Study On The Control Of Ternary Solvent Ink And Pixel Array Devices For Inkjet Printing

As an emerging technology with the advantages of high material utilization,mask-free,compatibility with flexible plastic substrates,high spatial resolution,good flexibility and excellent reliability,inkjet printing enables a new generation of printable,low cost,large area,high performance lighting and displaying devices based on light-emitting diode（LED）by combining with organic small molecule materials and perovskite materials.However,the coffee ring effect generated during inkjet printing due to the viscosity,surface tension and boiling point of the ink often leads to uneven thickness and poor surface morphology of the printed films,which deteriorates the device performance.In addition,when inkjet printing in pixels,the droplet contact line tends to shrink to the edges of the pixel during evaporation due to the high surface energy or high surface wettability of the bank of the pixel,forming unevenly deposited films with thick edges and thin centres in the pixel.In order to improve the quality of inkjet printing films and improve the performance of inkjet-printed devices,this thesis mainly focuses on the ink formula and film formation mechanism of inkjet printing,and focuses on the main methods of achieving uniform film layers for inkjet printing organic small molecule emitting inks and perovskite quantum dots inks.By adjusting the formulation of the ternary mixed-host emitting layer,a multi-layer inkjet printed OLED was achieved using ternary solvent emissive inks in a pixel array.In addition,by regulating the ternary solvent of blue perovskite quantum dot ink,ink jet printing with a uniform film was achieved.Details of the thesis are as follows:（1）Ternary mixed-host emitting formulation modulation for the preparation of green phosphorescent OLEDs.Polyvinylcarbazole（PVK）and organic small molecule material 4,4’-bis（9-carbazole）biphenyl（CBP）as good hole-transporting hosts,bipolar material of 2,6-bis（3-（carbazole-9-yl）phenyl）pyridine（26DCz PPy）and electron transport material of（1,3,5-triazine-2,4,6-triyl）tris（benzene-3,1-diyl）tris（diphenylphosphine oxide）（PO-T2T）or 2,7-bis（diphenylphosphinyl）-9,9’-spirobifluorene（SPPO13）were chosen as the ternary mixed host to prepare green phosphorescent emitting layer by doping the green phosphorescent Ir（ppy）₂（acac）as the guest.The effects of different mixed-host materials and ternary mixed-host ratios on the balance of carrier injection and transport and device performance were compared.Finally,due to the ability of both hole and electron transport and the broadened exciton recombination region in the ternary host of PVK:CBP:26Dcz PPy,the lowest turn-on voltage of 4 V and the optimal current efficiency of 27.6cd/A were achieved.（2）Inkjet-printed OLED pixel arrays were prepared with emissive ink dissolved in ternary solvents.Based on the emitting material of PVK:CBP:26DCz PPy:Ir（ppy）₂（acac）,chlorobenzene（CB）:chloronaphthalene（CN）binary solvent and CB:CN:o-dichlorobenzene（ODCB）ternary solvent-based emissive inks were prepared with CB,ODCB and CN solvents.By adjusting the ink viscosity,surface tension and other parameters,comparing the film formation mechanism of the binary and ternary solvent inks,and changing the ratio of the ternary solvent,the coffee ring-free inkjet-printed organic small molecule emitting film was achieved,and the problem of the ink absorbed by the bank of the pixel was solved,with which the multilayer printed films were achieved in pixel and efficient,stable and uniform inkjet printed OLED pixel arrays were ultimately fabricated.（3）Ink formulation and printed film preparation of blue perovskite quantum dots were explored.Butyl benzoate（BB）,cyclohexylbenzene（CHB）,o-dichlorobenzene（ODCB）and cyclohexanone（CYC）were introduced in ethyl acetate（EA）as co-solvents to prepare inkjet-printed emitting inks.By comparing the coffee ring effect of inkjet-printed film with different binary solvent systems such as EA:CHB,EA:BB,EA:ODCB,or ternary solvent systems such as EA:BB:ODCB,EA:CYC:BB,on different substrates such as PEDOT:PSS,PVK:PMA,PTAA and PTAA:PMA,a coffee ring-free blue perovskite quantum dot film was finally achieved on the PVK:PMA substrate using a ternary solvent of EA:BB:ODCB and EA:BB:CYC,and inkjet printing of blue Pe QLED were ultimately fabricated.