Optimization Of Functional Layers Of Perovskite Light-Emitting Diodes And Preparation Of Paper-based Perovskite Light-Emitting Diodes

Organic-inorganic metal halide perovskite materials have been widely applied for the field of optoelectronics due to their high color purity,tunable bandgap,high photo luminescence quantum yield,and low-temperature solution processing in recent years.Currently,the highest efficiency of perovskite light-emitting diodes(PeLEDs)has exceeded 25%.However,most of these high-performance devices were fabricated in a glovebox under inert and dry conditions,which were unfavorable for the future industrialization of PeLED technology.Furthermore,developing a time-efficient and efficient solution-based process for device fabrication is a necessary condition for promoting the industrialization of PeLEDs.In this regard,based on additive engineering,the rheological properties of the solution by incorporating PEO to control the formation of perovskite films were regulated in this article.Additionally,the barrier effect of PEO was used to prevent the degradation of perovskites by water and oxygen in the air.In addition,the transfer printng technique of conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)as a transparent top electrode for light-emitting diodes was explored.Moreover,using cheap and biodegradable paper substrate instead of glass substrate to fabricate flexible perovskite light-emitting diodes was also studied.The main research contents are as follows:(1)Considering the aggregation effect of solvents in functional layer solution film formation,a different solvent with a different boiling point can be added to solve it.Therefore,the uniformity and coverage of the luminescent functional layer of perovskite were enhanced through the optimization of the cavity transport functional layer formation using isopropyl alcohol(IPA),and the addition of polyethylene oxide(PEO)to the precursor solution of methylamine lead bromide(CH3NH3PbBr3).Using a fully solution-based method in air,a low turn-on voltage perovskite light-emitting diode with a PEO-modified perovskite luminescent layer was prepared,and the main reason for the uniform film formation of the PEO-modified perovskite luminescent layer was analyzed.The results showed that the doping of IPA not only improved the uniformity of the hole-transporting layer and provided a good foundation for the film formation of the luminescent layer,but also reduced the energy level difference between PEDOT:PSS and CH3NH3PbBr3 by 0.18 eV,which lowered the turn-on voltage of the device by 0.4 V.The use of PEO improved the resistance of the perovskite luminescent layer to water and oxygen in the air,and limited the size of perovskite crystals,increasing the coverage of the perovskite film.The fabricated device owned a turn-on voltage of 2.4 V,a maximum brightness of 3126 cd m-2,and a maximum current efficiency of 0.65 cd A-1 in air testing.(2)The unevenness of the PEDOT:PSS film formation was restrained by incorporating a high-boiling point solvent,while the conductive property of PEDOT:PSS was improved by incorporating a surface surfactant.By plasma treatment of the PDMS substrate surface,the film-forming effect of the conductive polymer PEDOT:PSS on transfer media was improved.And the thickness of the PEDOT:PSS film was controlled via adjusting the spin-coating speed.The optical transmittance and the electrical conductivity of the PEDOT:PSS films with different thicknesses were also investigated.By transferring the PEDOT:PSS electrode to the device,fabricated a perovskite light-emitting diodes in air was fabricated.The results showed that plasma treatment of PDMS at 30 W power for 60 s produced a PEDOT:PSS film on the surface of the medium with good uniformity and roughness.The optical transmittance of the prepared PEDOT:PSS films was above 77%,and the sheet resistance was below 105 Ω sq-1.The device fabricated using the indirect transfer of the electrode still showed good electroluminescent brightness(1022 cd m-2)in air.(3)By printing UV varnish coating on paper surface,the surface smoothness was improved and the permeability of the paper was reduced.We also used PEO-doped perovskite precursor solution to deposit perovskite film on the paper surface in air,and analyzed the optical properties of the perovskite film on different paper surfaces.Considering the opacity of the paper,a PEDOT:PSS film was transferred as the top transparent electrode layer for the device,and its electrical conductivity and optical transparency were characterized.Finally,a paper-based perovskite light-emitting diode was assembled.The results showed that the UV varnish not only filled the interlaced pores of the fiber-based paper surface,but also further improved the surface smoothness and reduced the permeability of the coated paper,reducing the root mean square roughness of both coated and uncoated papers by over 90%.Meanwhile,the water resistance of the coating on paper was greatly improved,and the paper coating remained intact for 30 s without liquid penetration,and the strength of the paper did not change.A fine,uniform and dense perovskite film with higher quality than the perovskite film on the smooth and flat PET reference substrate was realized by modifying paper surface.