Extended Data Fig. 7: Characterization of our perovskite films and LEDs at different precursor concentrations.

a, SEM images. The scale bars represent 1 μm. As the precursor concentration increases (shown in the top left corner of each image), the size of the crystallites increases and the crystallites become more tightly packed. b, XRD spectra. c, Excitation-intensity-dependent PLQEs. The 7 wt.% film shows the highest PLQEs. d, Dependence of current density on driving voltage. The leakage currents of the devices decrease as the precursor solution becomes more concentrated. e, Dependence of radiance on the driving voltage. As the precursor concentration increases, the turn-on voltage increases and the radiance decreases, probably owing to the poor charge transport of thicker film. f, EQE plotted against current density. g, Peak EQE versus precursor concentration. Error bars correspond to the standard deviation. When the concentration exceeds 10 wt.% the EQE decreases, probably because of a reduced outcoupling-enhancement effect and poor charge transport.