Interface Engineering On Organic Light-emitting Diodes And Perovskite Light-emitting Diodes

Organic light-emitting diodes(OLEDs)have been successfully commercialized in display and solid-state lighting applications,due to OLEDs' advantages of self-emission,fast response,multicolor,etc.In recent years,perovskite light-emitting diodes using metal halide perovskite as the light-emitting material have attracted much attention.Both types of light-emitting diodes are thin-film devices with a multilayer structure,in which the interfaces limit the performance of the device.Therefore,interface engineering is critical to improve the device performance.For conjugated polymer based OLEDs,most polymers have high LUMO energy levels,there is generally a large barrier between the polymer light emitting layer and the cathode,making electron injection difficult.To reduce the electron injection barrier,we introduced ethanolamine solvent between the light-emitting layer based on SY-PPV and the metal cathode to modify the interface and achieve high-efficiency yellow-emitting device.Compared to the unmodified light-emitting device,the device modified with ethanolamine improves the maximum current efficiency from 2.31 cd/A to 9.41 cd/A.It's found that ethanolamine solvent forms a weak interface dipole,which reduces the electron injection barrier.Moreover,ethanolamine solvent permeates through the light-emitting layer to modify the hole transport layer PEDOT:PSS.The modified PEDOT:PSS suppresses the injection of holes,which balances the electron and hole carriers,thus enhancing the device performance.In addition,the surface treatment of ethanolamine on the perovskite may also have certain guiding significance.On the one hand,when a kind of small molecule with an amine group treats perovskite,it is very likely to play a role in surface passivation;on the other hand,when a small molecule with an amine group treats perovskite,the surface of the perovskite may form two-dimensional perovskite,which helps to increase exciton binding energy.For perovskite light-emitting diodes,the hole transport layer PEDOT:PSS 4083 is mixed with alcohols.Compared to devices with pristine PEDOT:PSS,the device with treated PEDOT:PSS enhances the current efficiency 2.65 times,and EQE 2.9 times.The current efficiency reaches 33.8 cd/A,while the EQE reaches 8.368%.The mechanisms responsible for device performance enhancement are:(1)Improvement of hole injection characteristics.Treating PEDOT:PSS 4083 with alcohol-doped solvent can partially remove the insulating PSS to help hole injection.In addition,the work function of the modified PEDOT:PSS 4083 is increased,thus lowering the hole injection barrier.(2)Improvement of the morphology and the crystal quality of perovskite film.The perovskite film deposited on the modified PEDOT:PSS film has better surface coverage,smaller grain size,and less pinholes.(3)Dimensional change in perovskite.After the treatment of PEDOT:PSS,the dimensional changes from threedimensional to quasi two-dimensional structure,which causes quantum confinement effects,increases the exciton binding energy,promotes radiation recombination,reduces exciton quenching,and ultimately improve device performance.