Enhanced Optoelectronic Properties of Green Perovskite Light-Emitting Diodes by Amino Acid-Doped PEDOT:PSS

Halide perovskites are promising materials for light-emitting diodes (LEDs) applications owing to their excellent optoelectronic properties such as long carrier diffusion length, high quantum yield, and facile bandgap tunability. Additionally, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is commonly used as hole transport layer (HTL) in perovskite electronic devices owing to its high hole mobility, solution processability, and optical transparency. However, PEDOT:PSS can potentially degrade the adjacent layers owing to its acidic nature arising from a sulfonic acid group. Furthermore, the electrical conductivity and light emission characteristic of upper perovskite layer decrease due to phase transition from the crystalline phase to an undesired hydrated phase and decomposition of perovskite caused by the moisture absorbed by PSS chains from environment. Therefore, the acidic and hygroscopic properties of PEDOT:PSS reduce the operational stability and lifetime of perovskite LEDs (PeLEDs).<br/>Herein, we report the pH neutralization of PEDOT:PSS by adding basic amino acids, which are arginine, lysine, and asparagine. The addition of amino acids can not only modulate the pH of PEDOT:PSS, but also provide nucleation sites to perovskite crystals, and passivate the defects at the interface of PEDOT:PSS and perovskite. Thus, the addition of amino acids results in enhanced stability and photoluminescence quantum yield of the perovskite nanocrystalline layer. When the amino acid-doped PEDOT:PSS is adopted as HTL layer in PeLEDs, the external quantum efficiency (EQE) of green-emitting PeLEDs (λ=518 nm) is improved from 8.99 to 11.96 % without a shift of electroluminescence spectrum. These results demonstrate that the aforementioned disadvantages of PEDOT:PSS can be overcome, expanding the scope of application of PEDOT:PSS as HTL.