Development of Perovskite (MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 Solar Cells via n-Octylammonium Iodide Surface Passivation

The influence of n-octylammonium iodide (OAI, passive layer) on the types of phases formed in a (MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 perovskite film was studied using X-ray diffraction. Using UV spectrophotometric techniques, it was determined how varied OAI additive layer ratios affected the linear and nonlinear optical characteristics of glass substrates/FTO/compact TiO2/mesoporous TiO2/(MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 films. All films’ direct optical bandgap energies were determined to be 1.54 eV. The effects of OAI addition on the films’ photoluminescence intensity and emitted colors were also investigated. For the fabricated perovskite solar cells (PSCs) without an OAI passivation layer, the corresponding power conversion efficiency (PCE), open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF) values were 18.8%, 1.02 V, 24.6 mAcm−2, and 75%, respectively. When the concentration of OAI reached 2 mg, the maximum obtained values of PCE, VOC, JSC, and FF were 20.2%, 1.06 V, 24.2 mAcm−2, and 79%, respectively. The decreased trap density and increased recombination resistance were responsible for the improvement in solar cell performance.


Introduction
Due to their ease of fabrication, organic-inorganic hybrid halide perovskites materials have emerged as effective low-cost materials for high-power-conversion-efficiency solar cells [1,2]. Hybrid halide perovskite materials exhibited improved optoelectronic properties [3], a tunable bandgap [4], a high visible light absorption coefficient [5], and a long diffusion length of photogenerated charge carriers [6]. Perovskite solar cells (PSCs) have improved their power conversion efficiency (PCE) from 3.8% [7] to 25.7% [8], but their PCE, open-circuit voltage (Voc), and fill factor (FF) are still below the theoretical values [9,10]. The performance of the devices was enhanced by improving the bulk and interface quality of the perovskite.
The nonradiative recombination rate of the charge carriers is more important than a radiative recombination mechanism in PSCs [11,12]. The nonradiative recombination occurs via shunt pathways between ETL and HTL lyres, the hole transport layer (HTL) interface, the electron transport layer (ETL) interface, and the bulk of the perovskite. In addition, the quick growth of the perovskite crystal causes defects within the structure of the perovskite materials. These defects help to create a nonradiative carrier recombination site [13]. Furthermore, there is recombination within the lattice defects created within the perovskite materials because they have energy levels inside the band gap (near the

Methods and Materials
The devices were fabricated by fluorine-doped tin-oxide (FTO)-coated glass substrates etched using the laser etching method. FTO glass substrates were cut into 2.5 cm * 1.7 cm. After that, the substrates were cleaned for 30 min by soaking and sonicating in 2% Hellmanex III in deionized water, deionized water, acetone, and ethanol, respectively. The cleaned substrates were treated with UV ozone for 30 min prior to processing. A compact TiO 2 (c-TiO 2 ) layer was deposited as the ETL layer by the spray pyrolysis method at 450 • C. More information can be obtained in [44]. A mesoporous TiO 2 (m-TiO 2 ) layer was deposited by the spin coating method as shown in [44]. The precursor solution of perovskite (MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 was prepared as shown in [45]. Different concentrations of n-octylammonium iodide (2,4, and 6 mg) were dissolved in 1 mL of isopropyl alcohol to be used as a passivation layer. The passivation layer was deposited on the perovskite layer (after cooling down) by spinning the solution (70 µL) at 6000 rpm for 30 s (acceleration rate: 2000 rpm/s 2 ). The passivated perovskite films were coated with a Spiro-MeOTAD and gold layers as shown in [45]. Figure 1 shows the device structure of the OAI-passivated PSC.

Methods and Materials
The devices were fabricated by fluorine-doped tin-oxide (FTO)-coated strates etched using the laser etching method. FTO glass substrates were cut in *1.7 cm. After that, the substrates were cleaned for 30 min by soaking and son 2% Hellmanex III in deionized water, deionized water, acetone, and ethanol, res The cleaned substrates were treated with UV ozone for 30 min prior to processin pact TiO2 (c-TiO2) layer was deposited as the ETL layer by the spray pyrolysis 450 °C. More information can be obtained in [44]. A mesoporous TiO2 (m-TiO2) deposited by the spin coating method as shown in [44]. The precursor solution skite (MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 was prepared as shown in [45]. Differe trations of n-octylammonium iodide (2,4, and 6 mg) were dissolved in 1 mL of alcohol to be used as a passivation layer. The passivation layer was deposited o ovskite layer (after cooling down) by spinning the solution (70 μL) at 6000 rp (acceleration rate: 2000 rpm/s 2 ). The passivated perovskite films were coated wi MeOTAD and gold layers as shown in [45]. Figure 1 shows the device struct OAI-passivated PSC. The film thickness was measured using the DEKTAK profilometer. The th all films was approximately the same at 500 ± 10 nm. Using X'Pert Pro (MRD) fr lytical (the goniometer has a minimum 2-step size of 0.0001°), the structure of the films was determined. The surface morphology and topography of the passivat skite layer were investigated using an atomic force microscope (AFM) (NanoSco Bruker SPMs). Fourier transform infrared (FTIR) spectra were recorded using a spectrometer (Spectrum Two FTIR, PerkinElmer). Time-resolved photolum (TRPL) was measured via time-correlated single-photon counting (TCSPC LifeSpec II (Edinburgh Instruments) fluorescence spectrometer with a picoseco diode laser (EPL-510, Edinburgh Instruments) at a 510 nm wavelength and an 8 width. A photoluminescence (PL) system with a 532 nm excitation laser source The film thickness was measured using the DEKTAK profilometer. The thickness of all films was approximately the same at 500 ± 10 nm. Using X'Pert Pro (MRD) from Panalytical (the goniometer has a minimum 2-step size of 0.0001 • ), the structure of the prepared films was determined. The surface morphology and topography of the passivated perovskite layer were investigated using an atomic force microscope (AFM) (NanoScope V from Bruker SPMs). Fourier transform infrared (FTIR) spectra were recorded using an infrared spectrometer (Spectrum Two FTIR, PerkinElmer). Time-resolved photoluminescence (TRPL) was measured via time-correlated single-photon counting (TCSPC) using a LifeSpec II (Edinburgh Instruments) fluorescence spectrometer with a picosecond pulsed diode laser (EPL-510, Edinburgh Instruments) at a 510 nm wavelength and an 85 ps pulse width. A Nanomaterials 2023, 13, 1492 4 of 18 photoluminescence (PL) system with a 532 nm excitation laser source was used to obtain the PL spectra (described in [44]). The transmittance (T) and reflectance (R) spectra of the prepared films were investigated using a double-beam spectrophotometer (Cary5000 from Varian, 200-3200 nm). Using a Cell Tester system with a Model No. CT50AAA from Photo Emission Tech, the I-V characteristics were measured with a device area of 0.158 cm 2 and an irradiation of 1000 W/m 2 . Figure 2 displays the XRD patterns of (MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 films passivated with various n-octylammonium iodide (OAI) concentrations that were deposited on glass/FTO/c-TiO 2 /m-TiO 2 . The diffraction peaks of the α-FAPbI 3 phase appeared at a 2θ of 13.76, 19.57, 24.21, 28.02, 31.34, 34.49, 40.14, and 42.63 • , which were associated with the (001), (011), (111), (002), (012), (112), (022), and (033) planes, respectively [46]. A diffraction peak of the δ-FAPbI 3 phase (unwanted) was detected at 2θ of 11.65 • [47] for the perovskite layer without OAI. Using OAI, no δ-FAPbI 3 signal should be detected in the prepared perovskite films. The (001) diffraction peak of hexagonal PbI 2 was detected at 12.6 • for the perovskite films. Furthermore, there were three additional peaks at 26.36, 33.67, and 35.82 • , which represented the FTO layer, and one peak at 37.64 • , which can be assigned to the TiO 2 phase [48]. Besides, the addition of OAI to the system did not affect the peak positions of the α-FAPbI 3 , which indicated the unchanging nature of the lattice constant of the α-FAPbI 3 phase. On the other hand, the presence of OAI influenced the peaks' intensities, which indicated a change in the crystallinity of the film. anomaterials 2023, 13, x FOR PEER REVIEW CT50AAA from Photo Emission Tech, the I-V characteristics were measured with a area of 0.158 cm 2 and an irradiation of 1000 W/m 2 . Figure 2 displays the XRD patterns of (MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 film sivated with various n-octylammonium iodide (OAI) concentrations that were de on glass/FTO/c-TiO2/m-TiO2. The diffraction peaks of the α-FAPbI3 phase appea 2θ of 13.76, 19.57, 24.21, 28.02, 31.34, 34.49, 40.14, and 42.63°, which were associat the (001), (011), (111), (002), (012), (112), (022), and (033) planes, respectively [46] fraction peak of the δ-FAPbI3 phase (unwanted) was detected at 2θ of 11.65° [47] perovskite layer without OAI. Using OAI, no δ-FAPbI3 signal should be detected prepared perovskite films. The (001) diffraction peak of hexagonal PbI2 was dete 12.6° for the perovskite films. Furthermore, there were three additional peaks a 33.67, and 35.82°, which represented the FTO layer, and one peak at 37.64°, which assigned to the TiO2 phase [48]. Besides, the addition of OAI to the system did no the peak positions of the α-FAPbI3, which indicated the unchanging nature of th constant of the α-FAPbI3 phase. On the other hand, the presence of OAI influen peaks' intensities, which indicated a change in the crystallinity of the film.   Each passivant (2, 4, and 6 mg/mL in isopropanol) was coated on top of per (MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 in order to investigate the potential interacti tween the passivants and perovskite. Fourier transform infrared (FTIR) spectrosco used to study changes in the chemical bonds ( Figure 3). Five distinct changes c observed in the IR spectra following the OAI treatment. (i) A broad peak centered 3760 cm −1 was produced in all the OAI-treated samples, signaling the structural groups' stretching vibrations [49]. (ii) A strong band appeared around 2400 cm −1 Each passivant (2, 4, and 6 mg/mL in isopropanol) was coated on top of perovskite (MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 in order to investigate the potential interactions between the passivants and perovskite. Fourier transform infrared (FTIR) spectroscopy was used to study changes in the chemical bonds ( Figure 3). Five distinct changes could be observed in the IR spectra following the OAI treatment. (i) A broad peak centered around 3760 cm −1 was produced in all the OAI-treated samples, signaling the structural H-O-H groups' stretching vibrations [49]. (ii) A strong band appeared around 2400 cm −1 , which can be assigned to the structural N−H groups. (iii) The N-H rocking bands ranged between 1100 and 1300 cm −1 [50]. (iv) In addition, the NH 3 asymmetric bending mode, which indicates FA + , occurred in the 1460-1472 cm −1 region [51,52]. (v) The C-N rocking bands, which revealed the perovskite layer, were apparent in the 960-1000 cm −1 range [52]. The OAI-treated perovskite film peaks' blue and red shifts were evidence of the strong symmetrical interactions between the perovskite films and the functional groups of OAI. According to the FTIR data, OAI can passivate the defects of the interfaces and grain boundaries of perovskite films.

Results and Discussion
Nanomaterials 2023, 13, x FOR PEER REVIEW interactions between the perovskite films and the functional groups of OAI. Acco the FTIR data, OAI can passivate the defects of the interfaces and grain boun perovskite films.     (RMS) of about 42.6 and 53.5 nm, respectively. After OAI passivation, there were significant changes in the grain size, grain boundaries, and surface roughness. This showed that the post-treatment passivation had an impact on the perovskite morphology. The surface roughness increased as the OAI concentration increased, as shown in Table 1. Compared to pristine perovskite films, the perovskite films with OAI were smoother with a smaller surface roughness between 32.8 and 36.6 nm. As shown in Table 1, the surface roughness increased with the increase in the concentration of OAI. Nonradiative recombination decreased as the surface roughness decreased. Furthermore, the small surface roughness was favorable for HTM layer deposition and reduced the interface resistance to speed up the charge transfer [53].   To investigate the change in the charge carrier dynamics, we employed time-resolved photoluminescence (TRPL). We measured the TRPL spectra for both the 0OAI and 2OAI films deposited on the glass substrate ( Figure 5). The decay time was obtained for both films by fitting the TRPL curves with a mono-exponential function. We observed a significant improvement where the lifetime was more than 60% longer for the 2 OAI in comparison to the 0 OAI films, as shown in Table 2. This indicated a suppression of nonradiative recombination at the surface of the perovskite layer, leading to better interfacial contact between the perovskite and the HTL.  To investigate the change in the charge carrier dynamics, we employed time-resolved photoluminescence (TRPL). We measured the TRPL spectra for both the 0OAI and 2OAI films deposited on the glass substrate ( Figure 5). The decay time was obtained for both films by fitting the TRPL curves with a mono-exponential function. We observed a significant improvement where the lifetime was more than 60% longer for the 2 OAI in comparison to the 0 OAI films, as shown in Table 2. This indicated a suppression of nonradiative recombination at the surface of the perovskite layer, leading to better interfacial contact between the perovskite and the HTL.  The optical performance of hybrid perovskite films is essential for efficient p taic devices. Figure 6 shows the spectrum distribution of transmission T(λ) and R(λ) of glass/FTO/c-TiO2/m-TiO2/(MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 films with concentrations of OAI. In general, the value of T(λ) was less than 2% in the region 190 and 600 nm; however, it gradually increased with increasing λ in the vis infrared region (600-1200 nm). In the region above λ = 800 nm, all films almos transparent (i.e., Reflectance + Transmittance = 1) due to the limited energy loss a of scattering. The inequality (Reflectance + Transmittance < 1) at shorter wavelen 600 nm) was caused by the presence of absorption. The enhancement of optical geneous thin films was indicated by longer-wavelength interference spectra [5 the transmittance spectra, films with 4 and 6 OAI had the maximum transmitta thermore, the reflectance gradually increased as the wavelength ranged from 19 nm. The interference phenomenon led to some reflectance oscillations at differe lengths [55]. The reflectance oscillations proved the films' optical homogeneity [  The optical performance of hybrid perovskite films is essential for efficient photovoltaic devices. Figure 6 shows the spectrum distribution of transmission T(λ) and reflection R(λ) of glass/FTO/c-TiO 2 /m-TiO 2 /(MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 films with different concentrations of OAI. In general, the value of T(λ) was less than 2% in the region between 190 and 600 nm; however, it gradually increased with increasing λ in the visible-near infrared region (600-1200 nm). In the region above λ = 800 nm, all films almost became transparent (i.e., Reflectance + Transmittance = 1) due to the limited energy loss as a result of scattering. The inequality (Reflectance + Transmittance < 1) at shorter wavelengths (λ < 600 nm) was caused by the presence of absorption. The enhancement of optically homogeneous thin films was indicated by longer-wavelength interference spectra [54]. From the transmittance spectra, films with 4 and 6 OAI had the maximum transmittance. Furthermore, the reflectance gradually increased as the wavelength ranged from 190 to 1200 nm. The interference phenomenon led to some reflectance oscillations at different wavelengths [55]. The reflectance oscillations proved the films' optical homogeneity [55]. The electronic transition in semiconductor materials can be illustrated using band theory [56]. An electron in molecules move from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) when electromagnetic radiation is absorbed [56,57]. Therefore, for a molecular crystal, the HOMO orbital (π-orbital) shares the valence band (VB), while the conduction band (CB) is formed by the combination of the LUMO orbitals (π⃰ -orbitals). The band gap is between VB and CB. The band gap (Eg) can be computed from the spectral position of the optical absorption edge. The best fitting of the experimental data to Tauc's equation (αhυ = B(hυ − Eg) ɣ ) was obtained when γ = 0.5, so the direct allowed transition was the type of electronic transition [58,59], which is represented in Figure 7 for glass/FTO/c-TiO2/m-TiO2/(MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 films with a different concentration of OAI. The values of Eg for all films were found to be 1.54 eV, which were not impacted by the OAI amount. The unchanging band gap is compatible with the lattice parameters remaining unchanged, as discussed in the XRD part. When alkaline earth metal chloride, BCl2 (B = Mg, Ca, Sr, and Ba), was added to the FAPbI3 perovskite, a similar result was found [60]. The electronic transition in semiconductor materials can be illustrated using band theory [56]. An electron in molecules move from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) when electromagnetic radiation is absorbed [56,57]. Therefore, for a molecular crystal, the HOMO orbital (π-orbital) shares the valence band (VB), while the conduction band (CB) is formed by the combination of the LUMO orbitals (π * -orbitals). The band gap is between VB and CB. The band gap (E g ) can be computed from the spectral position of the optical absorption edge. The best fitting of the experimental data to Tauc's equation (αhυ = B(hυ − E g ) G ) was obtained when γ = 0.5, so the direct allowed transition was the type of electronic transition [58,59], which is represented in Figure 7 for glass/FTO/c-TiO 2 /m-TiO 2 /(MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 films with a different concentration of OAI. The values of E g for all films were found to be 1.54 eV, which were not impacted by the OAI amount. The unchanging band gap is compatible with the lattice parameters remaining unchanged, as discussed in the XRD part. When alkaline earth metal chloride, BCl 2 (B = Mg, Ca, Sr, and Ba), was added to the FAPbI 3 perovskite, a similar result was found [60].
The photoluminescence (PL) emissions of glass/FTO/c-TiO 2 /m-TiO 2 / (MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 films with and without OAI were also examined. As revealed in Figure 8a, the perovskite steady-state PL graphs showed a typical and high luminescence peak at sites that matched the absorption edges seen in UV-Vis measurements (Figure 8c). All layers of perovskite samples (FTO, c-TiO 2 , m-TiO 2 , and perovskite) were the same for all samples, so the change in PL intensity was affected by the OAI-passivated layer. In contrast to the film without OAI, the films of (MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 with 2OAI and 6OAI had higher PL intensities (Figure 8b), indicating that the OAI additive can greatly reduce trap-mediated and nonradiative recombination in the perovskite layer [61]. The OAI additive affected the crystallinity of those perovskite films (XRD part). The amount of defects created in the entire (MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 film decreased or increased as the crystallinity of the films increased or decreased, and this affected the recombination traps in the perovskite films. Accordingly, the optoelectronic features of perovskite films were improved because the nonradiative recombination pathway was restrained. Conversely, the PL intensity of the (MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 film with 4OAI was reduced because of the increase in the density of microstructural defects [61]. so the direct allowed transition was the type of electronic transition [58,59], which is represented in Figure 7 for glass/FTO/c-TiO2/m-TiO2/(MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 films with a different concentration of OAI. The values of Eg for all films were found to be 1.54 eV, which were not impacted by the OAI amount. The unchanging band gap is compatible with the lattice parameters remaining unchanged, as discussed in the XRD part. When alkaline earth metal chloride, BCl2 (B = Mg, Ca, Sr, and Ba), was added to the FAPbI3 perovskite, a similar result was found [60]. The photoluminescence (PL) emissions of glass/FTO/c-TiO2/m-TiO2/(MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 films with and without OAI were also examined. As revealed in Figure 8a, the perovskite steady-state PL graphs showed a typical and high luminescence peak at sites that matched the absorption edges seen in UV-Vis measurements ( Figure 8c). All layers of perovskite samples (FTO, c-TiO2, m-TiO2, and perovskite) were the same for all samples, so the change in PL intensity was affected by the OAIpassivated layer. In contrast to the film without OAI, the films of (MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 with 2OAI and 6OAI had higher PL intensities ( Figure  8b), indicating that the OAI additive can greatly reduce trap-mediated and nonradiative recombination in the perovskite layer [61]. The OAI additive affected the crystallinity of those perovskite films (XRD part). The amount of defects created in the entire (MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 film decreased or increased as the crystallinity of the films increased or decreased, and this affected the recombination traps in the perovskite films. Accordingly, the optoelectronic features of perovskite films were improved because the nonradiative recombination pathway was restrained. Conversely, the PL intensity of the (MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 film with 4OAI was reduced because of the increase in the density of microstructural defects [61].
The real component of the complex refractive index is defined as the reflective index (n), which is related to the speed of electromagnetic wave propagation throughout thin films and gives the details of electronic polarization. However, the imaginary component is known as the extinction coefficient (k), which is linked to the decay of the magnitude of the incident electric field's oscillations. The following relations were used to determine the values of n and k for all films [58,59]: (1) The real component of the complex refractive index is defined as the reflective index (n), which is related to the speed of electromagnetic wave propagation throughout thin films and gives the details of electronic polarization. However, the imaginary component is known as the extinction coefficient (k), which is linked to the decay of the magnitude of the incident electric field's oscillations. The following relations were used to determine the values of n and k for all films [58,59]: where α is the absorption coefficient = 2.303 * bsorbance/thickness of the film. The n (λ) and k (λ) values for glass/FTO/c-TiO 2 /m-TiO 2 /(MACl) 0.33 FA 0.99 MA 0.01 Pb (I 0.99 Br 0.01 ) 3 films with OAI concentrations are presented in Figure 9. The maximum n (λ) value was between =1000 and 1100 nm (Figure 9a). Figure 9b shows a maximum value for k (λ) curves with wavelength values between =300 and 650 nm. The spectrum can be divided into two regions based on the wavelength to study the dispersion of the reflective index. The first region at λ < 520 nm (see Figure 9a), in which the n values showed an anomalous dispersion, while in the second region λ >520 nm, the n values had many peaks (n exhibited both normal and anomalous dispersion) [62]. The change in the film's absorption, density, and polarizability may be the reason for the variation in the n and k values because of the addition of the OAI layers [57].  Figure 9. The maximum n (λ) value was between =1000 and 1100 nm (Figure 9a). Figure  9b shows a maximum value for k (λ) curves with wavelength values between =300 and 650 nm. The spectrum can be divided into two regions based on the wavelength to study the dispersion of the reflective index. The first region at λ < 520 nm (see Figure 9a), in which the n values showed an anomalous dispersion, while in the second region λ ˃ 520 nm, the n values had many peaks (n exhibited both normal and anomalous dispersion) [62]. The change in the film's absorption, density, and polarizability may be the reason for the variation in the n and k values because of the addition of the OAI layers [57]. Understanding the optical characteristics of semiconductors requires computing the complex dielectric constant (ε = ε r + iε i ). The real component of the dielectric constant (ε r ) provides information about the material's optical dispersion, whereas the imaginary component of the dielectric constant (ε i ) gives information about the wave's dissipative rate in the material. The energy loss produced by fast electrons as they pass through the surface and bulk of a material are described by the surface and volume energy loss functions (SELF, VELF), respectively. The following relations can be used to define the values of ε r , ε i , SELF, and VELF [58,59]:   As revealed in Figure 10a,b, the values of εr were higher than the values of εi. Furthermore, as the wavelength increased, the values of εr increased slightly. Furthermore, the values of εi increased with the wavelength up to 400-500 nm, then decreased with the wavelength, remaining stable beyond 800 nm. The addition of OAI affected the dielectric constants, where at the lower wavelength range, εr enhanced, while εi reduced as the system contained OAI. The charge displacement and the polarization in crystal affected the dielectric constants. The changes in the values of εr and εi at low wavelengths were assigned to the strong absorption bands. Figure 10c,d show both SELF and VELF as functions of wavelength. It was evident that the free charge carriers lost about the same amount of energy when passing through the surface and bulk material. The values of SELF were less than the values of VELF for the incident photons due to the charge carriers traveling a long distance through the bulk material, resulting in more collisions with the charges within the material [63]. The SELF and VELF values of all films in the wavelength ranging up to 600 nm changed dramatically depending on the amount of OAI. After that, the SELF and VELF values of all films were almost unchanged. As revealed in Figure 10a,b, the values of ε r were higher than the values of ε i . Furthermore, as the wavelength increased, the values of ε r increased slightly. Furthermore, the values of ε i increased with the wavelength up to 400-500 nm, then decreased with the wavelength, remaining stable beyond 800 nm. The addition of OAI affected the dielectric constants, where at the lower wavelength range, ε r enhanced, while ε i reduced as the system contained OAI. The charge displacement and the polarization in crystal affected the dielectric constants. The changes in the values of ε r and ε i at low wavelengths were assigned to the strong absorption bands. Figure 10c,d show both SELF and VELF as functions of wavelength. It was evident that the free charge carriers lost about the same amount of energy when passing through the surface and bulk material. The values of SELF were less than the values of VELF for the incident photons due to the charge carriers traveling a long distance through the bulk material, resulting in more collisions with the charges within the material [63]. The SELF and VELF values of all films in the wavelength ranging up to 600 nm changed dramatically depending on the amount of OAI. After that, the SELF and VELF values of all films were almost unchanged.
The optical conductivity (σ opt ) is an optical characteristic that provides details about the material's electronic state. Furthermore, it represents the electrical conductivity of the material, which is based on free charge carriers that are produced via the electric field linked to the incident light. The following formula can be used to determine σ opt [58,59]: where n, α, and c are the refractive index, absorption coefficient of the material, and the velocity of light, respectively. The variation in the wavelength for glass/FTO/c-TiO 2 /m-TiO 2 /(MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 films with different concentrations of OAI are displayed in Figure 11a. As depicted in Figure 11a, the values of σ opt demonstrated a linear behavior that was symmetric with respect to both α and n based on Equation (7) (Figure 11b). The graph shows the highest value in the wavelength range between λ = 300 and 500 nm, due to the strong absorption through thin films in this region [64]. Beyond this range, σ opt reduced with increasing wavelength. The optical conductivity (σopt) is an optical characteristic that provides details about the material's electronic state. Furthermore, it represents the electrical conductivity of the material, which is based on free charge carriers that are produced via the electric field linked to the incident light. The following formula can be used to determine σopt [58,59]: where n, α, and c are the refractive index, absorption coefficient of the material, and the velocity of light, respectively. The variation in the wavelength for glass/FTO/c-TiO2/m-TiO2/(MACl)0.33FA0.99MA0.01Pb(I0.99Br0.01)3 films with different concentrations of OAI are displayed in Figure 11a. As depicted in Figure 11a, the values of σopt demonstrated a linear behavior that was symmetric with respect to both α and n based on Equation (7) ( Figure  11b). The graph shows the highest value in the wavelength range between λ = 300 and 500 nm, due to the strong absorption through thin films in this region [64]. Beyond this range, σopt reduced with increasing wavelength. The interaction between the electromagnetic field of the incident light and an inherent charge in the material caused a change in its phase, frequency, amplitude, or polarization. The study of these interactions is known as nonlinear optics (NLO). The NLO parameters of materials have significance in their application in many application fields, such as medicine, telecommunications technology, data and imaging, and sensors [65]. According to Miller's formula, which is dependent on the linear optical susceptibility (χ (1) ), the third-order non-linear optical susceptibility (χ (3) ) and the non-linear refractive index (n2) can be obtained [58,59]: 1.7 * 10 * 1.7 * 10 * 1 4 (9) 12 *  The interaction between the electromagnetic field of the incident light and an inherent charge in the material caused a change in its phase, frequency, amplitude, or polarization. The study of these interactions is known as nonlinear optics (NLO). The NLO parameters of materials have significance in their application in many application fields, such as medicine, telecommunications technology, data and imaging, and sensors [65]. According to Miller's formula, which is dependent on the linear optical susceptibility (χ (1) ), the thirdorder non-linear optical susceptibility (χ (3) ) and the non-linear refractive index (n 2 ) can be obtained [58,59]: χ (3) = 1.7 * 10 −10 * (χ (1) ) 4 = 1.7 * 10 −10 * ( n 2 − 1 4π ) 4 (9) The modifications of the χ (1) , χ (3) , and n 2 values for glass/FTO/c-TiO 2 /m-TiO 2 / (MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 films with OAI concentrations against the wavelength are shown in Figure 12a-c. The NLO parameters changed in similarity, as seen in Figure 12a-c, where the χ (1) , χ (3) , and n 2 curves display three peaks around 570, 860, and 1020 nm. The NLO parameters reached their greatest values in the IR region. The NLO parameters for films contained 4 and 6 OAI, which were enhanced at 570 nm, as compared with the other films.  Table 3 lists the obtained parameters. As revealed from Figure 13a-e and Table 3, the changing concentration of OAI affected the overall PSC devices' performance. The fabricated PSCs without OAI passivation had a power conversion efficiency (PCE), open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF) of 18.8%, 1.02 V, 24.6 mAcm −2 , and 75%, respectively. The efficiency of the fabricated PSCs was impacted by the OAI passivation layer. The VOC, FF, and PCE first increased as the amount of OAI became 2 mg, then reduced with more additives of OAI. The value of JSC decreased as the amount of OAI increased. The maximum PCE value of 20.2% was obtained for the passivation layer of a 2 mg OAI concertation. The increase in the PCE can be attributed to the improved VOC (1.06 V) and FF (79%) and the reduction in the JSC (24.2 mAcm −2 ) value after OAI treatment. For the OAI-passivated PSCs, the VOC increased due to a decrease in nonradiative recombination [15,66], while the reduction in JSC indicated the enhancement of charge collection [15]. As shown in Figure 13d, the FF decreased slightly as the amount of OAI additives increased. Furthermore, additional passivation solutions, such as PMMA:PCBM, increased the voltage while decreasing the FF [67,68]. In summary, the The PSCs were fabricated using (MACl) 0.33 FA 0.99 MA 0.01 Pb(I 0.99 Br 0.01 ) 3 perovskite films with OAI concentrations to study the impact of OAI on the photovoltaic parameters. Figure 13a displays the photocurrent density-voltage (J-V) curves for the PSCs, and Table 3 lists the obtained parameters. As revealed from Figure 13a-e and Table 3, the changing concentration of OAI affected the overall PSC devices' performance. The fabricated PSCs without OAI passivation had a power conversion efficiency (PCE), open-circuit voltage (V OC ), short-circuit current density (J SC ), and fill factor (FF) of 18.8%, 1.02 V, 24.6 mAcm −2 , and 75%, respectively. The efficiency of the fabricated PSCs was impacted by the OAI passivation layer. The V OC , FF, and PCE first increased as the amount of OAI became 2 mg, then reduced with more additives of OAI. The value of J SC decreased as the amount of OAI increased. The maximum PCE value of 20.2% was obtained for the passivation layer of a 2 mg OAI concertation. The increase in the PCE can be attributed to the improved V OC (1.06 V) and FF (79%) and the reduction in the J SC (24.2 mAcm −2 ) value after OAI treatment. For the OAI-passivated PSCs, the V OC increased due to a decrease in nonradiative recombination [15,66], while the reduction in J SC indicated the enhancement of charge collection [15]. As shown in Figure 13d, the FF decreased slightly as the amount of OAI additives increased. Furthermore, additional passivation solutions, such as PMMA:PCBM, increased the voltage while decreasing the FF [67,68]. In summary, the OAI-passivated layer enhanced the performance parameters of the PSCs due to the decrease in the recombination trap states and improved charge collection [15]. OAI-passivated layer enhanced the performance parameters of the PSCs due to the decrease in the recombination trap states and improved charge collection [15].

Conclusions
The perovskite's crystal structure was unaffected by the addition of OAI. The addition of OAI did not change the band gap of the films. A typical and high peak luminescence can be seen on all films' steady-state PL graphs. The PL emission intensity of the film prepared with 6 mg OAI indicated nonradiative carrier recombination. The refractive index values showed both anomalous and/or normal dispersion depending on the wavelength range. As a result of the changes in the optical conductivity and the dielectric constant values caused by the addition of the OAI passivation layer, they may be suitable for use in a variety of solar cell applications. The use of the passivated films in many nonlinear devices is recommended because of the changes in the values of the NLO parameters. As the amount of OAI additive increased, the J SC slightly decreased for all devices, whereas the PCE, V OC , and FF were enhanced. The maximum PCE was obtained when the passivation layer amount reached 2 mg of OAI. The decrease in the recombination trap states and the improved charge collection of the OAI-passivated cell were the reasons for the enhanced photovoltaic parameters.  Data Availability Statement: Data will be made available upon request.