Resurfacing mixed-halide perovskite nanocrystal for efficient and spectral stable pure-red light-emitting diodes

Light emitting diode based on perovskite nanocrystal (PeLED) has attracted widespread attention and achieved rapid advancements in recent years. However, pure-red PeLEDs meeting the Rec. 2020 standard still suffer considerable challenge, especially spectral instability. Here, we reported high efficiency and stable pure-red PeLEDs based on guanidine thiocyanate (GASCN) resurfaced CsPb(Br/I)3 NCs. Theoretical simulation and experimental results confirm the GA+ and SCN- occupy A site and X site on NCs surface respectively. The abundant -NH2 of GA+ can form hydrogen bonds with the halide atoms on NCs surface, and pseudohalogen SCNform stronger bonding with Pb2+, thus inhibiting halide ion migration. The short chain GA+ and SCN- not only boost the optical properties and phase stability of mixed-halide CsPb(Br/I)3 NCs but also enhance electrical coupling of NCs film. The GASCN-NC film exhibits 2.9-fold higher in-plane mobility and 1.65-fold higher out of plane hole mobility. The improved electrical coupling leading to the more balanced carrier transport in LED device. Benefiting from the surface reconstruction by GASCN, the PeLED devices exhibit pure-red emission at 640 nm with high external quantum efficiencies (EQE) of 21.34 % and outstanding spectral stability.