Research On Dion-jacobson Perovskite And Light-emitting Diodes Based On The Spacer Cation Of P-dimethylammonium

Currently,the research on Ruddlesden-Popper（RP）perovskites as well as the light-emitting diodes has been mature,while the research on Dion-Jacobson（DJ）perovskites as well as the light-emitting diodes are few!In DJ perovskites,inorganic layers are sandwiched by spacer cations at both sides,while adjacent inorganic layers are connected by only one layer of spacer cations.Therefore,van der Waals gaps no longer exist,endowing DJ perovskites enhanced structural stability.DJ perovskites are promising to improve the operational and humidity stability of perovskite photoelectric devices,while the current efficiency of DJ perovskite light-emitting diodes is still relatively low at present.In this paper,the current efficiency of green DJ perovskite light-emitting diodes is increased from 3.4 cd/A to 68.1 cd/A systematically in three steps.The main research content is:the phase formation mechanism of DJ perovskite with p-dimethylammonium(PHDMA²⁺)as the spacer cation,FA⁺as the A site cation is investigated and revealed in depth for the first time,then excess formamidinium bromide（FABr）is incorporated to adjust the phase distribution,improve the surface morphology,passivate the defects of DJ perovskite film,thus improving the current efficiency of the devices;then based on the DJ perovskite with FA⁺as the A site cation,cesium bromide（that is Cs⁺）and amino acid（5-AVA）additive are sequentially incorporated to further adjust the phase distribution,improve the surface morphology,passivate the defects of DJ perovskite film,thus improving the current efficiency of the devices.The detailed research content is shown below:（1）Through characterization of X-ray diffraction,steady-state UV-vis absorption spectra,steady-state photoluminescence（PL）spectra and scanning electron microscope（SEM）,the phase formation mechanism of DJ perovskite with PHDMA²⁺as the spacer cation,FA⁺as the A site cation is investigated and revealed in depth:there is almost only n₁ domain and trace amount of large n domain in the perovskite film without annealing,while the n₁ domain is gradually transformed into n₂ domain and large n domain during the annealing process.Base on this mechanism,compositional engineering of A site cation（that is incorporating excess FABr）is put forward.It can be proved by the experimental results that incorporating excess FABr could not only adjust the phase distribution（promote the transformation of n₁ domain into n₂ and larger n domain during the annealing process）,but also improve the surface morphology and passivate the defects of DJ perovskite film,thus improving the current efficiency of the devices.The current efficiency of control device with stoichiometric ratio of n=5 is only 3.4 cd/A.While the current efficiency of 20FA device is improved to 18.1 cd/A after incorporating excess 20%FABr.（2）Based on the DJ perovskite with FA⁺as the A site cation,mixed A site cation engineering is put forward:Cs⁺is incorporated to replace part of FA⁺,then the DJ perovskite film and light-emitting diodes with mixed A site cation of Cs⁺and FA⁺are prepared.It can be proved by the experimental results that it could adjust the tolerance factor,reduce the phase formation energy of DJ perovskite,and adjust the phase distribution,improve the surface morphology of DJ perovskite film,thus improving the current efficiency of the devices.The DJ perovskite film with narrower phase distribution,less defect density,denser surface morphology and higher carrier mobility is obtained by incorporating Cs⁺to replace part of FA⁺.And the current efficiency of the devices is increased from18.1 cd/A to 25.3 cd/A.Finally,the passivated device with a current efficiency of 42.1 cd/A,an external quantum efficiency of 10.5%,a maximum luminance of 7845 cd/m² are obtained by anti-solvent additive engineering（Lewis-base passivation agent of TPBi is dissolved in the Chlorobenzene of the mixed anti-solvent）.（3）Since the anti-solvent additive engineering is difficult to achieve,based on DJ perovskite with mixed A site cation of Cs⁺and FA⁺,the additive engineering is put forward and 5-aminopentanoic acid（5-AVA）is directly incorporated into the perovskite precursor.5-AVA has both functional groups of amino and carboxyl:the amino group interacts with metal halide octahedron through hydrogen bonding,and the carboxyl group at the other end can interact with unsaturated lead ions through coordination of oxygen atom,thus building a bridge for energy transfer,promoting the energy coupling and achieving more efficient energy transfer between adjacent perovskite phases.The coordination between oxygen atoms of carboxyl and unsaturated lead ions effectively passivates the defects of halide（Br^-）vacancy,reduces the defect density and inhibits the formation of metallic lead.It can be proved by the experimental results that incorporating 5-AVA also could improve the crystallinity,adjust the phase distribution and improve the surface morphology of the DJ perovskite film by adjusting the supersaturated crystallization kinetics.The DJ perovskite film with narrower phase distribution,less defect density,denser surface morphology and higher carrier mobility is obtained by incorporating 5-AVA.And the current efficiency of the devices is increased to 68.1cd/A（EQE=17.1%）.