Efficient sky-blue perovskite light-emitting diodes enabled by buried guanidine passivation

The light-emitting efficiencies of blue perovskite light-emitting diodes (PeLEDs) based on quasi-two-dimensional (quasi-2D) halide perovskite emissive layers still lag behind in comparison to their green and red counterparts. The buried interfaces strongly affect the properties of upper solution-processed quasi-2D halide perovskites and the resultant PeLEDs. Herein, it is proposed to passivate the defects of blue quasi-2D perovskites at the buried interfaces by modifying the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) hole-transport layer (HTL) with 4-guanidinobutyric acid (GBA). The GBA-modified PEDOT:PSS can help to passivate the defects of blue quasi-2D perovskites at the buried interfaces through the interaction between the amine groups of GBA and lead ions and enhance the ratios of halide ions and 4-fluorophenylethylammonium bromide to lead ions. Owing to the reduced halogen vacancies and the passivated defects at the buried interfaces, the blue quasi-2D perovskites prepared on the GBA-modified PEDOT:PSS HTL lead to an increased photoluminescence quantum yield (PLQY) of 60.8 %. The corresponding sky blue PeLEDs achieve a maximum light-emitting quantum efficiency of 9.41 % with an emission peak at 488 nm. This work contributes to enhancing the light-emitting performance of blue PeLEDs through the buried interface passivation point of view.