# Tightly Compacted Perovskite Laminates on Flexible Substrates via Hot-Pressing
## 3 Results and Discussion
The relative intensity was taken as the ratio of the intensity of one peak to the total intensities of the three main peaks at 15.2\({}^{\circ}\), 21.5\({}^{\circ}\), and 30.7\({}^{\circ}\). The relative intensities of the dominant diffraction peaks corresponding to the (100), (110), and (200) lattice planes also varied significantly, proving recrystallization of the laminated perovskites [20; 33]. It was found that the relative intensities of the (100) and (200) diffraction planes increased monotonically with increasing imposed pressure, while the intensity of the (110) plane decreased after lamination. The lamination induces a change in crystallinity from a (110)-dominant scenario to a (100)- and (200)-dominant scenario. When compared with the heated samples without applying pressure, the pressure-induced recrystallization was much more significant and preferred crystallization orientation along the (100) and (200) planes. It was reported that the (100) peaks in perovskites have a high relationship with heavy atoms Pb and Br with long-range ordered packing [16] and are able to provide efficient charge transport [34; 35]. XRD provided evidence of substantial recrystallization and an overall improved crystal quality upon lamination. These results reveal explicitly that changes in FWHM are mainly derived from heat and changes in crystal orientation originating from pressure. When heated at a high temperature, the perovskite softens and the external pressure applied to the soft perovskite layer leads to recrystallization. Under the synergistically effect of temperature and pressure, the interatomic distances of perovskite can be adjusted, and thus, the crystallographic symmetry can be affected. As to the optical properties of perovskite laminates, the CsPbBr\({}_{3}\) films show an absorption edge at 516 nm and a bright green PL emission centered at 528 nm under ambient conditions, as shown in Figure 3a,b. The absorption and PL spectral profiles remained almost unchanged before and after lamination. This behavior under MPa-scale pressure is consistent with prior work [21], which means that a comparatively low compressive pressure is not able to lead to strong lattice distortions in the lead halide perovskite crystallographic structure. Although the band gap was not affected after lamination, the thin film morphology and perovskite crystallinity changed, which consequently affected the PLQY. The PLQY values of the perovskite laminates slightly decreased, whereas those of the perovskite films heated without applying pressure decreased severely. Specifically, the absolute PLQY value was reduced from 40% for the pristine CsPbBr\({}_{3}\) thin film to 35% for the sample laminated at 90 \({}^{\circ}\)C and 10 MPa. On the contrary, the value dropped down to 12% for the sample only heated at 90 \({}^{\circ}\)C. Table 1 summarizes the PLQY values of pristine CsPbBr\({}_{3}\) film and the laminates prepared under different conditions. To investigate the photophysical properties of the perovskite films after lamination, time-resolved photoluminescence (TRPL) decay profiles were measured, and the results are shown in Figure 3c. The PL lifetimes were obtained by  
Figure 3: (**a**) Absorption and (**b**) photoluminescence (PL) spectra of the pristine CsPbBr\({}_{3}\) film and the laminates prepared under different conditions. (**c**) Time-resolved photoluminescence of the pristine CsPbBr\({}_{3}\) thin film and the laminates prepared at 90 \({}^{\circ}\)C and 10 MPa. fitting the decay curves with a biexponential decay function including a fast decay component (\(\tau_{1}\)) and a slow decay component (\(\tau_{2}\)). The laminated perovskite film exhibits biexponential decays with a \(\tau_{1}\) value of 0.52 ns and a \(\tau_{2}\) value of 4.90 ns, while the pristine film has slightly larger \(\tau_{1}\) and \(\tau_{2}\) values (\(\tau_{1}\) = 0.57 ns, \(\tau_{2}\) = 5.33 ns).