Interface Modification Of Solution-Processed Perovskite Light-Emitting Diodes And Related Studies

Since metal halide perovskite materials have high carrier mobility,solution-processable,high photoluminescent efficiency,narrow luminescent spectrum,and the ability to easily tune emitting color,the research and development on them in the field of optoelectronics has made tremendous progress recently.With multi-layer thin-film device structure,various key electronic processes including carrier injection,and exciton recombination,take place at the HTL/EML or EML/ETL interfaces.Therefore,the interface is critical to the performance of the perovskite optoelectronic devices.The morphology of the perovskite film greatly affects the optical/electrical properties at the interface.For example,the grain size and film defects affect the exciton radiation recombination,and the discontinuity of the luminescent layer leads to an increase in leakage current of the device.Adjusting the ratio of the two components is a simple method to improve the film morphology and quality of perovskite.Here,the morphology and crystallization of perovskite film with different FABr:PbBr₂ molar ratio,and its optical properties were systematically studied.It is found that the molar ratio of FABr:PbBr₂ in the precursor solution is crucial to the crystallinity,coverage and grain size of the perovskite film.When FABr:PbBr₂ is 1:1,the film is discontinuous and the crystal grains are large.At the same time,due to the Br loss caused by the incomplete reaction between FABr and PbBr₂,the metallic Pb in the FAPbBr₃ film was excessive.Excess metallic Pb may serve as a kind of quenching site and result in increasing the non-radiative recombination rate and reducing the radiation recombination rate.When the precursor ratio is changed,excess FABr not only improves film continuity and crystallinity,but also increases the PL intensity and exciton lifetime of the film.Finally,the maximum current efficiency of the PeLEDs is increased from0.02 cd/A to 0.58 cd/A by optimizing the molar ratio of organic and inorganic components in the precursor solution.To improve the device performance,the hole transport layer and the electron transport layer have been examined.For FAPbBr₃-based perovskite light emitting diodes,the maximum brightness(L_max)increases from 7.78×10³ cd/m² to 3.09×10⁴ cd/m² by using PEDOT:PSS8000 instead of PEDOT:PSS 4083,and the maximum current efficiency(CE_max)increases from 1.3 cd/A to 6.3 cd/A,and the maximum external quantum efficiency(EQE_max)is enhanced from 0.11%to 1.17%.The performance enhancement is attribute to the reduced hole current density,which comes from the insulating poly（styrene sulfonate）（PSS）-rich layer at 8000 surface.The insulating layer supresses hole current to improve charge balance and reduce exciton quenching at the interface.To further balance the hole current,a smaller particle size ZnO NPs with higher mobility and higher work function is used as the ETL to increase the electron current and reduce the exciton dissociation at the interface.The CE_maxax increases to 21.3 cd/A,the EQE_max reaches 4.66%,the L_max increases to 1.09×10⁵ cd/m²,and the maximum power efficiency(PE_max)reaches 22.3 lm/W.Inkjet-printing solvent onto insulating polymer layer is employed to in situ build microgrooves as bank structures in the application of solution-processed OLED display.The inkjet-etching process not only eliminates the photolithography’s shadow mask and photo exposure,but also is capable of construct the bank structures on any functional layer.The orthogonal solubility between CYTOP polymer and organic layer avoids any solvent erosion.A pixelated display is successfully fabricated by inkjet-printing blue-emitting polymer into inkjet-etched CYTOP microgrooves with pixel resolution of 140 lines per inch.Forming the bank structure in situ on any layer as needed offers more choices to design new panel structure,device architecture,and deposition methods.