# Solution Processed Polymer-ABX\({}_{4}\) Perovskite-Like Microcavities
## 3 Results and Discussion
Employing a start-to-end solution processing method allowed us to easily modify structure properties by simple variation of the deposition conditions such as spin-coating rotation speed and concentration of the polymer solution. To better overlap the maxim emission intensity of (EDBE)PbCl4 and PBG, we tuned the latter at 545 nm, a slightly larger wavelength with respect to the sample described above, and the cavity mode at 515 nm, on the short wavelength side of the PBG feature (Figure 3a). Such variations were achieved by decreasing the rotation speed during the deposition of the polymer thin films. The transmittance spectrum of Figure 3a confirms the reproducibility of the fabrication processes, in fact, in both the samples, transmittance values at the PBG are comparable, and the background appears affected by light diffusion, as indicated by the low transmittance values and by the lack of interference fringes. Figure 3a displays the fluorescence spectrum of (EDBE)PbCl4 embedded in the microcavity (red line). By comparison with the spectrum of Figure 1a, we noticed a sharpening of the emission centered at around 515 nm, which corresponds to the cavity mode spectral position. To prove that this effect is assigned to spectral redistribution operated by the photonic band structure, the black line of Figure 3b shows the ratio spectrum obtained, normalizing the data reported in Figure 3a by the emission of the bare (EDBE)PbCl4 thin film. There, the data display a clear enhancement (PLMC/PLREF \(>\) 1) at wavelengths corresponding to the cavity mode. To further confirm this interpretation, we collected angular resolved transmittance and photoluminescence spectra  
Figure 2: Schematic (**a,b**) and transmittance spectra (**c,d**) of a polymer half microcavity (**a,c**) and of a microcavity where the defect layer consist in an EDBE PbCl4 thin film (**b,d**). The inset of panel (**d**) is a digital photograph of the microcavity. (Figure 3c,d, respectively). Figure 3c shows that the features assigned to the PBG display the angular dispersion expected from theory [35]. In the plot, the x-axis represents the wavelength, while the y-axis represents the angle. The intensity scale is instead reported as a color code for the experimental data so that low intensities appear in red shades while high transmittance values appear in blue shades. The same plot also reports the transmittance calculated via TMM (see Methods section). In this case, only the intensity profile set at transmittance 75% is depicted as a black line in the plot. Experimental and calculated data are in full agreement. Indeed, the PBG is initially detected at 540 nm. When increasing the angle of incidence, it shifts toward the shorter wavelengths in both experimental and calculated data. The panel d of the same figure reports the photoluminescence spectra collected at different angles. We can still notice the broad (EDBE)PbCl\({}_{4}\) signal observed in Figure 1b, but in all of the spectra, we found a sharper peak with enhanced intensity moving to the shorter wavelength form 515 nm, for the spectrum collected at 10\({}^{\circ}\), to 460 nm for the one collected at 50\({}^{\circ}\). This is confirmed by the normalized spectra of Figure 3b. The dashed lines that connect panels c and d in Figure 3 guide the eye from the cavity mode detected in the transmittance spectra to the enhanced peak detected in the PL spectra. Such peaks fall on the short wavelength side of the PBG, where the cavity mode is detected, further confirming that the features observed in Figure 3a are assigned to spectral redistribution. For the data reported in Figure 3, it is possible to retrieve a quality factor (Q) for this cavity of 20-30. Q is calculated as the ratio between the spectral width and the spectral position (\(\Delta\)\(\lambda\)/\(\lambda\)) of the cavity mode. [35; 61] As suggested by its name, this finesse represents the quality of the microcavity.