Highly efficient inkjet printed flexible organic light-emitting diodes with hybrid hole injection layer

Highly efficient flexible organic light-emitting diodes (OLEDs) fabricated by utilizing inkjet printing technique are demonstrated in this work. A strategy of hybrid hole injection layer is employed to improve the device efficiency, where the polyethylene glycol (PEG) is used to modify the energy level and conductivity of the conventional hole injection layer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), which regulates the amount of holes entering the organic light-emitting layer, realizes the injection balance of carriers, and nearly doubles the green device efficiency with the record high maximum external quantum efficiency (EQE) of 9.45% and the current efficiency of 28 cd/A. Moreover, the introduction of PEG improves the mechanical properties of PEDOT: PSS and improves the bending resistance of the device. A highly efficient flexible white OLED device is realized by using inkjet printing based on the PEG-modified PEDOT:PSS hole injection layer, achieving the maximum EQE of 4.8%. In addition, a 1-inch white OLED array device is realized on the flexible substrate, which further confirm the feasibility of large-scale production for inkjet printed flexible devices.