Fabrication And Properties Of Iridium Complex-based Flexible Light-Emitting Electrochemical Cells

Light-emitting electrochemical cells(LEC)shows potential applications in displays and lighting.In comparison with its counterpart organic light-emitting diodes(OLED),LEC is desirable owing to its simpler in structure,solution processable,insensitive to the work function of electrodes and low driving voltage.These advantages are preferable to fulfill the requirements during the encapsulation of LEC and ease in preparation of flexible devices.Ionic transition metal iridium complex materials are commonly used in LEC device structure due to its excellent characteristics such as lower phosphorescence lifetime,high luminescence quantum efficiency and easy color control.To date,studies on the flexible LEC and parameters optimization for device fabrication are rarely reported and will be carried in this work.In order to solve these problems,the works have been carried out as follows:The preliminary study has begun with optimization of preparation parameters such as material preparation,deposition speed and annealing process for iridium complex films.The obtained results indicated that the film demonstrated optimum performance when the concentration of Iridium complex in acetonitrile is 20 mg/ml and spin-coated at 2000 rpm.Then,the film was annealed at 70 ? to achieve 82.6%transmittance in visible region.Subsequently,the fabrication and performance optimization of monochrome LEC based on flexible ITO substrate was studied.The effect of ion liquid BMIMPF6 at different doping rate on the orange flexible LEC show that the device attained optimum performance when the doping rate of BMIMPF6 is 20%.The flexible LEC based on iridium complex Y1 and Y2 show the efficiency as high as 11.6 cd/A and 16 cd/A at 6V,respectively,for orange electroluminescence.Next,the electrical characterization was performed to the flexible blue-green LEC.It is observed that the brightness would increase and response time would decrease when the voltage was increased,but the stability of the device would be deteriorated at the same time.The flexible LEC based on iridium complex B1 and B2 show the maximum efficiency as high as 10.72 cd/A and 16 cd/A,respectively,for blue-green electroluminescence when the doping rate of BMIMPF6 is 20%.Lastly,the fabrication and performance optimization of flexible white LEC was carried out.A flexible white LEC based on blue material PFO doping with orange iridium complex Y1 was constructed.When the ratio of PFO:Y1 is 70:1,the color coordinates is(0.31,0.34)which is close to the standard white point and exhibited an efficiency of 0.92cd/A.Meanwhile,a flexible white LEC based on blue-green iridium complex B2 doping with red iridium complex R1 was also conducted and found that when the ratio of B2:R1 is 80:1,the fabricated device showed white electroluminescence with high efficiency of 9.8 cd/A at 7 V with CIE coordinates of(0.43,0.42),and the maximum luminance is 500 cd/m2.In conclusion,the fabrication of iridium complex-based flexible light-emitting electrochemical cells was studied in detail.High quality orange,blue-green and white flexible LEC were fabricated successfully.This study suggested that flexible LEC may find potential applications in displays and lighting.