It is widely reported that MAPbBr
3 films comprising PbBr
2:MABr= 1:1.0 always exhibit poor surface coverage and low PLQYs. This is mostly attributed to the existence of a large number of Br vacancies, which serve as nonradiative recombination centers [
28,
29]. Small amounts of MABr additive could increase the content of Br
− and reduce Br vacancies, whereas large amounts of additives will induce the formation of other impurity phases. We attempted to eliminate the Br vacancies by adding excess MABr to the MAPbBr
3. We tuned the molar ratio of PbBr
2:MABr from 1:1.0 to 1:1.3, and the corresponding histograms of peak current efficiency (CE) data are shown in Fig. 1(a). A remarkable CE enhancement in MAPbBr
3 with excess MABr is observed, which is optimized at the molar ratio of PbBr
2:MABr = 1:1.1 (denoted as MAPbBr
3-excess hereafter). Figure 1(b) shows the steady-state PL spectra of the corresponding perovskite films, and the inset is an image of the perovskite films under UV illumination (365 nm). The MAPbBr
3-excess film shows a much higher PL intensity than that of the MAPbBr
3 film, indicating reduced Br vacancies in the MAPbBr
3-excess film. We further compared the surface morphology of the films through SEM. As shown in Fig. 1(c), the MAPbBr
3 film exhibits poor surface morphology with high density of pinholes. On the contrary, as shown in Fig. 1(d), the MAPbBr
3-excess film exhibits a uniform surface with fewer pinholes, where the excess MABr additive increases the concentration of MA
+ and Br
− ions and promotes generation of crystal nuclei to form a high-quality perovskite film. Figure 1(e) presents the corresponding XRD patterns, in which the diffraction peaks of MAPbBr
3 film and MAPbBr
3-excess film are nearly the same, indicating that excess MABr does not change the crystal structure. After preliminary optimization of the composition of the perovskite, we prepared Pero-LEDs devices to evaluate the device performance. Figure 1(f) shows the typical current density
–luminance
–voltage (
J–L–V) curves of the Pero-LEDs based on these two perovskites, from which we see that the luminance of the MAPbBr
3-excess device is significantly higher than that of the MAPbBr
3 device. In particular, when the applied voltage exceeds approximately 6.5 V, the MAPbBr
3 device with poor film quality deteriorates, leading to a decrease in current density. On the contrary, the MAPbBr
3-excess device with fewer defects degrades more gradually and the current density continues increasing to 7.0 V. The maximum CE of the MAPbBr
3 and MAPbBr
3-excess devices are 0.149 and 2.46 cd/A, respectively. These results indicate that an excess of MABr can reduce the intrinsic defects and pinholes of MAPbBr
3 films, enhancing the device performance of Pero-LEDs.