Enhancing Performance of Perovskite Nanocrystal Light-Emitting Diodes with Perfluorinated Ionomer and PEDOT:PSS

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) stands as a prominent hole transport layer (HTL) in perovskite light-emitting diodes (LEDs), known for its remarkable electrical conductivity and light transmittance. However, its electron-blocking properties have shown limitations in achieving optimal charge balance by allowing excessive electron transport. To overcome this challenge, we introduce poly(triarylamine) (PTAA) as an intermediate HTL material between the PEDOT:PSS layer and the perovskite emission layer. By leveraging PTAA's higher lowest unoccupied molecular orbital (LUMO) level of 1.8 eV compared to PEDOT:PSS, a substantial energy barrier is established. This energy barrier effectively traps electrons within the emission layer, elevating radiative recombination rates and consequently enhancing overall efficiency. The notable LUMO energy gap of approximately 1.7 eV between PTAA and CsPbBr 3 further contributes to efficient electron confinement. To optimize hole injection and promote charge balance, we address the highest occupied molecular orbital (HOMO) level mismatch between PEDOT:PSS and PTAA. This is achieved by incorporating perfluorinated ionomer (PFI) into PEDOT:PSS, inducing a band bending effect. The resulting energy level alignment leads to improved device performance. Experimental validation of this energy level engineering strategy in light-emitting diodes (LEDs) demonstrates substantial enhancements. The external quantum efficiency (EQE) achieves a remarkable 2.8-fold increase, advancing from 1.07% to 2.81%, when compared to devices employing PEDOT:PSS alone. Moreover, the current efficiency (CE) experiences a 2.5-fold augmentation, surging from 3.74 cd/A to 9.35 cd/A. The luminance levels soar by an impressive 11.3-fold, ascending from 1,745 cd/m 2 to an impressive 19,780 cd/m 2 .