Abstract
Enhanced hole injection is essential to achieve high performance in perovskite light-emitting diodes (LEDs). Here, a strategy is introduced to enhance hole injection by an electric dipole layer. Hopping theory demonstrates electric dipoles between hole injection layer and hole transport layer can enhance hole injection significantly. MoO3 is then chosen as the electric dipole layer between PEDOT:PSS (hole injection layer) and PVK (hole transport layer) to generate electric dipoles due to its deep conduction band level. Theoretical results demonstrate that strong electric fields are produced for efficient hole injection, and recombination rate is substantially increased. Capacitance-voltage analyses further prove efficient hole injection by introducing the electric dipole layer. Based on the proposed electric dipole layer structure, perovskite LEDs achieve a high current efficiency of 72.7 cd A−1, indicating that electric dipole layers are a feasible approach to enhance perovskite LEDs performance.
Highlights
Enhanced hole injection is essential to achieve high performance in perovskite light-emitting diodes (LEDs)
With the advanced device structure of indium tin oxide (ITO)/PEDOT:PSS/MoO3/PVK/ Perovskite/TPBi/LiF/Al, we have fabricated the PeLED with an improved external quantum efficiency (EQE) by 8.7% up to 16.8% and an improved current efficiency (CE) by 37.2 cd A−1 up to 72.7 cd A−1, indicating a feasible approach with the electric dipole layer of MoO3 to achieve a high PeLED performance
To understand the effect of electric dipole on hole transport in PeLEDs, we study a typical hole transport model with the structure of hole injection layer (HIL)/hole transport layer (HTL)
Summary
Enhanced hole injection is essential to achieve high performance in perovskite light-emitting diodes (LEDs). The thickness of the transport layer can be optimized during the film fabrication process by controlling the parameters of spin-coating or evaporation speed and time, which are widely used to obtain the ideal film thickness in fabrication of the devices Besides these methods, charge block layer has been commonly adopted to reduce the major carrier transport rate to balance the charge injection. Introducing an electron block layer at the interface of perovskite/ETL can retard the electron injection and improve the efficiency, while there is a large difference of highest occupied molecular orbital (HOMO) between PEDOT:PSS and PVK, which causes a nonnegligible hole injection barrier and results in a large energy loss and high turn-on voltage[18,19,20]. Doping of HIL and HTL are an effective method to increase their mobility so as to increase the hole injection rate[22,23]
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