovskites have risen from an initial 3.8%to the highest-level 25.2%within the past few years.Organic-inorganic hybrid perovskites have intrigued great interests as promising candidates for the third generation solar cells due to their tuneable composition with appealing properties,such as large absorption coefficient,small exciton binding energy,long carrier diffusion length,etc.Firstly,we analyzed the problem that devices based on hole layer poly[bis?4-phenyl??2,4,6-trimethylphenyl?amine]?PTAA?usually show a lower fill factor?FF?and proposed corresponding solutions.We modified the device by doping PTAA with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane?F₄-TCNQ?,thus successfully improving the device's FF.Then we conducted further research on several common problems in the MA/FA system,e.g.,yellow phase,poor film quality,unstable device,etc.The introduction of Cs⁺in the perovskite material of the MA/FA system to prepare a three-cation organic-inorganic hybrid perovskite can adjust the tolerance factor of the perovskite crystals,thereby suppress the yellow phase impurities in the MA/FA system and improve the crystallinity of the film.The pinholes in the perovskite film and lead iodide crystals on the surface of the film are also reduced.On the basis of this work,the quality of the film layer has been greatly improved,and the efficiency and stability of the device have been greatly enhanced.Secondly,compared with the traditional hole transport layer,the main contribution of PTAA is to boost a high open-circuit voltage(V_oc)PSCs.But the hydrophobic PTAA is less affiliative to the polar perovskite precursor solution and it is tricky to achieve high quality perovskite films on top of PTAA.Therefore,the perovskite grown on the hydrophobic PTAA layer also leads to inferior device reproducibility.To this end,we doped the appropriate amount of 2-phenylethylamine hydroiodide?PEAI?in the pre-wetting solution N,N-dimethylformamide?DMF?,which improved the film-forming quality of perovskite and enhanced the repeatability and efficiency of our PSCs.Finally,considering the performance and stability of PSCs are closely related to charged defects at the surface and grain boundary of perovskite films.Additive doping has been proven to be highly effective in the passivation of these defects.Herein,amino acid?s?-?-?-4-amino-2-hydroxybutyric acid?AHBA?with trifunctional groups was proposed as an effective multisite passivator and crosslinker to greatly improve optoelectronic performance and stability of perovskite films.It was proved that the functional groups of amino and hydroxyl from AHBA can anchor the iodide anions of PbI₆^4- octahedra,while the carboxyl moiety can coordinate with the lead cations,all of which contribute to high-quality perovskite film with reduced trap state densities.The addition of AHBA also delays the crystallization of perovskites and involves more FA⁺and Pb²⁺in precursor solution to form full coverage,low defect density and high crystallinity perovskite films with increasing grain sizes.More importantly,the moderate AHBA doping stabilizes the perovskite crystal structure via impeding the loss of surface Br^- and ion migration.As a result,both efficiency and lifetime were significantly enhanced in planar heterojunction PSCs.The champion device showed an efficiency of20.31% and retains over 94% of initial efficiency after 60 days of storage.