Fig. 1. (Color online) (a) Optical images of synthesized CsCu₂I₃ powder under natural light and excited by ultraviolet light. (b) PLQY of the CsCu₂I₃ powder.

Fig. 2. (Color online) (a) XRD patterns of the CsCu₂I₃ film and powder. (b) Schematic of CsCu₂I₃ crystal structure. (c) PLE and PL spectra of the CsCu₂I₃ film. (d) Schematic of the energy level structure of STE.

Fig. 3. (Color online) (a) Structure of CsCu₂I₃ Pe-LED. (b) Schematic of VBD for CsCu₂I₃ film. (c) SEM image of CsCu₂I₃ film. (d) Energy level diagram of CsCu₂I₃ device.

Fig. 4. (Color online) (a) Current density–voltage (J–V) and luminance–voltage (L–V) curves of the CsCu₂I₃ Pe-LED. (b) EQE curve of the CsCu₂I₃ Pe-LED. (c) The CIE color coordinate of the CsCu₂I₃ PeLED.