Low driving voltage and enhanced performance of solution-processed blue flexible organic light-emitting diode with PTAA/AgNWs/PTAA composite hole injection layers

The composite hole injection layers (c-HILs) PTAA/AgNWs/PTAA were introduced into solution-processed blue flexible organic light-emitting diode (FOLED) to improve the hole injection ability, further to lower the driving voltage and enhance the device's performance. By optimizing the c-HILs, the optimal FOLED has been achieved with a maximum luminance of 6051 cd m−2 at 9 V and a maximum current efficiency of 1.76 cd A−1, which are increased by 45% and 75% compared to that of the control device without c-HILs. Meanwhile, the optimal device presents the low turn-on voltage of 2.7 V at 1 cd m−2 and driving voltage of 6.0 V at 1000 cd m−2, which are decreased by 0.4 V and 1.9 V compared to that of the control device. The electroluminescent performance enhancement of FOLED is attributed to that the introduction of c-HILs can decrease the hole injection barrier and improve the hole injection ability, which will result in the balanced carrier recombination in emitting layer. Moreover, we analysed the electrical and morphological characteristics of c-HILs, and investigated the mechanism by energy level analysis and impedance spectroscopy.