## 3 Results and Discussion  
Figure 2a,b plot the XRD pattern of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl perovskite on the glass substrate and AlN/sapphire substrate, respectively. Figure 2c shows the XRD pattern of Figure 2b with 7 times magnification. Six XRD spectra peaks of perovskite-like (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl on the AlN/sapphire substrate and glass substrate were observed at around 10.83\({}^{\circ}\), 16.15\({}^{\circ}\), 21.50\({}^{\circ}\), 26.90\({}^{\circ}\), 32.38\({}^{\circ}\), and 37.93\({}^{\circ}\), corresponding to the (004), (006), (008), (0010), (0012), and (0014)  
Figure 1: Structure of the perovskite-like (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl on the AlN/sapphire substrate heterostructure. phases of the quasi-2D (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl structure, respectively [16; 17]. The domain sizes D of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl perovskite on the glass substrate and AlN/sapphire substrate were 50.7 and 17.1 nm, respectively, and were calculated using the Scherrer equation [18]. The crystallite size D of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl film was  
\[\text{D}=\frac{k\lambda}{\beta cos\theta} \tag{1}\]  
where \(k\) is the Scherrer constant, \(\lambda\) is the wavelength of the radiation (1.54 A for the Cu target), and \(\beta\) and \(\theta\) are the FWHM and Bragg angle of the (0010) phase, respectively. The degradation in crystal quality may have contributed to the preferred orientation of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl perovskite, which was destroyed by the lattice of the AlN/sapphire substrate due to strained force. Figure 2: XRD pattern of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl perovskite on (**a**) glass and (**b**) AlN/sapphire. (**c**) XRD pattern of (**b**) with 7 times magnification. Figure 3a,b show the top-view SEM image of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl perovskite on AlN/sapphire without and with 300 \({}^{\circ}\)C annealing, respectively. The typical structure of (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl perovskite is hexagonal [19]. For the pristine sample, oval- or round-shaped particles were observed on the surface of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl perovskite film on the AlN/sapphire substrate. This may have been caused by the lattice mismatch during (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl perovskite crystal growth (aggregation), thereby causing changes in the crystal shape. However, after annealing at 300 \({}^{\circ}\)C for 10 min, the structure of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl perovskite crystal was destroyed, as shown in Figure 3b. Figure 4a shows the photoluminescence (PL) spectra of the perovskite-like material (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl on the glass substrate and AlN/sapphire substrate heterostructure, respectively. Figure 4b shows the normalized PL spectra of Figure 4a. The peak positions of PL spectra were 400 and 372 nm, with a full width at half maximum (FWHM) of 15 and 85 nm, respectively. It is well known that perovskite materials have excellent preferred-orientation crystallinity and defect allowance [20; 21]. The PL spectrum of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl showed a very narrow FWHM on the glass substrate and a broad FWHM on the AlN/sapphire substrate heterostructure, with the latter indicating degradation of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl film crystal quality. A blue shift in the peak position of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl film from 400 to 4000 nm, is shown in Figure 4c. The peak positions of PL spectra were 400 and 372 nm, with a full width at half maximum (FWHM) of 15 and 85 nm, respectively. It is well known that perovskite materials have excellent preferred-orientation crystallinity and defect allowance [20; 21]. The PL spectrum of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl showed a very narrow FWHM on the glass substrate and a broad FWHM on the AlN/sapphire substrate heterostructure, with the latter indicating degradation of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl film crystal quality. A blue shift in the peak position of the (PEA)\({}_{2}\)PbBr\({}_{3}\)Cl film from 400 to 4000 nm, is shown in Figure 4d.