Fig. 1. Configuration and energy level diagram of light-emitting devices. (a) Configuration; (b) energy level

Fig. 2. Crystal structures of perovskite materials. (a) XRD patterns; (b) enlarged version of the (100) diffraction peak region; (c) substitution of MA⁺ in the MAPbBr₃ core by EA⁺; (d) tolerance factor of MA_xEA_(1-x)PbBr₃ as a function of the MA⁺ proportion

Fig. 3. Morphologies of perovskite samples (intest show high-resolution SEM images). (a) MAPbBr₃, top-view; (b) 5∶1 sample, top-view; (c) 2∶1 sample, top-view; (d) 1∶2 sample, top-view; (e) cross-sectional SEM image of the 2∶1 sample

Fig. 4. Photo-physics properties of the perovskite samples. (a) UV-vis absorption spectra; (b) steady-state PL spectra, insets show the images of the 2∶1 sample under white (left) and UV light (right); the MAPbBr₃ and 2∶1 samples for (c) UPS spectra, (d) time-resolved luminescence decay curves, (e) I-V characteristics of hole-dominated devices, and (f) photo-stability measurements

Fig. 5. Properties of light-emitting devices. (a) J-L-V characteristics; (b) EQE-voltage curves; (c) power efficiency-voltage plots; (d) EL spectra, inset is a photo of 2 ∶1 device; (e) operational stability measurements of the MAPbBr₃ and 2∶1 devices

Table 1. Fitting parameters of the time-resolved luminescence decay characteristics of the samples

Table 2. Detailed properties of light-emitting devices